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WEATHER AND CLIMATE

WEATHER AND CLIMATE

© 2008 Editorial Sol 90All rights reserved.

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Weather and Climate

Contents PHOTOGRAPH ON PAGE 1Tornado during an electricalstorm, in Oklahoma, 1973

Climatology

Page 18

Surface Factors

Page 62

Meteorology

Page 74

Climate Change

Page 36

MeteorologicalPhenomena

The flutter of a butterfly's wings inBrazil can unleash a tornado inFlorida.” That was the conclusion

arrived at in 1972 by Edward Lorenz afterdedicating himself to the study ofmeteorology and trying to find a way ofpredicting meteorological phenomena that

might put the lives of people atrisk. In effect, the atmosphereis a system so complicatedthat many scientists defineit as chaotic. Any forecastcan rapidly deterioratebecause of the wind, theappearance of a warmfront, or an unexpectedstorm. Thus, thedifference continuesto growgeometrically, andthe reality of thenext day is not theone that wasexpected butentirely

different: when there should have been sunshine,there is rain; people who planned to go to thebeach find they have to shut themselves up in thebasement until the hurricane passes. All thisuncertainty causes many people who live in areasthat are besieged by hurricanes or tropicalstorms to live in fear of what might happen,because they feel very vulnerable to changes inweather. It is also true that natural phenomena,such as tornadoes, hurricanes, and cyclones, donot in themselves cause catastrophes. Forexample, a hurricane becomes a disaster andcauses considerable damage, deaths, andeconomic losses only because it strikes apopulated area or travels over farmland. Yet insociety, the idea persists that natural phenomenaequate to death and destruction. In fact,experience shows that we have to learn to livewith these phenomena and plan ahead for whatmight happen when they occur. In this book,along with spectacular images, you will finduseful information about the factors thatdetermine weather and climate, and you will beable to understand why long-term forecasts areso complicated. What changes are expected ifglobal warming continues to increase? Could thepolar ice caps melt and raise sea levels? Couldagricultural regions slowly become deserts? Allthis and much more are found in the pages of thebook. We intend to arouse your curiosity aboutweather and climate, forces that affect everyone.

A Sum of FactorsSTRONG WINDS ANDTORRENTIAL RAINS Between September 20 andSeptember 25, 1998,Hurricane Georges lashed theCaribbean, leaving thousandsof people homeless.

“

Climatology GLOBAL EQUILIBRIUM 8-9

PURE AIR 10-11

ATMOSPHERIC DYNAMICS 12-13

COLLISION 14-15

COLORS IN THE SKY 16-17

SATELLITE IMAGEIn this image of the Earth,one clearly sees the movementof water and air, which causes,among other things,temperature variations.

The constantly movingatmosphere, the oceans, thecontinents, and the greatmasses of ice are the principalcomponents of the

environment. All these constitute what iscalled the climatic system; theypermanently interact with one anotherand transport water (as liquid or vapor),electromagnetic radiation, and heat.

Within this complex system, one of thefundamental variables is temperature,which experiences the most change andis the most noticeable. The wind isimportant because it carries heat and

moisture into the atmosphere. Water,with all its processes (evaporation,condensation, convection), also plays afundamental role in Earth's climaticsystem.

8 CLIMATOLOGY WEATHER AND CLIMATE 9

Global EquilibriumT

he Sun's radiation delivers a large amount of energy,which propels the Earth's extraordinary mechanism calledthe climatic system. The components of this complex

system are the atmosphere, hydrosphere, lithosphere,cryosphere, and biosphere. All these components are constantlyinteracting with one another via an interchange of materials andenergy. Weather and climatic phenomena of the past—as wellas of the present and the future—are the combined expressionof Earth's climatic system.

EVAPORATIONThe surfaces of waterbodies maintain thequantity of water vaporin the atmospherewithin normal limits.

PRECIPITATIONWater condensing in theatmosphere forms droplets, andgravitational action causes themto fall on different parts of theEarth's surface.

SOLAR RADIATIONAbout 50 percent of the solarenergy reaches the surface of theEarth, and some of this energy istransferred directly to differentlayers of the atmosphere. Much ofthe available solar radiation leavesthe air and circulates within theother subsystems. Some of thisenergy escapes to outer space.

BiosphereLiving beings (such as plants)influence weather and climate. Theyform the foundations of ecosystems,which use minerals, water, and otherchemical compounds. They contributematerials to other subsystems.

LithosphereThis is the uppermost solid layer ofthe Earth's surface. Its continualformation and destruction change thesurface of the Earth and can have alarge impact on weather and climate.For example, a mountain range can

act as a geographic barrierto wind and moisture.

CryosphereRepresents regions of the Earthcovered by ice. Permafrost existswhere the temperature of the soilor rocks is below zero. Theseregions reflect almost all the lightthey receive and play a role in thecirculation of the ocean, regulatingits temperature and salinity.

AtmospherePart of the energy receivedfrom the Sun is captured by theatmosphere. The other part isabsorbed by the Earth orreflected in the form of heat.Greenhouse gases heat up theatmosphere by slowing therelease of heat to space.

HUMANACTIVITY

80% ALBEDO OF RECENTLYFALLEN SNOW

The percentage of solarradiation reflected by theclimatic subsystems.

ALBEDO

about 10%ALBEDO OF THE TROPICAL FORESTS

3%ALBEDO OF THEBODIES OF WATER

ASHESVolcanic eruptions bring nutrients tothe climatic system where the ashesfertilize the soil. Eruptions also blockthe rays of the Sun and thus reduce theamount of solar radiation received bythe Earth's surface. This causes coolingof the atmosphere.

SMOKEParticles that escapeinto the atmospherecan retain their heatand act ascondensation nucleifor precipitation.

WINDSThe atmosphere is always inmotion. Heat displaces massesof air, and this leads to thegeneral circulation of theatmosphere.

SUN

UNDERGROUND CIRCULATIONThe circulation of water isproduced by gravity. Water fromthe hydrosphere infiltrates thelithosphere and circulates thereinuntil it reaches the large waterreservoirs of lakes, rivers,and oceans.

RETURN TO THE SEA

MARINE CURRENTS

Night and day, coastalbreezes exchange energybetween the hydrosphereand the lithosphere.

HEAT

HEAT

SunEssential for climatic activity.The subsystems absorb,exchange, and reflect energythat reaches the Earth's surface.For example, the biosphereincorporates solar energy viaphotosynthesis and intensifiesthe activity of the hydrosphere.

HydrosphereThe hydrosphere is the name for allwater in liquid form that is part of theclimatic system. Most of the lithosphereis covered by liquid water, and some ofthe water even circulates through it.

50%THE ALBEDO OFLIGHT CLOUDS

Some gases in the atmosphere are veryeffective at retaining heat. The layer ofair near the Earth's surface acts as ashield that establishes a range oftemperatures on it, within which lifecan exist.

GREENHOUSE EFFECT

SOLARENERGY

OZONELAYER

AT

MO

SP

HER

E

Pure Air


The atmosphere is the mass of air thatenvelops the surface of the Earth. Itscomposition allows it to regulate the quantity

and type of solar energy that reaches the surface ofthe Earth. The atmosphere, in turn, absorbs energyradiated by the crust of the Earth, the polar icecaps and the oceans, and other surfaces on theplanet. Although nitrogen is its principalcomponent, it also contains other gases, such asoxygen, carbon dioxide, ozone, and water vapor.These less abundant gases, along withmicroscopic particles in the air, have a greatinfluence on the Earth's weather and climate.

AVERAGE TEMPERATUREOF THE EARTH'S SURFACE

59° F(15° C)

Nitrogen78%

Oxygen21%

Argon0.93%

Other gases0.03%

Carbondioxide0.04%

GASES IN THE AIR

51%of solarradiation isabsorbed by theEarth's surface.

4%A small amount ofsolar radiation isreflected by the oceansand the ground.

Safe flightsThe absence ofmeteorologicalchanges in this regionmakes it safer forcommercial flights.

High mountainsAny mountains higher than 5miles (8 km) above sea level.The decrease of oxygen withaltitude makes it difficult tobreathe above 2.5 miles (4 km).

TROPOSPHERE Starts at sea level and goes to analtitude of six miles (10 km). It providesconditions suitable for life to exist. Itcontains 75 percent of the gases in theatmosphere. Meteorological conditions,such as the formation of clouds andprecipitation, depend on its dynamics. Itis also the layer that contains pollutiongenerated by human activities.

STRATOSPHERE Extends from an altitude of 6miles to 30 miles (10-50 km).The band from 12 to 19 miles(20-30 km) has a highconcentration of ozone, whichabsorbs ultraviolet radiation. Athermal inversion is producedin this layer that is expressedas an abrupt temperatureincrease beginning at analtitude of 12 miles (20 km).

MESOSPHERE Located between an altitudeof 30 to 55 miles (50-90km), it absorbs very littleenergy yet emits a largeamount of it. This absorptiondeficit causes thetemperatures to decreasefrom 60° F to -130° F (20° Cto -90° C) in the upperboundary of the mesopause.

THERMOSPHERE Found between an altitudeof 55 and 300 miles (90-500 km). The O2 and the N2absorb ultraviolet rays andreach temperatures greaterthan 1,800° F (1,000° C).These temperatures keepthe density of gases in thislayer very low.

EXOSPHERE This layer, which begins at analtitude of about 310 miles(500 km), is the upper limit ofthe atmosphere. Here materialin plasma form escapes fromthe Earth, because the magneticforces acting on them aregreater than those of gravity.

Tropical stormclouds

Cirrus

20%of solar radiationis reflected bythe clouds.

Noctilucent cloudsThe only clouds thatexist above thetroposphere. They arethe objects of intensestudy.

ForecastsWeather balloons areused to make weatherforecasts. They recordthe conditions of thestratosphere.

Cosmic raysCome from the Sun andother radiation sources inouter space. When theycollide with the moleculesof gas in the atmosphere,they produce a rain ofparticles.

Rocket probesUsed for scientificstudies of thehigher regions ofthe atmosphere

AurorasCreated in the upper layersof the atmosphere when thesolar wind generateselectrically charged particles

Meteorsbecome superheated byfriction with themolecules of the gas inthe atmosphere.Particles that skipacross the atmosphereare called shooting stars.

19%of solar radiationis absorbed bythe gases in theatmosphere.

6%of solar radiationis reflected bythe atmosphere.

Military satellitesAir friction shortenstheir useful life.

DISTANT ORBITSPolar meteorologicalsatellites orbit in theexosphere.

SO

LAR

RA

DIA

TIO

N

GREENHOUSEEFFECTProduced by theabsorption ofinfrared emissionsby the greenhousegases in theatmosphere. Thisnaturalphenomenon helpsto keep the Earth'ssurfacetemperature stable.

The Ozone Layerstops most of theSun's ultraviolet rays.


Masses of coldair descend andprevent cloudsfrom forming.

CORIOLIS FORCEThe Coriolis effect is an apparent deflectionof the path of an object that moves within arotating coordinate system. The Corioliseffect appears to deflect the trajectory ofthe winds that move over the surface of theEarth, because the Earth moves beneath thewinds. This apparent deflection is to theright in the Northern Hemisphere and to theleft in the Southern Hemisphere. The effectis only noticeable on a large scale because ofthe rotational velocity of the Earth.

IntertropicalConvergenceZone (ITCZ)

TRADE WINDSThese winds blowtoward the Equator.

The descending airforms an area of highpressure (anticyclone).

The wind blowsfrom a high- towarda low-pressure area.

Warm air rises andforms an area of lowpressure (cyclone).

3

1

6

5

24A

B

The rising airleads to theformation ofclouds.

Changes in CirculationIrregularities in the topography of thesurface, abrupt changes in temperature,

and the influence of ocean currents can alterthe general circulation of the atmosphere.These circumstances can generate waves in theair currents that are, in general, linked to thecyclonic zones. It is in these zones that stormsoriginate, and they are therefore studied withgreat interest. However, the anticyclone andthe cyclone systems must be studied togetherbecause cyclones are fed by currents of aircoming from anticyclones.

Forces in the upper-air currents, along withsurface conditions, may cause air currents toflow together or may split them apart.

The waves in the upper layersare translated into cyclones andanticyclones at ground level.

The velocity creates adifference in air concentrationbetween different systems.

The jet streamgenerates air rotation,or vorticity.

HADLEY CELLWarm air ascends in the equatorial regionand moves toward the middle latitudes, inwhich the Sun's average angle of incidence islower than in the tropics.

Winddirection

Isobars

Equator

Rotation ofthe Earth

Westerlies

Polareasterlies

Jet-streamcurrents

Low-pressurearea

High-pressurearea

The atmosphere is a dynamic system. Temperature changes and the Earth'smotion are responsible for horizontal and vertical air displacement. Herethe air of the atmosphere circulates between the poles and the Equator

in horizontal bands within different latitudes. Moreover, the characteristicsof the Earth's surface alter the path of the moving air, causing zones ofdiffering air densities. The relations that arise among these processesinfluence the climatic conditions of our planet.

Convergence Divergence Convergence Divergence

CycloneAnticyclone

Minimum wind velocity(convergence)

Maximum wind velocity(divergence)High-altitude

air flow (jet stream)

Surfaceair flow

Jet stream

CycloneAnticyclone

WEATHER SYSTEMS ANALYSISThe continuous lines are isobars (in this case, in theSouthern Hemisphere), imaginary lines that connectpoints of equal pressure. They show depressions—centers of low pressure relative to the surroundings—and an anticyclone, a center of high pressure.

FERREL CELLA part of the air in theHadley cells follows itscourse toward the polesto a latitude of 60° Nand 60° S.

POLAR CELLAt the poles, cold air descendsand moves toward the Equator.Atmospheric Dynamics

--

+

--

STRATOSPHERE

Jet stream

TROPOSPHERE

EARTH'SSURFACE

10 miles (16 km)

6 miles(10 km)

JET STREAM

Discovered in the 19thcentury through the use ofkites. Airplanes can shortentheir flying time by hitchinga ride on them. Their pathsare observed to help predictthe weather.

Velocity

Length

Width

55 to 250 miles perhour (90-400 km/h)

1,000 to 3,000 miles(1,610-4,850 km) 1 to 3 miles (1.6-4.8 km)

Subtropical jetstream

Polar jetstream

The masses ofcold air losetheir mobility.

High and Low PressureWarm air rises and causes a low-pressurearea (cyclone) to form beneath it. As the air

cools and descends, it forms a high-pressure area(anticyclone). Here the air moves from ananticyclonic toward a cyclonic area as wind. Thewarm air, as it is displaced and forced upward,leads to the formation of clouds.

Equator

+

+

+

--

--

+

++

--

--

----

----

FRANCE

GERMANYBELARUS

POLAND

UKRAINEBonn PragueKraków

Kiev

Collision


Cool air

Cool air

Warm air

Warm airCold air

Cold air

A long Rossby wave developsin the jet stream of the hightroposphere.

1 The Coriolis effectaccentuates the wave actionin the polar air current.

2 The formation of a meander of warmand cold air can provide the conditionsneeded to generate cyclones.

3Rossby WavesLarge horizontal atmospheric waves that areassociated with the polar-front jet stream.They may appear as large undulations in thepath of the jet stream. The dynamics of theclimatic system are affected by these wavesbecause they promote the exchange ofenergy between the low and high latitudesand can even cause cyclones to form.

OCCLUDED FRONTSWhen the cold air replaces the cool airat the surface, with a warm air massabove, a cold occlusion is formed. Awarm occlusion occurs when the cool airrises above the cold air. These fronts areassociated with rain or snow, cumulusclouds, slight temperature fluctuations,and light winds.

STATIONARY FRONTSThese fronts occur when there is noforward motion of warm or cold air—thatis, both masses of air are stationary. Thistype of condition can last many days andproduces only altocumulus clouds. Thetemperature also remains stable, and thereis no wind except for some flow of airparallel to the line of the front. Therecould be some light precipitation.

Entire ContinentsFronts stretch over large geographic areas.In this case, a cold front causes stormperturbations in western Europe. But to theeast, a warm front, extending over a widearea of Poland, brings light rain. These frontscan gain or lose force as they move over theEarth's surface depending on the globalpressure system.

Severe imbalancein the cold front

Very dense cloudsthat rise to aconsiderable altitude

Thick rainclouds

A barely noticeableimbalance of a warm front

Rain belowthe front

Warm FrontsThese are formed by the action of winds. Amass of warm air occupies a place formerly

occupied by a mass of cold air. The speed of the coldair mass, which is heavier, decreases at ground levelby friction, through contact with the ground. Thewarm front ascends and slides above the cold mass.This typically causes precipitation at ground level.Light rain, snow, or sleet are typically produced, withrelatively light winds. The first indications of warmfronts are cirrus clouds, some 600 miles (1,000 km) infront of the advancing low pressure center. Next,layers of stratified clouds, such as the cirrostratus,altostratus, and nimbostratus, are formed while thepressure is decreasing.

Behind the cold front,the sky clears and thetemperature drops.

The cold front forces the warmair upward, causing storms.

There could beprecipitation in the areawith warm weather.

Cold front

A warm front can be 125 miles (200 km)long. A cold front usually covers about60 miles (100 km). In both cases, the

altitude is roughly 0.6 mile (1 km).

125 miles(200 km)

As the clouds extendover a region, theyproduce light rain or snow.

The mass of cold air takes the formof a retreating wedge, which hasthe effect of lifting the warm air asit moves over the mass of cold air.

If thewarm front

moves faster thanthe retreating wedge of

cold air, the height of theadvancing warm frontcontinues to increase.

Surface warm front

KEY

Surface cold front

Cool air

Cold front Warm front

Warm airCold air

When two air masses with different temperatures and moisture content collide, theycause atmospheric disturbances. When the warm air rises, its cooling causes watervapor to condense and the formation of clouds and precipitation. A mass of warm

and light air is always forced upward, while the colder and heavier air acts like a wedge. Thiscold-air wedge undercuts the warmer air mass and forces it to rise more rapidly. This effect can cause variable, sometimes stormy, weather.

Cold FrontsThese fronts occur when cold air is moved by thewind and collides with warmer air. Warm air is

driven upward. The water vapor contained in the air formscumulus clouds, which are rising, dense white clouds. Coldfronts can cause the temperature to drop by 10° to 30° F(about 5°-15° C) and are characterized by violent andirregular winds. Their collision with the mass of ascendingwater vapor will generate rain, snow flurries, and snow. Ifthe condensation is rapid, heavy downpours, snowstorms(during the cold months), and hail may result. In weathermaps, the symbol for a cold front is a blue line oftriangles indicating the direction of motion.

WEATHER AND CLIMATE 1716 CLIMATOLOGY

Colors in the SkyA

natural spectacle of incomparable beauty, the auroras areproduced around the magnetic poles of the Earth by the activityof the Sun. Solar wind acts on the magnetosphere, which is a

part of the exosphere. In general, the greater the solar wind, the moreprominent the aurora. Auroras consist of luminous patches and columnsof various colors. Depending on whether they appear in the north orsouth, they are called aurora borealis or aurora australis. The auroraborealis can be seen in Alaska, Canada, and the Scandinavian countries.

BOW SHOCK WAVE

MAGNETOTAIL OVAL AURORA

THE SUN emits solarwinds, whichcause seriousdamage and anincrease intemperature.

SOLAR WIND

THE POLES The auroras are morenoticeable near the poles;they are called auroraborealis in the NorthernHemisphere and auroraaustralis in the SouthernHemisphere.

THE EARTH The Earth'smagnetosphere isresponsible forprotecting theplanet from thedeadly and harmfulsolar winds.

10-20minutesduration of thephenomenonThe amount of light emittedoscillates between 1 and 10 millionmegawatts, equivalent to theenergy produced by 1,000 to10,000 large electric power plants.

620miles(1,000 km)is how long an aurora can be.From space it will look like acircle around one of themagnetic poles of the Earth.

THEY BECOMEEXCITEDAfter the shock, the atomsreceive a significantadditional energetic chargethat will be released in theform of photons (light).

2 THEY GENERATE LIGHTDepending on the altitude and thevelocity where the shock is produced,the aurora displays different colors.Among the possibilities are violet,green, orange, and yellow.

3ELECTRONS COLLIDE WITHMOLECULESThe oxygen and nitrogen moleculesreceive the impact of the particlesfrom the Sun. This occurs in themagnetosphere (exosphere).

1

310-370 MILES(500-600 KM)

55-300 MILES (90-500 KM)

0-6 MILES (0-10 KM)

Nitrogen atomsand molecules emit violet light.

Sodium atomsand moleculesemit a yellowishorange light.

MAGNETOSPHERE(EXOSPHERE)

MESOSPHERE

TROPOSPHERE

Oxygen atomsand moleculesemit green light.

The auroras are the result ofthe shock produced as ions

coming from the Sun make contactwith the magnetic field of the Earth.They appear in different colors

depending on the altitude at whichthey are produced. Moreover, theydemonstrate the function of themagnetosphere, which protects theplanet against solar winds.

How They Are Produced

Solar WindsThe Sun emits radiation, continuously andin all directions. This radiation occurs as a

flow of charged particles or plasma, whichconsists mainly of electrons and protons. Theplasma particles are guided by the magneticfield of the Sun and form the solar wind, whichtravels through space at some 275 miles persecond (450 km/s). Particles from the solarwind arrive at the Earth within four or five days.

A satellite image of the aurora borealis

NORTH POLE

MONSOONS 28-29

GOOD FORTUNE AND CATASTROPHE 30-31

THE ARRIVAL OF EL NIÑO 32-33

THE EFFECTS OF EL NIÑO 34-35

Surface Factors

Among meteorologicalphenomena, rain plays a veryimportant role in the life ofhumans. Its scarcity causesserious problems, such as

droughts, lack of food, and an increase ininfant mortality. It is clear that an excessof water, caused by overabundant rain orthe effects of gigantic waves, is alsocause for alarm and concern. In

Southwest Asia, there are frequenttyphoons and torrential rains duringwhich millions of people lose theirhouses and must be relocated to moresecure areas; however, they still run the

risk of catching contagious diseases suchas malaria. The warm current of El Niñoalso affects the lives and the economy ofmillions of people.

LIVING WATER 20-21

OCEAN CURRENTS 22-23

AN OBSTACLE COURSE 24-25

THE LAND AND THE OCEAN 26-27

VIETNAM, DECEMBER 1991The intense monsoon rainscaused severe flooding in vastregions of Cambodia, Vietnam,Laos, and Thailand.

WATER AVAILABILITY(cubic feet [cu m] per capita/year)

Less than 60,000 cu ft(1,700 cu m)

60,000-175,000 cu ft(1,700-5,000 cu m)

More than 175,000 cu ft(5,000 cu m)

Less than 50% of thepopulation

SouthAmerica

Europe

Africa

Oceania

NorthAmerica Asia

PacificOcean

AtlanticOcean

ArcticOcean

PacificOcean

IndianOcean

WHERE IT IS FOUNDA small percentage isfreshwater; most of itis salt water.

FRESHWATER

Undergroundwater 1%

Ice2%

0.03%water on

the surfaceand in the

atmosphere

Lakes0.029%

Atmosphere0.001%

Rivers0.00015%

FRESHWATER

3 %SALT WATER

97 %The water in the oceans, rivers, clouds, and rain is in constant motion. Surface water evaporates,water in the clouds precipitates, and this precipitation runs along and seeps into the Earth.Nonetheless, the total amount of water on the planet does not change. The circulation and

conservation of water is driven by the hydrologic, or water, cycle. This cycle begins with evaporation ofwater from the Earth's surface. The water vapor humidifies as the air rises. The water vapor in the air coolsand condenses onto solid particles as microdroplets. The microdroplets combine to form clouds. When thedroplets become large enough, they begin to fall back to Earth, and, depending on the temperature of theatmosphere, they return to the ground as rain, snow, or hail.

Living Water

GASEOUS STATEThe rays of the Sunincrease the motion of atmospheric gases.The combination ofheat and windtransforms liquid waterinto water vapor.

FORMATION OF DROPLETSThe molecules of watervapor decrease theirmobility and begin to collect on solid particles suspended in the air.

LIQUID STATEA rise in temperature increases thekinetic energy of the molecules,which breaks the hydrogen bonds.

SOLID STATEThe molecules have very littlemobility because of the greatnumber of bonds they establishwith hydrogen atoms. Theyform snow crystals.

20 SURFACE FACTORS

1. EVAPORATIONThanks to the effects of theSun, ocean water is warmedand fills the air with watervapor. Evaporation fromhumid soil and vegetationincreases humidity. The resultis the formation of clouds.

2. CONDENSATIONIn order for water vapor to condenseand form clouds, the air must containcondensation nuclei, which allow themolecules of water to formmicrodroplets. For condensation tooccur, the water must be cooled.

3. PRECIPITATIONThe wind carries the clouds toward thecontinent. When the humid air cools, itcondenses and falls as rain, snow, or hail.

72OF WATER FALL EACH DAY INTHE FORM OF PRECIPITATION.

cubicmiles

cubicmiles

TRANSPIRATIONPerspiration is a natural processthat regulates body temperature.When the body temperaturerises, the sweat glands arestimulated, causing perspiration.

OCEAN

DISCHARGE AREA

RIVER

CLOUDS

WIND

LAKE

INFILTRATION

PERMEABLELAYERS

IMPERMEABLELAYERS

Undergroundaquifers

RAIN

SNOWCONTRIBUTION OF LIVINGBEINGS, ESPECIALLY PLANTS, TO

10% THE WATERIN THEATMOSPHERE

THE HUMANBODY IS65% WATER.

All themoleculesof water arefreed.

Root cells

Nucleus

The water vaporescapes viamicropores in theleaves' surface.

3

The water ascendsvia the stem.2

The rootabsorbs water.

Some of the moleculesare set free.

The majority ofthem remainbonded.

1

6. RETURN TO THE OCEANThe waters return to the ocean, completingthe cycle, which can take days for surfacewaters and years for underground waters.

5. UNDERGROUND CIRCULATIONThere are two kinds, both ofwhich are gravity driven. Thefirst occurs in a shallow zone, inkarstic rock such as limestone,and consists of a downward flow.The second occurs in aquifers,where interstitial water fills upthe pores of a rock.

4. RUNOFFWater in liquid form runs offthe surface of the terrain viarivers and valleys. In climatesthat are not especially dry, thisphenomenon is the principalgeologic agent of erosion andtransport. Runoff is reducedduring times of drought.

300yearsTHE AVERAGE LENGTH OFTIME THAT A WATERMOLECULE REMAINS IN THEUNDERGROUND AQUIFERS

340OF WATER CIRCULATE IN THETERRESTRIAL HYDROSPHERE.

WEATHER AND CLIMATE 21

AQUIFERS

Access to potable water

Indian

Ocean

Pacific

Ocean

antic

ean

North Equatorial Countercurrent

South Equatorial Current

Western AustraliaCurr

ent

Wes

tAustra

lian

Curre

nt

Ben

gu

ela

Cu

rren

t

Agulhas

Cur

rent

uatorial Current


t

South

Equa

toria

l Current

Oya Current

Ku

rosh

io

Equatorial Countercurrent

currentEquatorial Countercurrent

Antarctic Circumpolar Current

a C u r r e n t

nt

rador

Cu

rren

t

North Atlantic Current

Arctic circulati

ng

syst

em

Antarctic circulating system

Pacific

Ocean

Pacific

Ocean

Atlantic

Ocean

Atlantic

Ocean

Cal

iforn

iaCurr

ent

North Pacific Current

PeruvianCurrent

Falkland

Current

Bra

z il

Cu

rre

nt


North Equatorial Counterc

urr

ent

South Equatorial Current

South Equatorial Cu



Antarctic Circumpolar Current

A l a s k a C u r r e

Gulf Stream

Can

ary

Curren

t

Labra

dorC

urr

ent

An

Ocean water moves as waves, tides, and currents. There aretwo types of currents: surface and deep. The surfacecurrents, caused by the wind, are great rivers in the ocean.

They can be some 50 miles (80 km) wide. They have a profoundeffect on the world climate because the water warms up nearthe Equator, and currents transfer this heat to higher latitudes.Deep currents are caused by differences in water density.

Ocean Currents

TIDES AND THE CORIOLIS EFFECTThe Coriolis effect, which influencesthe direction of the winds, drives thedisplacement of marine currents.

SUBPOLAR ARCTICCIRCULATING SYSTEMFor the last five decades,these currents have beenshown to be undergoingdramatic changes.

EKMAN SPIRALexplains why thesurface currents anddeep currents areopposite in direction.

DEEP CURRENTS

have a vital function of carryingoxygen to deep water. This permitslife to exist in deep water.

THE FOUR SEASONSOF A LAKE

Because of the physicalproperties of water, lakesand lagoons have a specialseasonal circulation thatensures the survival of livingcreatures.

GEOSTROPHIC BALANCEThe deflection caused by the Coriolis effect onthe currents is compensated for by pressuregradients between cyclonic and anticyclonicsystems. This effect is called geostrophic balance.

Coriolisforce

Low pressureSubpolar low pressure

Currents in theNorthernHemisphere travelin a clockwisedirection.

In the SouthernHemisphere, thecurrents travel in acounterclockwisedirection.

High pressureSubtropical high-pressure center

Pressuregradient

Winds

22 SURFACE FACTORS WEATHER AND CLIMATE 23

THE INFLUENCE OF THE WINDS

HOW CURRENTS ARE FORMEDWind and solarenergy producesurface currentsin the water.

1. In the SouthernHemisphere, coastal windspush away the surfacewater so that cold watercan ascend.

Warm surfacewaters

Deep coldwater

Deeplayers

COAST

Subsurfacewatersoccupy the spaceleft by themotion of thesurface waters.

This slow ascent of deepwater is called a surge. Thismotion is modified by the

Ekman spiral effect.

Wind energy istransferred to the waterin friction layers. Thus,the velocity of thesurface water increasesmore than that of thedeep water.

The Coriolis effectcauses the direction ofthe currents to deviate.The surface currentstravel in the oppositedirection of the deepcurrents.

64° F (18 °C)

61° F (16 °C)

57° F (14 °C)

54° F (12 °C)

Near Greenland, the North Atlanticwater sinks, and the colder andmore saline wateris pushedsouthward.

GulfStream

Summerstratification

77 °

75 °

64 °

55 °

46 °

43 °

41 °

41 °

46 °

46 °

41 °

32 °35 °37 °

39 °37 °

39 °

Epilimnion

Thermocline

Hypolimnion

Fahrenheit

Ocean conveyor belt

Warm Cold

Winter mixture

Spring mix

Autumn mixture

1 Warm surface waterfrom the Gulf Streamreplaces the cold waterthat is sinking.

2

SUMMERStable summer temperaturesprevent vertical circulation in thebody of water of the lagoon.

AUTUMNTemperature decrease andtemperature variations generatea mixing of the surface and deepwaters.

WINTERWhen the water reaches 39° F(4° C), its density increases. Thatis how strata of solid water onthe surface and liquid waterunderneath are created.

SPRINGThe characteristics of water onceagain initiate vertical circulation inthe lake. Spring temperatures leadto this circulation.

Warm currentCold current

2.

The Effect of the Andes Mountains

1. HUMID WINDSIn the mountains, the predominantwinds are moisture-laden and blow inthe direction of the coastal mountains.

The mountains are geographical features with a great influence on climate. Winds laden withmoisture collide with these vertical obstacles and have to rise up their slopes to pass overthem. During the ascent, the air discharges water in the form of precipitation on the

windward sides, which are humid and have dense vegetation. The air that reaches the leewardslopes is dry, and the vegetation usually consists of sparse grazing land.

An Obstacle CourseMountain

Everest

Aconcagua

Dhaulagiri

Makalu

Nanga Parbat

Kanchenjunga

Ojos del Salado

Kilimanjaro

MAJOR MOUNTAIN RANGES

HOW OBSTACLES WORK

TYPES OF OROGRAPHICAL EFFECTS

VEGETATION

Elevation

29,035 feet (8,850 m)

22,834 feet (6,960 m)

26,795 feet (8,167 m)

27,766 feet (8,463 m)

26,660 feet (8,126 m)

28,169 feet (8,586 m)

22,614 feet (6,893 m)

19,340 feet (5,895 m)

13,000(4,000)

10,000(3,000)

6,500(2,000)

3,000(1,000)

0 feet (0 m)

HIGH LEVEL OFPOLLUTION INSANTIAGOPartly because it isthe most urbanizedand industrialized cityof Chile, the capital,Santiago, facesserious pollutionproblems. In addition,it is located in avalley withcharacteristics thatdo not help dispersethe pollutionproduced by vehiclesand factories.

This drawing showsthe coast and theAndes near Santiago,Chile, at UspallataPass.

Moist adiabaticgradientThe temperaturedecreases 1° F (0.6° C) for every300 feet (100 m).

Dew point, orcondensation point

Dry adiabaticgradientThe temperaturedeclines 1.8° F (1° C) every 300feet (100 m).

Temperature (in °F [°C])

-40 to -4 (-40 to -20)

-4 to 14 (-20 to -10)

14 to 32 (-10 to 0)

Greater than 32 (0)

Composition

Ice crystals

Supercooledwater

Microdropletsof water

Drops ofwater

IN THE CLOUD

SNOW RAIN

16,400(5,000)

13,000(4,000)

10,000(3,000)

6,500(2,000)

3,000(1,000)

Surface

Height infeet (m)

24 SURFACE FACTORS

2. ASCENT AND CONDENSATIONCondensation occurs when a mass of air coolsuntil it reaches the saturation point (relativehumidity 100 percent). The dew point rises whenthe air becomes saturated as it cools and thepressure is held constant.

3. PRECIPITATIONA natural barrier forces theair to ascend and cool. Theresult is cloud formationand precipitation.

4. DESCENDINGWINDA naturalbarrier forcesthe air todescend andwarm up.

Western slopesreceive most of the moisture, whichleads to the growth of pine and othertrees of coastal mountain ranges.

Eastern slopesThe rays of the Sun fall directly uponthese areas, making them more arid.There is little or no vegetation.

Obstacles, such as buildings,trees, and rock formations,decrease the velocity of thewind significantly and oftencreate turbulence around them.

CLASSIC SCHEMEThe more humid zoneis at the top.

VERY HIGHThis is produced onmountains above16,400 feet (5,000 m)in height.

The most humid area ishalfway up the slope,on the windward side.

UNEVENMOUNTAINSIDEThe most humidarea is at the top ofthe leeward slope.

It runs parallel to the Pacific Ocean,from Panama to southern Argentina.It is 4,500 miles (7,240 km) longand 150 miles (241 km) wide.

19,700 feet(6,000 m).

ANDES MOUNTAIN RANGEhas altitudes greater than

FRONT VIEW Rotational flow

Flow and counterflowPLAN VIEW

A R G E N T I N A

C H I L E

Drops of super-cooled watercombine to form ice crystals.

The crystals grow in size.

While they arefalling, they combinewith other crystals.

The microdropletsincrease in size andfall because ofgravity.

When they fall,these drops collidewith smaller ones.

Successivecollisions increasethe size of thedrops.

90° F(32° C)

72° F(22° C)

54° F(12° C)

36° F (2° C)

27° F (-3° C)

18° F (-8° C)

Viña delMar

Santiago,Chile

Valparaíso

PACIFICOCEAN

COASTALMOUNTAIN RANGE

INTERMEDIATEDEPRESSION

RockyMountains

Appalachians

Alps

Urals

Himalayas

Andes

Tundra. Its rate of growthis slow and only during thesummer.

Taiga. The vegetation isconifer forest.

Mixed forest. Made up ofdeciduous trees and conifers.

Chaparral. Brush withthick and dry leaves.

Grazing. Thicketspredominate: low, perennialgrazing plants with anherbaceous appearance.

Area affected byprecipitation

DRY HUMIDSWinds Winds


ALBEDO -ENERGYABSORBED-+

80%RECENT SNOW

75%THICK CLOUDS

50%LIGHT CLOUDS

3-5%WATER (WHENTHE SUN IS HIGH)

25%WET SAND

15%ALBEDO OFMEADOWS

1.7-14%FORESTS

The Land andthe Ocean

The Sun heats the soilof the valley and thesurrounding air, whichascends by convection.

The air is cooled as it ascends,becomes more dense, anddescends. Then it heats upagain and repeats the cycle.

They absorb a significantamount of heat but remain coolbecause much energy is usedto evaporate the moisture.

The air tends todescend in forestedand rural areas.

During the night, the cityslowly releases heat that wasabsorbed during the day.

The flows tendtoward equilibrium.

HEAT ISLANDSCities are complex surfaces. Concreteand asphalt absorb a large quantity ofheat during sunny days and release itduring the night.

WARM AIR WHIRLWINDSIntense heat on the plains can generate a hot, spiral-formed column of air sometimes more than 300 feet(100 m) high.

ON THE LANDDuring the day, the land heats upmore rapidly than the ocean. Thewarm air rises and is replaced bycooler air coming from the sea.

Because it isopaque, the heatstays in thesurface layers,which areheated andcooled rapidly.

When nightfalls, the land,which was hot,cools rapidly.

When nightfalls, the wateris lukewarm(barely adegree morethan the land).

The heatpenetrates intodeeper layersthanks to thetransparency ofthe water. Apart of the heatis lost inevaporation ofthe water.

LAND

WATER

COLD AIR

WARM AIR

IN THE OCEANFrom the coast, the ocean receivesair that loses its heat near thewater. As a result, the colder airdescends toward the sea.

IN THE OCEANThe loss of heat from the water isslower.

2. ON THE LANDDuring the evening, the land radiatesaway its heat more rapidly than thewater. The difference in pressuregenerated replaces the cold air ofthe coast with warm air.

In the interior of a landmass,there is a wide variation ofdaily temperatures, while onthe coasts, the influence ofthe ocean reduces thisvariation. This continentalityeffect is quite noticeable inthe United States, Russia,India, and Australia.

Isotherms in a typical city

Continentality index

Daily variation of temperaturesin the United States

Less More

26 SURFACE FACTORS

WINDS OF THE MOUNTAINSAND VALLEYS

COASTAL BREEZES

CONTINENTALITY

1

Cold air currents descend from themountainside toward the floor ofthe valley, which is still hot.

1

2

The air currentsare heated and ascend byconvection. When they rise, theycool and once again descend along themountainside.

MOUNTAINSIDE

VALLEY

VALLEY

WARM-AIRFLOW

COLD-AIRFLOW

STRONG WIND

MILD WIND

SLOPE

2

82° F84° F84° F82° F

84°F 86°F 88° F82°F 90°F

90°F 86°F 82° F88°F 84°F

82° F84° F84° F82° F

81° F 81° F

1 Strong, high-speed winds move ontop of weaker winds and cause theintermediate air to be displaced likea pencil on a table.

1 A powerful aircurrent lifts thespiral.

2

LAND

WATER

COLD AIR

WARM AIR


Temperature distribution and,above all, temperaturedifferences very much depend

on the distribution of land and watersurface. Differences in specific heatmoderate the temperatures of regionsclose to great masses of water. Waterabsorbs heat and releases it moreslowly than the land does, which iswhy a body of water can heat or coolthe environment. Its influence isunmistakable. Moreover, thesedifferences between the land and thesea are the cause of the coastal winds.In clear weather, the land heats upduring the day, which causes the air torise rapidly and form a low-pressurezone. This zone draws marine breezes.

KEY

Chinook WINDSThese winds are dry and warm, sometimes quite hot,occurring in various places of the world. In the westernUnited States, they are called chinooks and are capableof making snow disappear within minutes.

MOUNTAIN WINDS

Humid winds are lifted overthe slopes, creating cloudsand precipitation on thewindward side. These arecalled anabatic winds.

The dry and cool winddescends down themountain slope on theleeward side. It iscalled katabatic.

WINDWARD

LEEWARD

Autan windBergBoraBrickfielderBuran HarmattanLevantMistralSanta AnaSiroccoTramontanaZonda

Winds Characteristics Location

Dry and mildDry and warmDry and coldDry and hotDry and coldDry and coolHumid and mildDry and coldDry and hotDry and hotDry and coldDry and mild

Southwestern FranceSouth AfricaNortheastern ItalyAustraliaMongoliaNorth AfricaMediterranean regionRhône valleySouthern CaliforniaSouthern Europe and North AfricaNortheast SpainWestern Argentina

Factories and vehicles emitlarge amounts of heat intothe atmosphere.

The strong humid winds that usually affectthe tropical zone are called monsoons, anArabic word meaning “seasonal winds.”

During summer in the Northern Hemisphere, theyblow across Southeast Asia, especially the Indianpeninsula. Conditions change in the winter, and thewinds reverse and shift toward the northernregions of Australia. This phenomenon, which isalso frequent in continental areas of the UnitedStates, is part of an annual cycle that, as a resultof its intensity and its consequences, affects thelives of many people.

STORMS ON THECONTINENT

The climate in Indiaand Bangladesh is very

hot and dry. When humidand cool winds come in from

the ocean, they cause torrentialrains in these regions.

FROM THE OCEAN TO THECONTINENTThe cool and humid airfrom the ocean blowstoward the continent,which is quite hot and dry.

BARRIERSThe humid winds are

deflected towardthe northeast by

two mountain chains:the Himalayas and the

Ghat mountains. This zoneenclosed by the mountains

is the main one affectedby the monsoons.

12

OCEAN STORMSA cyclone located in the ocean drawsthe cold winds from the continent andlifts the somewhat warmer and morehumid air, which returns toward thecontinent via the upper layers of theatmosphere.

FROM THE CONTINENT TO THE OCEANThe masses of cold and dryair that predominate on thecontinent are displacedtoward the ocean,whose waters arerelatively warmer.

How monsoons arecreated in India

Monsoons

28 SURFACE FACTORS

AREAS AFFECTED BY MONSOONSThis phenomenon affects the climates in low latitudes, fromWest Africa to the western Pacific. In the summer, themonsoon causes the rains in the Amazon region and innorthern Argentina. There in the winter rain is usually scarce.

THE MONSOON OF NORTH AMERICAPre-monsoon. Month of May. Monsoon. Month of July.

Predominantdirection of thewinds during themonth of July

Limit of theIntertropicalConvergenceZone (ITCZ)

Limit of theintertropicalconvergence

Cold land

Warmland

Bay ofBengal

Bay ofBengal

Rays ofthe Sun

Angle ofincidence ofthe Sun'srays

ArabianSea

ArabianSea

Northern HemisphereIt is winter. The rays of theSun are oblique, traveling alonger distance throughthe atmosphere to reachthe Earth's surface. Thusthey are spread over alarger surface, so theaverage temperature islower than in the SouthernHemisphere.

Southern HemisphereIt is summer. The rays ofthe Sun strike the surfaceat a right angle; they areconcentrated in a smallerarea, so the temperatureon average is higher than inthe Northern Hemisphere.

The land is cold, so nearthe ground the breezeblows toward the ocean.

The Earth is hot, andtherefore the air rises andis replaced in the lowerlayers by cool breezes thatblow in from the sea. Themeeting of the two breezescauses clouds and rain onthe continent.

The sea is cold becausethe rays of the Sun heatup the water moreslowly than the land.The cool air from theocean blows toward thecoast, toward areasthat are warmer.

The sea is a little warmerthan the land; therefore,the humid air rises. Thecool air colliding with itcauses clouds and rain.

N

S

INTERTROPICAL INFLUENCE

End of themonsoon

Beginning ofthe monsoon

Cold anddry winds

Cold andhumidwinds

Cyclone(lowpressure)

Anticyclone(highpressure)

Cross section (enlarged area)

Descent of the airfrom high altitudes

Descent of the airfrom high altitudes

Transport ofwater vapor

Western SierraMadre

Transport ofwater vapor

Rays of the Sun

Pacific Ocean Gulf of California Gulf of Mexico

THE CONTINENT COOLSAfter the summer monsoon, the rains stop andtemperatures in Central and South Asia begin to drop.Winter begins in the Northern Hemisphere.

1

33

2

THERMALDIFFERENCEBETWEEN THE LANDAND THE OCEAN


The circulation of the atmosphere between thetropics influences the formation of monsoonwinds. The trade winds that blow toward theEquator from the subtropical zones are pushed bythe Hadley cells and deflected in their course bythe Coriolis effect. Winds in the tropics occurwithin a band of low pressure around the Earthcalled the Intertropical Convergence Zone (ITCZ).When this zone is seasonally displaced in thewarm months of the Northern Hemisphere towardthe north, a summer monsoon occurs.

WEATHER AND CLIMATE 3130 SURFACE FACTORS

The monsoons are a climatic phenomenon governing the life and the economy of one of the mostdensely populated regions of the planet, especially India. The arrival of the intense rains iscelebrated as the end of a season that might have been extremely dry, but it is also feared. The

flooding at times devastates agriculture and housing. The damage is even greater because of thelarge population of the region. Therefore, anticipating disaster and taking precautions, such asevacuating areas prone to flooding, are part of the organization of agricultural activity, which thrives in periods of heavy rains, even in fields that are flooded.

Good Fortune and Catastrophe

Precipitation(in inches [mm])

Very humid

Extreme

humidity

Humid

Normal

Very dry

Extremely

dry

16 (400)

8 (200)

4 (100)

2 (50)

1 (25)

0.4 (10)

0.04 (1)

0 (0)

OVERFLOWING RIVERSThe valley that connects theGanges with the Brahmaputrain Bangladesh is the mostafflicted by floods caused bythese rains. The rains destroyharvests and property.

UNDERWATER HARVESTThe mud increases the fertilityof the soil, which compensatesfor the losses. The accumulationof humid sand is later used inthe dry season. Rice is a grainthat grows in fields that areunderwater.

In June 2006The tragic outcome of themonsoon in South Asia

Nueva Delhi

~49DEATHS on June 16, 2006

21DEATHS On June 16,2006

~1 million PEOPLE STRANDED BY STORMSIN BANGLADESH

~212During the month of June 2006.Most of them were electrocuted bylightning during electrical storms.

BANGLADESHI N D I A

Kerala

Dhaka

Uttaranchal

DEATHS ININDIA

INDIA ANDBANGLADESH

Total population

1.25 billion

5.5 (140)

0 (0)

-7 (-180)Inches (mm)

-7 -5.5 -4 -2 -0.08 0.08 2.4 4 5.5 7(-180) (-140) (-100) (-50) (-20) (20) (60) (100) (140) (180)

The hydrosphere and the atmosphere interact and establish a dynamic thermal equilibriumbetween the water and the air. If this balance is altered, unusual climatic phenomena occurbetween the coasts of Peru and Southeast Asia. For example, the phenomenon El Niño or, less

frequently, another phenomenon called La Niña are responsible for atypical droughts and floods thatevery two to seven years affect the routine life of people living on these Pacific Ocean coasts.

The Arrival of El Niño

PeruCurrent

KEY

South Pacificanticyclone

South Atlanticanticyclone

IntertropicalConvergence

Zone

Anticyclone ofthe SouthAtlantic

IntertropicalConvergenceZone

5.4° F (3° C)

2° C

1° C

0

-1° C

-2° C

EL NIÑOWarmerthan normal Average intensity

Intense

LA NIÑAColder thannormal

NORMAL

Anticyclone of the SouthAtlantic

IntertropicalConvergenceZone

Anticyclone (high-pressure center)

Cold Mild Warm

TRADEWINDS

Peru Current

The anticyclone of the South Pacificis displaced towardthe south.

TRADE WINDS(weak)

Normal Conditions El Niño (the warm phase of ElNiño/Southern Oscillation [ENSO])DURATION 9 to 18 months

La Niña (cold ENSO)DURATION: 9 to 18 monthsFREQUENCY: Every 2 to 7 years

32 SURFACE FACTORS

Climatic equilibriumNormally the coasts ofSoutheast Asia lie in an areaof low pressure and highhumidity, which causes heavyprecipitation. On theAmerican coast of the SouthPacific, the climate is verydry by comparison.

1

Without trade windsIn periods that can vary from two to seven years, thetrade winds that push thewarm water toward the westcan be sharply reduced or evenfail to occur. As a result, theentire mass moves toward theSouth American coast.

1OvercompensationThe return of normal conditions after ElNiño can be (although not necessarily) thepreamble to an inverse phenomenon calledLa Niña. As a consequence of SouthernOscillation pressure levels, the trade winds become stronger than normal.

1Climate inversionFor six months, thenormal climaticconditions are reversed.The temperature of thewater and air increasesalong the coasts of Peruand Ecuador, and thehumidity causes heavy rains.

2

A cold currentThe total disruption ofthe masses of warmwater off the west coastof South America alsogenerates colder surfacetemperatures thannormal along with highpressure and decreasedhumidity.

2Severe droughtThe effects of La Niña are lesssevere than those of El Niño.Also, the shorter its duration,the more intense it is. Ittypically begins about halfwaythrough the year andintensifies at the end of theyear before weakening aroundthe beginning of the new year.In the Caribbean, La Niñacauses an increase in humidity.

3El Niño makes itself felt.Southeast Asia suffers a greatdrought, an increase of pressure,and a decrease in temperature.On the South American coast,strong winds and storms occur inzones that are usually dry; thereis flooding and changes in theflora and fauna.

3

A largemass of warmwater accumulates on thewestern coasts of the SouthPacific and is sustained by thepersistence of the trade windsat the ocean surface.

Warmsurfacewaters Warm

surfacewaters

Warmsurfacewater

Cold surfacewater and deep

water

Upwellingcold water

Cold deepwaters

Warm coastsBecause great masses of warmwater permanently flowtoward the coasts of Indonesiaand New Guinea, they areabout 14° F (8° C) warmerthan the South Americancoast, where there is also anupwelling of cold water fromthe ocean floor.

2

Trade windsThese relatively constantwinds push the waters of thePacific Ocean from east towest. Between the coasts ofIndonesia and those ofwestern South America, thereis on average a 2 foot (0.5 m)difference in sea level.

SURFACE TEMPERATURE OF THE OCEANThe graphic shows thetemperature variationscaused by the SouthernOscillation in the wateralong the coast of Peru.This graphic illustrates thealternation of the El Niñoand La Niña phenomenaover the last 50 years.

VIA SATELLITEHow the height of sea

level changed because of theENSO phenomenon.

ON A WORLD SCALEThe temperature of the surface of the ocean

during the El Niño phase of 1997

3

Relatively warm waters replace the upwelling cold water, whichtypically brings a large amount ofvaried fish and other marine life to thesurface off the South American coast.Without this upwelling, fishing outputdrops off rapidly.

The mass of relatively warmwater is displaced completelytoward the western Pacific.The ascent of the cold waterblocks any warm currentthat might go east.

PeruCurrent

Anticycloneof the SouthPacific

TRADEWINDS(strong)

EL NIÑO. April 25, 1997 LA NIÑA. July 11, 1998May 25, 1997 June 25, 1997 September 5, 1997

Images created by the TOPEX/Poseidonsatellite.

Very Cold Normal Cold Warm Hot


The natural warm phenomenon known as El Niño alters the temperature of the water within theeast central zone of the Pacific Ocean along the coasts of Ecuador and Peru. Farmers and fishermenare negatively affected by these changes in temperature and the modification of marine currents.

The nutrients normally present in the ocean decrease or disappear from along the coast because of theincrease in temperature. As the entire food chain deteriorates, other species also suffer the effects anddisappear from the ocean. In contrast, tropical marine species that live in warmer waters can flourish.The phenomenon affects the weather and climate of the entire world. It tends to cause flooding, foodshortages, droughts, and fires in various locations.

The Effects of El Niño

Normal conditionsCold waters, rich in nutrients,ascend from the bottom ofthe sea and provide favorableconditions for the growth ofphytoplankton, the basis ofthe marine food chain.

The phytoplankton promotethe normal development ofmicroorganisms, fish, andother creatures.

Various marine species dieoff for lack of food or mustmigrate to other zones.

During El Niño,the scarcity of cold waterdebilitates the phytoplanktonpopulation and alters themarine food chain.

KEY

A S I A

A F R IC A

O C E A N I A

A M E R IC A

A S I A

A F R IC A

O C E A N I A

A M E R IC A

LA NIÑA from June to August

34 SURFACE FACTORS

Dry andwarm

Dry andcold

Dry

WarmHumid

WarmHumid

ColdHumid

Cold

Humid

ATACAMA,CHILELaguna Blanca Salt MarshLatitude 22° 54´ SLongitude 68° 12´ W

Surface area

Cause

Year

1,200 square miles (3,000 sq km)

Floods caused by El Niño

anomalies

1999

FLOODINGAbnormal flooding caused byEl Niño in the desert regionsof Chile and the laterevaporation of water leavebehind hexagonal deposits ofpotassium nitrate.

Areas Affected EL NIÑO from December to February


ANATOMY OF A HURRICANE 56-57

WHAT KATRINA TOOK AWAY 58-59

FORESIGHT TO PREVENT TRAGEDIES 60-61MeteorologicalPhenomena

WHEN WATER ACCUMULATES 48-49

WATER SCARCITY 50-51

LETHAL FORCE 52-53

DEATH AND DESTRUCTION 54-55

CAPRICIOUS FORMS 38-39

THE RAIN ANNOUNCES ITS COMING 40-43

LOST IN THE FOG 44-45

BRIEF FLASH 46-47

HURRICANE ALERTThis image of Hurricane Elena, capturedby the Space Shuttle on September 1,1985, allowed meteorologists toevaluate its scope before it reached theGulf of Mexico.

Tropical cyclones (calledhurricanes, typhoons, or cyclonesin different parts of the world)cause serious problems and oftendestroy everything in their path.

They uproot trees, damage buildings,devastate land under cultivation, andcause deaths. The Gulf of Mexico is oneof the areas of the planet continuallyaffected by hurricanes. For this reason,

the government authorities organizepreparedness exercises so that thepopulation knows what to do. Tounderstand how hurricanes functionand improve forecasts, investigators

require detailed information from the heartof the storm. The use of artificial satellitesthat send clear pictures has contributedgreatly to detecting and tracking strongwinds, preventing many disasters.

The InsideThe altitude at which clouds areformed depends on the stability of

the air and the humidity. The highest andcoldest clouds have ice crystals. The lowestand warmest clouds have drops of water.There are also mixed clouds. There are 10classes of clouds depending on their heightabove sea level. The highest clouds begin ata height of 2.5 miles (4 km). The mid-levelbegins at a height of 1.2 to 2.5 miles (2-4km) and the lowest at 1.2 miles (2 km) high.

LENTICULAR CLOUDSMountains usually create waves in theatmosphere on their lee side, and on thecrest of each wave lenticular clouds areformed that are held in place by thewaves. Rotating clouds are formed byturbulence near the surface.

CLOUD STREETSThe form of the clouds depends on thewinds and the topography of the terrainbeneath them. Light winds usually producelines of cumulus clouds positioned as ifalong streets. Such waves can be createdby differences in surface heating.

ConvectionThe heat of the Sun warms the air near theground, and because it is less dense than thesurrounding air, it rises.

ConvergenceWhen the air coming from one directionmeets air from another direction, it ispushed upward.

Geographic elevationWhen the air encounters mountains, it is forcedto rise. This phenomenon explains why there areoften clouds and rain over mountain peaks.

Presence of a frontWhen two masses of air with differenttemperatures meet at a front, the warm airrises and clouds are formed.

TYPES OF CLOUDS

Thickness of a storm cloud

1.2 to 5miles (2-8 km)

can be contained in astorm cloud.

150,000tons of water

SPECIAL FORMATIONS

MEANINGNAME

CIRRUS FILAMENT

CUMULUS AGGLOMERATION

STRATUS BLANKET

NIMBUS RAIN

Mild winds

Waves

Wind

Lenticularcloud

Rotating cloud

Lines ofcumulusclouds

Clouds are masses of large drops of water and icecrystals. They form because the water vaporcontained in the air condenses or freezes as it rises

through the troposphere. How the clouds develop dependson the altitude and the velocity of the rising air. Cloudshapes are divided into three basic types: cirrus, cumulus,and stratus. They are also classified as high, medium, andlow depending on the altitude they reach above sea level.They are of meteorological interest because theyindicate the behavior of the atmosphere.

Capricious Forms

38 METEOROLOGICAL PHENOMENA

Stratosphere

Troposphere

Mesosphere

Exosphere

6 miles (10 km)

30 miles(50 km)

Temperature inthe upper part ofthe troposphere

-67° F (-55° C)

The temperature ofthe middle part ofthe troposphere

14° F (-10° C)

Temperature of thelower part of the

troposphere

50° F(10° C)

The layer closest to the Earth and in whichmeteorological phenomena occur, includingthe formation of clouds

Troposphere

HIG

H C

LO

UD

S

ME

DIU

M C

LO

UD

S

2.5 miles

(4 km)

6 miles

(10 km)

LOW

CLO

UD

S

CUMULONIMBUSA storm cloud. It portendsintense precipitation in theform of rain, hail, or snow. Itscolor is white.

STRATUSA low cloud that extends overa large area. It can causedrizzle or light snow. Stratusclouds can appear as a grayband along the horizon.

CUMULUSA cloud that is generallydense with well-definedoutlines. Cumulus cloudscan resemble a mountainof cotton.

NIMBOSTRATUSNimbostratus portends moreor less continuousprecipitation in the form ofrain or snow that, in mostcases, reaches the ground.

STRATOCUMULUSA cloud that is horizontal andvery long. It does not blot out theSun and is white or gray in color.

ALTOCUMULUSA formation of roundedclouds in groups that canform straight or wavy rows

CIRROCUMULUSA cloud formationcomposed of very small,granulated elements spacedmore or less regularly

CIRROSTRATUSA very extensive cloud thateventually covers the whole skyand has the form of atransparent, fibrous-looking veil

CIRRUSA high, thin cloud with white,delicate filaments composedof ice crystals

ALTOSTRATUSLarge, nebulous, compact, uniform,slightly layered masses. Altostratusdoes not entirely block out the Sun.It is bluish or gray.

50 miles(90 km)

300 miles(500 km) The

altitudeat whichit freezes

Turbulentwinds

Anvil-shaped top

Direction ofthe storm

ASCENDINGCURRENT

DESCENDINGCURRENT

HOW THEY ARE FORMEDClouds are formed when the rising air cools tothe point where it cannot hold the watervapor it contains. In such a circumstance, theair is said to be saturated, and the excess

water vapor condenses. Cumulonimbus cloudsare storm clouds that can reach a height of43,000 feet (13,000 m) and contain morethan 150,000 tons of water.

T R O P O S P H E R E

59° F (15° C)

Temperature at theEarth's surface

The year that Britishmeteorologist Luke Howardcarried out the firstscientific study of clouds

1802


0

1.2 miles

(2 km)

0 miles (0 km)

1CONDENSATION NUCLEISalt, dust, smoke, and pollen, among otherparticulates, serve as a surface on whichwater molecules, ascending by convection,can combine and form water droplets.

RAINThe upper part of the cloud spreadsout like an anvil, and the rain fallsfrom the lower cloud, producingdescending currents.

DISSIPATIONThe descending currents arestronger than the ascending onesand interrupt the feeding air,causing the cloud to disintegrate..

L E V E L O F C O N D E N S A T I O N

0.2 inch(5 mm)

0.07 inch (2 mm)

0.04 inch (1 mm)

A DilatationThe molecules of water arefreeΩwater vapor.

B CondensationThe molecules groupthemselves around a condensationnucleus.

The air cools. The watervapor condenses andforms microdroplets of water.

When the air cools, itdescends and is then heatedagain, repeating the cycle.

CoalescenceThe microdropletscontinue tocollide and formbigger drops.

Anvil-shaped

Heavier dropsfall onto alower cloudas fine rain.

Low, thin cloudscontain tinydroplets of waterand thereforeproduce rain.

Collision-Coalescence Via this process,molecules collide and join together toform drops.

C

-22° F (-30° C)

STORMCLOUD

GROWTHThe smallest clouds adhere to oneanother to form larger clouds,increasing their size and height.

The hot airrises.

68° F(20° C)

0.02 inch(0.5 mm)

0.04 inch(1 mm)

When they begin to fall,the drops have a size of0.02 inch (0.5 mm), whichis reduced as they fallsince they break apart.

molecules occupy 1 cubicmillimeter under normalatmospheric conditions.

26,875trillion

2

34 5

MATURATIONMature clouds have very strongascending currents, leading toprotuberances and roundedformations. Convection occurs.T

he air inside a cloud is in continuous motion. This process causes the drops of water or the crystalsof ice that constitute the cloud to collide and join together. In the process, the drops and crystalsbecome too big to be supported by air currents and they fall to the ground as different

kinds of precipitation. A drop of rain has a diameter 100 times greater than a droplet in acloud. The type of precipitation depends on whether the cloud contains drops of water, icecrystals, or both. Depending on the type of cloud and the temperature, the precipitationcan be liquid water (rain) or solid (snow or hail).

The Rain Announces Its Coming


Rock erosionparticulates

Sea-saltparticulates

Sandstormparticulates

Watermolecules

Oxygen

Hydrogen

Forest fireparticulates

Volcanicparticulates

Particulates fromcombustion in

factories and vehicles

0 miles (0 km)

4 miles (7 km)

6 miles(10 km)

0.6-1.2 miles(1-2 km)


HAILPrecipitation in the form of solidlumps of ice. Hail is produced insidestorm clouds in which frozendroplets grow in size as they riseand fall within the cloud.

The drop attaches itself to anucleus or solid particle.

Then the surface ofthe drop freezes.

Condensationnucleus

Drop

Nucleus

Periphery

A HOW CRYSTALSARE FORMED

AVertical air currentscause themicrodroplets toascend and descendwithin the cloud.

BThe droplets freeze, andeach time they are carriedupward in the cloud, theyacquire a new layer of ice.This process, calledaccretion, increases thesize of the hailstone.

A cloud with a greenishtinge or rain with awhitish color canportend ahailstorm.

C

When the hailstonesare too heavy to besupported by theascending aircurrents, they fall tothe ground.

If the dropscrystallize nearthe freezinglevel, they fallin the form ofsleet.

C

SLEET

ASCENDINGWARMCURRENT

WARMASCENDINGCURRENT

SNOWFALL

3 miles(5 km)

-39° F (-39° C)

ICECRYSTAL

2 miles(3 km)

-9° F (-23° C)

0.6 mile(1 km)

19° F (-7° C)

SNOWFLAKE

HOAR FROSTSimilar to frost butthicker. It usuallyforms when thereis fog.

FROSTFrost forms when thedew point of the air isless than 32° F (0° C),and the water vaportransforms directly intoice when it is depositedon surfaces.

Most snowflakes disintegrate beforethey reach the ground. They fall assnowflakes only when the air nearthe ground is very cold.

BThe icecrystalscombine andformsnowflakes.

The record of annual snowfall Mount Rainier, Washington.From February 19, 1971, toFebruary 18, 1972.

10 feet (3.11 m)

CROSS SECTION OF A HAILSTONE

0.2 to 2 inches (5 to 50 mm)

The typical range ofhailstone sizes

The flakesmeasure between 0.04and 0.8 inch (1 and 20 mm).

No two snowflakes areidentical to each other.

Most have six points.

TYPES OF CRYSTALS

Plate

Column

Dendrite

Needle clusters

Layersof ice

32° F (0° C)DEW POINT

DEWWater vapor that condensesduring the night into very smalldrops. The condensation formson surfaces that radiate heatduring the night, such as plants,animals, and buildings.

41° F (5° C)

27° F (-3° C)Temperature of the air

Temperature of the ground

VARIED FORMSSnow crystals can have a variety of shapes; most ofthem have six points, although some have three or 12,and they have hexagonal symmetry in a plane. Theycan also be cubic crystals, but these form underconditions of extremely low temperature in thehighest regions of the troposphere.

HYDROMETEORSDrops of condensed or frozen waterin the atmosphere are calledhydrometeors. These include rain,fog, hail, mist, snow, and frost.

Very small hail (0.2inch [5 mm] or lessin diameter) iscalled snow pellets.

6 7

that fell on April 14, 1986, inGopalganj, Bangladesh.

The heaviesthailstones

2 pounds(1 kg)

SNOWTiny ice crystals combine toform a hexagonal star, orsnowflake. They form at-4° F (-20° C).

42 METEOROLOGICAL PHENOMENA WEATHER AND CLIMATE 43

Normal visibility

6 miles(10 km)

ADVECTION FOGFormed when a mass of humidand cool air moves over a surfacethat is colder than the air

RADIATION FOGThis fog appears only on the groundand is caused by radiation coolingof the Earth's surface.

FRONTAL FOGFormed ahead of awarm front

The air becomessaturated as itascends.

The densest fog affects visibilityat this distance and hasrepercussions on car, boat, andairplane traffic. In many cases,visibility can be zero.

160 feet(50 m)

ASCENDINGAIR

F O G

B L O C K E D

F O G

F O G

F O G

1.

2.

4.

3.

MistMist consists of salt and other dryparticles imperceptible to thenaked eye. When the concentrationof these particles is very high, theclarity, color, texture, and form ofobjects we see are diminished.

660 feet(200 m)

0.6 mile(1 km)

1.2 miles(2 km)

1.9 miles(3 km)

160 feet (50 m)

DENSEFOG

Means of transport are affected by visibility.

THICKFOG

FOG MIST

When atmospheric water vapor condenses near the ground, it forms fog and mist. Thefog consists of small droplets of water mixed with smoke and dust particles. Physicallythe fog is a cloud, but the difference between the two lies in their formation. A cloud

develops when the air rises and cools, whereas fog forms when the air is in contact with theground, which cools it and condenses the water vapor. The atmospheric phenomenon offog decreases visibility to distances of less than 1 mile (1.6 km) and can affectground, maritime, and air traffic. When the fog is light, it is called mist.In this case, visibility is reduced to 2 miles (3.2 km).


Orographic barrierFog develops on lee-side mountainslopes at high altitudes and occurswhen the air becomes saturatedwith moisture.

OROGRAPHICFOG

DewThe condensation of watervapor on objects that haveradiated enough heat todecrease their temperaturebelow the dew point

Wind

Warm air

Highlandmasses

Types of FogRadiation fog forms during cold nightswhen the land loses the heat that was

absorbed during the day. Frontal fog forms whenwater that is falling has a higher temperaturethan the surrounding air; the drops of rain

evaporate, and the air tends to become saturated.These fogs are thick and persistent. Advectionfog occurs when humid, warm air flows over asurface so cold that it causes the water vaporfrom the air to condense.

Fog and VisibilityVisibility is defined as a measure of an observer'sability to recognize objects at a distance through the

atmosphere. It is expressed in miles and indicates the visuallimit imposed by the presence of fog, mist, dust, smoke, orany type of artificial or natural precipitation in theatmosphere. The different degrees of fog density havevarious effects on maritime, land, and air traffic.

Lost in the Fog

INVERSION FOG When a current of warm, humid airflows over the cold water of an ocean orlake, an inversion fog can form. Thewarm air is cooled by the water, and itsmoisture condenses into droplets. Thewarm air traps the cooled air below it,near the surface. High coastallandmasses prevent this type of fogfrom penetrating very far inland.


Brief Flash


Electrical storms are produced in large cumulonimbus-type clouds, which typicallybring heavy rains in addition to lightning and thunder. The storms form in areasof low pressure, where the air is warm and less dense than the surrounding

atmosphere. Inside the cloud, an enormous electrical charge accumulates, which isthen discharged with a zigzag flash between the cloud and the ground, between thecloud and the air, or between one cloud and another. This is how the flash of lightningis unleashed. Moreover, the heat that is released during the discharge generates anexpansion and contraction of the air that is called thunder.

ELECTRICAL CHARGESThe cloud's negative charges are attractedto the positive charges of the ground. Thedifference in electrical potential betweenthe two regions produces the discharge.

INSIDE THE CLOUDElectrical charges are produced from thecollisions between ice or hail crystals.Warm air currents rise, causing thecharges in the cloud to shift.

ORIGIN

Lightning originates within largecumulonimbus storm clouds.Lightning bolts can have negative orpositive electric charges.

The electricitymoves from thecloud toward an airmass of oppositecharge.

A lightning flashcan occur within acloud or betweentwo oppositelycharged areas.

Negative chargesof the cloud areattracted by thepositive charges ofthe ground.

8,700 milesper second(140,000 km/s) speed

100 million voltsIS THE ELECTRICAL POTENTIAL OF A LIGHTNING BOLT.

DISCHARGEThe discharge takes place from the cloudtoward the ground after the steppedleader, a channel of ionized air, extendsdown to the ground.

Lightning bolt: 8,700 miles per second (140,000 km/s)

Airplane: 0.2 mile per second (0.3 km/s)

F1 car: 0.06 mile per second (0.1 km/s)

A windmillgenerates 200volts.

110 volts isconsumed bya lamp.

Lightning can be distinguished primarily bythe path taken by the electrical charges thatcause them.

TYPES OF LIGHTNING

Cloud-to-groundCloud-to-cloudCloud-to-air

DISCHARGE SEQUENCE

INDUCED CHARGE

The negative charge of the base ofthe cloud induces a positive charge inthe ground below it.

The lightning boltpropagates through anionized channel thatbranches out to reachthe ground. Electricalcharges run along thesame channel in theopposite direction.

If the cloud has additionalelectrical charges, theyare propagated to theground through thechannel of the first stroke and generate asecond return stroketoward the cloud.

This discharge, as inthe second stroke,does not havebranches. When thereturn dischargeceases, the lightningflash sequence comesto an end.

The primary function of lightning rods is to facilitatethe electrostatic discharge, which follows the pathof least electrical resistance.

LIGHTNING RODS

1. 2. 4.

THUNDERThis is the soundproduced by the air whenit expands very rapidly,generating shock wavesas it is heated.

RETURN STROKE In the final phase, the dischargerises from the Earth to the cloud.5.

3.

A B CPOINT OF IMPACT

65 feet (20 m)This is the radius of a lightning bolt's effective

range on the surface of the Earth.

A lightning rod is an instrument whose purpose is to attract alightning bolt and channel the electrical discharge to the ground so

that it does no harm to buildings or people. A famous experiment byBenjamin Franklin led to the invention of this apparatus. During alightning storm, he flew a kite into clouds, and it received a strongdischarge. That marked the birth of the lightning rod, which consists ofan iron rod placed on the highest point of the object to be protected andconnected to the ground by a metallic, insulated conductor. The principleof all lightning rods, which terminate in one or more points, is to attractand conduct the lightning bolt to the ground.

1st phase

1st return

2nd phase

2nd return 3rd return

3rd phase

Cold air Warm air

SEPARATIONThe charges become separated, with thepositive charges accumulating at the top of thecloud and the negative charges at the base.

Cold airVery hot

air Cold airVery hotair

Tip of theconductor

Lightningrod

channel

For E

valuation Only.

Copyright (c) by F

oxit Softw

are Com

pany, 2004E

dited by Foxit P

DF

Editor

Flooded LandWhen land is flooded for days ormonths, the air in the soil is replaced

by water, which prevents the buildup ofoxygen, thus affecting the biological activityof plants and the soil itself. In the lattercase, if the water does not have sufficientsalt, the incomplete decomposition of organicmatter and the significant washing away ofnutrients make the soil more acidic. If thewater contains a great deal of salt, the saltwill remain in the soil, causing a differentproblem: salinization.

Torrential rains raise the level ofthe water in therivers and theriverbeds.

Little or no rainpenetrates into thevalley slopescovered with pines.

Low-lying terrain The main river cannotcontain the increasedflow of the tributaryrivers.

Principalriver

Tributaryriver

Houses andtrees coveredwith water

Electricalenergy can bemade availableto houses.

Agriculture ismore productivewhen water canbe controlled.

Large rivers cross theplains, which sufferfrom regular flooding

Snowincreases runoffinto the rivers.

Naturalcourse ofthe river

Hydroelectricdam

Channeling watervia turbines alsogenerateselectricity.

Damstores water todivert it or toregulate its flowoutside the riverbed.

Filtering gratesprevent the passage ofunwanted objects in thewater used to producehydroelectric power.

Transformers Their job is totransform the voltageof the electric current.

Electrical generatorEquipment thatproduces electricity byconverting themechanical energy ofthe rotating turbineinto electrical energy

Elevationof thereservoir

The components of the soil thatare oxidized can be reduced andthus change their properties.

ReductionSolid particulates

The water causes a declinein oxygen in theaerated spaces ofthe soil.

The soil cannotcarry oxygen tothe roots.

Electricalpower lines

When Water AccumulatesW

ater is a vital element for life, but in excess it leads to serious consequences for peopleand their economic activity. Flooding occurs when certain areas that are normally dryare covered with water for a more or less prolonged period. The most important causes

are excessive rains, the overflow of rivers and lakes, and giant waves that wash over the coast.Such waves can be the result of unusually high tides caused by strong surface winds or bysubmarine earthquakes. Walls, dikes, dams, and embankments are used to help prevent flooding.

FloodplainsFloodplains are areas adjacentto rivers or streams that aresubject to recurrent flooding.

EMBANKMENTEarthen embankments helpcontain rivers that tend tooverflow and temporarilychange course.

STORM DIKESIn areas where the coast is low and exposed to flooding,protective dikes have been constructedagainst high tides and powerful waves.


TorrentialRainsCaused by low pressuresystems, instability ofthe air mass, and highhumidity

Victims of flooding in the Bayof Bengal, Bangladesh, in 1970

250,000

Flood ControlWith the construction of dikes andembankments, the flow of rivers proneto flooding is largely contained.

HydroelectricPlantsuse the force and velocity of runningwater to turn turbines. There are twotypes: run-off-river (which uses thenatural kinetic energy of the river'srunning waters) and reservoir (where thewater accumulates behind dams and isthen released under increased pressure tothe power plant).

Plants with thick,droopy stems

There is so muchwater on thesurface that the soilcannot absorb it.

FIELD CAPACITYThe amount of moisture inthe soil remaining afterwater has run off thesurface. Field capacitydetermines whether, evenwith a meteorologicaldrought, the land cancontinue to absorbexisting water betweensoil particles.

In deserts, drought from lack of rain is customary,but in arid, semiarid, and subhumid regions,desertification occurs when for weeks, months, or

years the land is degraded because of climatic variations. A high-pressure center that stays in a certain location longer thanusual can be the cause of this phenomenon. Soils are able to put upwith a certain dry period, but when the water table decreasesdrastically, the drought can turn into a natural catastrophe.

Water Scarcity


Air

Hygroscopicwater

Solidparticles

Solidparticles

SATURATED SOILThe water that falls asprecipitation may bemore than the soil canabsorb, and it descends

toward aquifers.

WILTINGThis results when lesswater is available in theupper layers of the soil.

AGRICULTURAL DROUGHTWhen soil moisture exists only at the hygroscopiclevel (surface moisture on soil particles), there isno water available for vegetation.

Remainingwater

Solidparticulates

Gravitationalwater

Capillarywater(osmosis)

Capillarywater

Solidparticles


CY

CL

ON

I CC

UR

RE

NT

METEOROLOGICAL DROUGHTThe condition that results whenprecipitation is much lower than normallevels for that location. It is generallydetermined based on comparison withaverage rainfall.

THE PROPORTIONOF WATER IN THESOIL

Excesswater(saturation)

Saturationthreshold(fieldcapacity)

Level ofwilting

Hygroscopiccoefficient(minimum ofwater)

Solidparticles

Spacebetweenthe pores1933-37

The Dust Bowl was created.1962-66Affected the statesof the Northeast1977Water is rationed inCalifornia.

UNITEDSTATES

1975-76Less than 50% ofthe average rainfall

ENGLAND

SAHEL

1965-671.5 million deathscaused bydrought

1967-69Numerousforest fires

AUSTRALIA

INDIA

THE DRIEST ZONEScoincide with deserts. For example, in theAtacama Desert in northern Chile, not a singledrop of water fell between 1903 and 1917.

The region of the Sahel hasendured periods of devastatingdroughts lasting this long.

100 years

1

2

3 4

5Areas of insufficient rainfor normal vegetationand harvests

KEY

H I G H - P R E S S U R EA

R

EA

B HIGH PRESSUREA high-pressure center, or anticyclone, is morestationary than usual and

creates an abnormal situation in the region.

C DROUGHTThe jet-stream currents are thrown off course by the high-pressure center, whichimpedes rainfall. A dryperiod begins.

A RAINCaused by cyclonic(low pressure) aircurrents.

The length of the path along the groundover which a tornado can move

125 miles(200 km)

Maximum height that it can attain

6 miles(10 km)

FUJITA SCALEThe Fujita-Pearson scale wascreated by Theodore Fujitato classify tornadoesaccording to the damagecaused by the wind, from thelightest to the most severe.

F2 F4 F5F3

Damage tochimneys, tree

branches broken

Houses uprooted fromtheir foundations and

dragged great distances

Solidly builtwalls blown

down

Roofs and wallsdemolished, cars and

trains overturned

Mobile homesdestroyed, trees

felled

Mobile homesripped from their

foundations

F1F0

WIND VELOCITY MILESPER HOUR (KM/H)

40-72(64-116)

73-112(117-180)

113-157(181-253)

158-206(254-332)

207-260(333-418)

261-320(420-512)

CATEGORY

EFFECTS

TOPThe top of the

tornado remainsinside the cloud.

PATHNormally the tornado pathis no more than 160 to330 feet (50-100 m) wide.

VORTEXColumn of air that formsthe lower part of atornado; a funnel thatgenerates violent windsand draws in air. Itusually acquires the darkcolor of the dust it sucksup from the ground, butit can be invisible.

MULTIPLEVORTICESSome tornadoeshave a numberof vortices.

SPIRALING WINDSFirst a cloud funnelappears that can thenextend to touch theground.

Some tornadoes areso powerful thatthey can rip theroofs off houses.

The tornadogenerally movesfrom thesouthwest to thenortheast.

ROTATIONThe circulation of the aircauses a decrease inpressure at the center ofthe storm, creating acentral column of air.

2.

DESCENTThe central whirling columncontinues to descend withinthe cloud, perforating it inthe direction of the ground.

3.

THE OUTCOMEThe tornado reaches theEarth and depending on itsintensity can send the roofsof buildings flying.

4.

BEGINNING OF A TORNADOWhen the winds meet, theycause the air to rotate in aclockwise direction in theSouthern Hemisphere and inthe reverse direction in theNorthern Hemisphere.

1.

How They Form

Where and When Most tornadoes occur in agricultural areas. Thehumidity and heat of the spring and summer are

required to feed the storms that produce them. In order togrow, crops require both the humidity and temperaturevariations associated with the seasons.

Tornadoes

Agricultural areas

Convection

Spinningfunnel of air

Strong wind

MildWind

Cold anddry wind

Warm andhumid wind

Humidwind

Storm

Cumulonimbus

Maximum velocity the tornadowinds can attain

300 milesper hour(480 km/h)

tornadoes are generatedon average annually inthe United States.

1,000The period of the day withthe highest probability oftornado formation

3:00 P.M.-9:00 P.M.

0.6 mile (1 km)Maximumdiameter

Tornadoes begin to form when a current of warmair ascends inside a cumulonimbus cloud and

begins to rotate under the influence of winds in theupper part of the cloud. From the base of the column, airis sucked toward the inside of the turning spiral. The air

rotates faster as it approaches the center of the column.This increases the force of the ascending current, andthe column continues to grow until it stretches from highin the clouds to the ground. Because of their shortduration, they are difficult to study and predict.


Lethal ForceT

ornadoes are the most violent storms of nature. They aregenerated by electrical storms (or sometimes as the result of ahurricane), and they take the form of powerful funnel-shaped

whirlwinds that extend from the sky to the ground. In these storms,moving air is mixed with soil and other matter rotating at velocities ashigh as 300 miles per hour (480 km/h). They can uproot trees, destroybuildings, and turn harmless objects into deadly airborne projectiles. Atornado can devastate a whole neighborhood within seconds.

Death and DestructionO

f the 1,000 tornadoes that annually strike the United States, there is one that has the unfortunatedistinction of being one of the worst: the Tri-State tornado, which occurred on March 18, 1925, andcaused extreme devastation. It moved across Missouri, Illinois, and Indiana, destroying homes and

causing the confirmed deaths of 695 people, although it is believed that the number may have been muchhigher. The tornado traveled 230 miles (368 km) at an average velocity of 66 miles an hour (105 km/h),and its duration set a record at three hours and 30 minutes. It has been rated on the Fujita scale as anF5 tornado—one of the most damaging—and caused losses to the United States of $17 million.


MISSOURI(U.S.)Latitude 37° N

Longitude 93° W

F5

3 hours 30 minutes

66 miles per hour (105 km/h)

1:01 P.M.First contact with the ground

4:30 P.M.Final contact with the ground

THE 10 MOST DEVASTATING TORNADOES

Deaths

Injuries

ELLINGTONFirst townaffectedOne dead

ANNAPOLISAND LEADANNALarge number of victims75 injured and 2 dead

PRINCETONHalf of the towndestroyed 65 deaths

REDFORDTown hit bytornado

Value on the Fujita scale

Duration

Average velocity

OWENSVILLESerious damage to houses

BIEHLEA number ofhouses destroyed

WEST FRANKFORTPartial destruction450 wounded and 127 dead

dollars in losses

17 million

houses destroyed

15,000

GORHAMTown in ruins34 dead

PARRISHAlmost totaldestruction22 dead

MURPHYSBOROTown with thegreatest number offatalities234 dead

100percent destroyed

90percent destroyed

90percent destroyed

40percent destroyed

20 percent destroyed

50percent destroyed

I L L I N O I S

I N D I A N A

Tornadoes in the United StatesUnlike hurricanes, which are tropical storms primarily affecting theGulf of Mexico, tornadoes are phenomena that occur between the

Great Plains of the United States, the Rocky Mountains, and the Gulf ofMexico and usually appear in the spring and summer.

The period of the daywith the highestprobability of tornadoformation

3:00 P.M.-9:00 P.M.

The number oftornadoes occurringper year in theUnited States

1,000

R u r a l a r e a

GRIFFIN150 housesdestroyed, andmany childrenkilled.100

percent destroyed

66 miles per hour

(107 km/h)

60 miles per hour

(96 km/h)

60 miles per hour

(96 km/h)

M I S S O U R I

DE SOTOPartialdestruction buta large numberof victims69 dead

30percent destroyed

In 40 minutes,541 people died.

THE TOWN OFGRIFFIN, INTHE STATE OFINDIANA, WASLEFT IN RUINS.

71 miles per hour

(115 km/h)

71 mile

s per h

our

(115 km/h

)

55 miles per hour

(90 km/h)


WEATHER AND CLIMATE 5756 METEOROLOGICAL PHENOMENA

Ahurricane, with its ferocious winds, banks of clouds, and torrentialrains, is the most spectacular meteorological phenomenon of theEarth's weather. It is characterized by an intense low-pressure

center surrounded by cloud bands arranged in spiral form; these rotatearound the eye of the hurricane in a clockwise direction in the SouthernHemisphere and in the opposite direction in the Northern Hemisphere.While tornadoes are brief and relatively limited, hurricanes are enormousand slow-moving, and their passage usually takes many lives.

DEVELOPMENT

Begins to ascend,twisting in a spiral arounda low-pressure zone

BIRTH

Forms over warm seas, aidedby winds in opposing directions,high temperatures, humidity,and the rotation of the Earth

1.2.

Anatomy of a Hurricane

DEATH

As they pass from the sea tothe land, they cause enormousdamage. Hurricanes graduallydissipate over land from thelack of water vapor.

3.The high-altitudewinds blow fromoutside the storm.

THE EYECentral area,has very lowpressure

Hurricanes in theNorthern Hemisphererotate counterclockwise,and those in theSouthern Hemisphererotate clockwise.

VAPORRises warm from the sea,forming a column ofclouds. It rises 3,900 feet(1,200 m) in the center ofthe storm.

19 miles per hour(30 km/h)VELOCITY AT WHICH ITAPPROACHES THE COAST

80º F(27º C)

is the minimum temperaturethat water on the surface ofthe ocean will evaporate at.

Strong ascendantcurrents

Cloud bands inthe form of a

spiral

FRINGES OF STORMCLOUDSotate violently aroundthe central zone.

DANGER ZONE

The areas that are vulnerable to hurricanes in theUnited States include the Atlantic coast and the coastalong the Gulf of Mexico, from Texas to Maine. TheCaribbean and the tropical areas of the westernPacific, including Hawaii, Guam, American Samoa, andSaipan, are also zones frequented by hurricanes.

FRICTIONWhen the hurricane reachesthe mainland, it moves moreslowly; it is very destructive inthis stage, since it is here thatpopulated cities are located.

EYE WALLThe strongestwinds are formed.

The airwrapsaroundthe eye.

Descendingair currents

5

4

3

2

1

CLASSIFICATION OF DAMAGE DONE

minimum

moderate

extensive

extreme

catastrophic

CLASS 1

CLASS 2

CLASS 3

CLASS 4

CLASS 5

74 to 95 (119 to 153)

96 to 110 (154 to 177)

111 to 130 (178 to 209)

131 to 155 (210 to 250)

more than 155 (250)

4 to 5 (1.2 to 1.5)

6 to 8 (1.8 to 2.4)

9 to 12 (2.7 to 3.6)

13 to 18 (3.9 to 5.4)

more than 18 (5.4)

Saffir-Simpson category

Damage Speed milesper hour (km/h)

High Tidefeet (m)

MAXIMUM HEIGHTREACHED BY THE WAVES

(28 m)92 feet/high

PATH OF THEHURRICANE

The hurricanebegins to breakapart when itmakes landfall.

DAY 12Now mature, itdisplays a visible eye.

DAY 6

The spiralform becomesmore defined.

DAY 3

The cloudsbegin to rotate.

DAY 2A jumbleof cloudsis formed.

DAY 1

NH

SHSH

The trade windsare pulled towardthe storm.

Thewinds flowoutward.

Light winds giveit direction andpermit it to grow.

WIND ACTIVITY

CYCLONE

HURRICANETYPHOON

Equator


What Katrina Took Away

Hurricane Katrina lashed the south and the center of the United Statesin August 2005. The force of the wind razed thousands of houses,buildings, oil installations, highways, and bridges, leaving a vast area

of the country without communication and some heavily populated areaswithout provisions. It resulted in extensive material damage and thousandsof deaths in Florida, the Bahamas, Louisiana, and Mississippi. Satellite imagesreveal the scope of the disaster, considered one of the most devastating inthe history of the country.

The hurricane winds pushed thewater 14 feet (4.3 m) above thenormal sea level.

Along with the storm, thebacked-up water reaches thedikes of the Mississippi River.

ORLEANSAVENUE CANAL

17TH STREETCANAL

OVER

OVER

Area most affectedby the flood

Areas most affectedby the flood

Area of New Orleansaffected by flooding

80%

LAKE PONTCHARTRAIN

THE WATERadvances toward the city,invading the central regions.

6:00 A.M. The time whenthe hurricanemade landfall

NEW ORLEANSLatitude 30° N

Longitude 90° W

Area

Number of inhabitants

Altitude (above sea level)

360 square miles (933 square kilometers)

500,000

10 feet (3 m)

THE WINDSAt 155 miles per hour (250km/h), they force the wateragainst the protective walls..

DIKESwere breached by thewater and the wind,causing a great flood.

Deaths confirmed after Katrina

1,500

dollars was the cost of the repairs.

75 billion

AUGUST 23A tropical depression forms in theBahamas. It intensifies and becomestropical storm Katrina. On August25, it makes landfall in Florida as acategory 1 hurricane.

AUGUST 27Leaves the Gulf of Mexico andreaches category 3. On August 28,it is transformed from category 3to category 5 and increases in size.

CATEGORY 3

CATEGORY 4

CATEGORY 5

AUGUST 29In the early hours, it makes landfall inLouisiana as a category 4 hurricane.A little later, it makes landfall for thethird time, in Mississippi.

SEPTEMBER 1What remains of the hurricaneis weakened as it moves northto Canada, where it dissipates.

Direction ofthe hurricane

MAXIMUM WIND SPEED

155(250 km/h)

milesper hour

of the inhabitantsof this zone wereevacuated.

75%

Huracanes fueronregistrados en 2005.14El total de tormentastropicales registradas en el año 2005.

26


LONDONAVENUE CANAL

1BEFORE THE HURRICANEIf you live in a hurricane-pronearea, it is recommended that youknow the emergency plans of thecommunity and that you have aplan of action for your family.

DURING THE HURRICANEThe important thing is to remain calmand to stay informed via radio ortelevision about the path of the hurricane.Move away from doors and windows. Donot leave until the authorities announcethe danger from the hurricane has ended.

AFTER THE HURRICANEFirst verify that everyone in the family is welland that there are no injuries. Do not touchloose cables or fallen poles. Call the firedepartment or the police in case you needfood, clothing, or immediate medication.

HOW TO PREPAREEMERGENCY EQUIPMENTA complete first-aid kit must beprepared and available. Consult apharmacist or your family physician.

HOW TO PREPAREDOCUMENTATIONTo be prepared forevacuation, keep familydocuments in good order.

Foresight to Prevent Tragedies

First-aid courseYou should be preparedfor dealing with themost commonsymptoms and injuries.

InventoryMake a completelist of belongingsof each person.

Personal IDIt is importantfor everyone tohave an ID card.

Secure all thedoors andwindows to keepthem fromopening.

Storenonperishablefood andpotable water. Keep valuable

objects anddocuments ina waterproofcontainer.

Use a battery-powered radio totune into localstations to getinformation.

Do not touchwires or damagedelectricalequipment.

When you are onthe move, usecaution whetheron foot or driving.

Check the mostfire-prone areas.

Help peoplewho areinjured ortrapped.

Return homeonly when theauthorities saythat it is safe.

Keep documentsconfirming yourownership ofproperty close athand.

Do not drinkwater unlessyou are sure itis potable.

Use thetelephone onlyfor emergencycalls.

Verify that there areno natural-gas leaksor damage to theelectrical system.

Turn off the mainwater valve and

the main gas valve.

Follow news reports witha battery-powered radio.

Disconnect allelectricaldevices and shutoff the housecircuit breaker.

Administer first aidwhen necessary.

Keep thecar suppliedwith a fulltank of fueljust in case.

Reinforce roof tilesto keep them frombeing loosened.

60 METEOROLOGICAL PHENOMENA WWEATHER AND CLIMATE 61

First-aid kitCheck the first-aidkit and replace anyexpired items.

23

Hurricanes usually lash specific regions of the planet, and the population must becomeaware of the disasters that can strike the community. Each family must know whicharea of the house is the most secure in case the roof, a door, or a window collapses.

They must also know when it is time to go to a shelter or if it is better to remain at home.Another important precaution is to organize and store all family documents and real-estaterecords in a water- and fireproof strongbox.

Meteorology

The use of satellites orbiting theEarth, recording the coming ofrain, air currents, and clouds,allows us to know with somehours of advance warning if a

severe storm is heading toward a certainpoint on the planet. Counting on thistype of precise information about whenand where tropical cyclones will occur,for example, has allowed government

officials to coordinate the evacuation ofpeople from the affected zones. Thesurface of the planet is also monitoredby a system of meteorological stationsplaced hundreds of miles from each

other. These collect information from andsend information to all areas of the worldso that meteorologists can prepare maps,graphics, and predictions to inform thepublic.

WEATHER FOLKLORE 64-65

COMPILATION OF INFORMATION 66-67

INSTANTANEOUS MAPS 68-69

RAIN, COLD, OR HEAT 70-71

MOBILE SATELLITES 72-73

RITA, SEPTEMBER 2003The image from the GOES-12satellite shows the configurationof Hurricane Rita in the easternportion of the Gulf of Mexico.

Weather Folklore

Signs from Plants and AnimalsIn every rural community, concern for the harvest anddependency on weather resulted in a series of beliefs,

with varying degrees of accuracy, taken as prophesies oflater events. In any case, even though it is certain thatpeople as well as plants and animals react to the currentweather, there is nothing to indicate that this might revealanything about the weather in the future except to thedegree that an incipient change is related to the currentweather. For example, some signs accompany the increase inhumidity that occurs prior to the passage of a cold front.

64 METEOROLOGY

DRY SEAWEEDThe lower the humidity, themore probable it is that thenext day will be dry.


Moon

Almanac ForecastsIn the 16th century, almanacs with weather forecasts weresold throughout Europe. Each month of the year has its own

refrain, although this depends on the hemisphere a person lives in.The monthly and annual calendars offered agricultural and medicaladvice. From the most remote times, there was a general belief thatthe Moon determined the behavior of the atmosphere and thatvariations in the weather were caused by changes in the phase ofthe Moon. Some examples of these popular sayings are: “SweetApril showers do spring May flowers;” “After a dark winter's night,the next day will be bright.”

WINDWind from the east, rain like a beast.

CLEAR SUNSETRainbow at sundown, goodweather at dawn.

Clouds with a fringe or lining—secure your sails well.This relates to clouds that are carriedby winds at high altitudes; these cloudsare often a sign that a low-pressuresystem, or cyclone, is approaching.

Clouds

MORNING DEWDew and cool in May, bring wineto the vine and hay to the cow.

WEATHER PREDICTION There are thousands of refrains thatrefer to changes in weatherconditions. Here are some examples.

When you see a black slug inyour way, rain is not far away. Snails are usually hidden in thegarden. You see them only onhumid days, just prior to the rain.

Snails

ASHIf the leaves of the ash fallbefore those of the oak,the summer will be wet.

OAKIf the leaves of theoak fall before thoseof the ash, thesummer will be dry.

When you see a toad walking, itwill be a wet spring.When a toad is swimming in thewater, this means it will soon rain.If it stays in the water withoutmoving, the rain will lastfor some time.

Toad

When swallows fly low, getyour rain gear in tow. Swallows usually appear beforea heavy rain.

Swallow

OPEN AND CLOSEDPINECONESOpen pinecones mean dryweather; closed pineconesmean humid weather.

When the Moon has a halo,tomorrow will have wet or bad weather.Halos occur as a consequence of therefraction of light by ice crystals incirrostratus clouds covering the Sun or Moon.They portend a warm front, which will befollowed by rain.

I hear donkeys braying; I amsure it will rain today.The animals react to the existingweather. It is a sign associatedwith the increased humidityin the environment.

Donkey

Before the development of meteorology as we know it today,people observed in nature signs that allowed them topredict rains, floods, or strong winds. All this knowledge

has been transmitted over the centuries in the form of proverbsor rhymes. Most of these fragments of meteorological knowledgelack a scientific foundation, but some of them reflect certainprinciples. Plants and animals play a major role in theseobservations.

The intervals burned givea count of the hours ofsunlight during the day.

66 METEOROLOGY

Compilation of Information


ANEMOMETERmeasures the speedof the wind. Thisinstrument isactivated by thewind, which turnsthree hemisphericalcups mounted on avertical rod firmlyplaced in the ground.

Three equallyspaced cupsrecord theintensity ofthe wind.

WEATHER VANEshows which way thewind is blowing. It is aperfectly balancedmechanical system.

WorkplaceA typical meteorological station checks thetemperature, humidity, wind velocity and

direction, solar radiation, rain, and barometricpressure. In some places, soil temperature andflow of nearby rivers are also monitored. Thecompilation of this data makes it possible to

predict different meteorological phenomena.

HELIOPHANOGRAPHAn instrument used tomeasure the numberof hours of sunlight. Itconsists of a glasssphere that acts as alens to concentratesunlight. The light isprojected onto a pieceof cardboard behindthe sphere. Thecardboard is burnedaccording to theintensity of the light.

The light strikes andis concentrated as ittraverses the sphere.

Automatic Weather Station An automatic meteorological station uses electricalsensors to record temperature, humidity, wind velocity

and direction, atmospheric pressure, and rainfall, amongother parameters. The readings are processed bymicroprocessors and transmitted via an automatic system.This station functions autonomously, 24 hours a day,powered by solar energy (solar panels) or wind energy.

Wet-bulbthermometer

Dry-bulbthermometer

PSYCHROMETERmeasures therelative humidity ofthe air. It consists oftwo thermometersand two bulbs (onedry and one coveredwith muslin that isalways kept damp).

Container ofdistilled water

MINIMUMTHERMOMETERindicates the lowesttemperature of the day. Ithas a fork-shaped bulb.

Bulb withalcohol

RAIN GAUGEThe precipitation that falls onthe ground in the form of rain iscollected by the rain gauge.

RAIN METERThis is used to keepa chronologicalrecord of theamount of waterfalling as rain.

EVAPORIMETERAs its name indicates,it measures theeffective evaporationof water from a massof liquid in the openair, from its loss fromthe surface throughtransformation towater vapor.

Thermometer

Woodenplatform

METEOROLOGICAL SHELTERIt is built of wood or fiberglass on a base that insulates it fromthe soil and protects certain instruments (thermometers,psychrometers, and others) from solar radiation. Screens in thewindows ensure good ventilation.

Mouth

SiphonCollectorcontainer

Recordingpen

Drum

Slats allow the airto flow throughfreely withoutcreating currents.

Double circulation of the air to prevent theheating of the instruments when the radiationis very intense

Scale

Levers

Spiralspring

Metaldrum

Chains

Spring

ANEROID BAROMETERmeasures atmosphericpressure. Changes areshown by the pointers.

760 mm

IMPRESSION The concentrated rays of sunlight burncardboard placed behind the glass sphere.

MAXIMUM THERMOMETERshows the highest temperature of the day. Thecapillary with mercury is calibrated in the bulb.

Weather Station Meteorologists collect data atdifferent heights. They use various

instruments at ground level: athermometer for temperature, ahygrometer for humidity, and a barometerfor atmospheric pressure.

HYGROTHERMOGRAPHsimultaneously records theair temperature andrelative humidity. Athermograph and ahygrograph independentlymake records on paper ofthe daily variations intemperature and humidity.

Psychrometer

Maximum andminimumthermometers

Hygrothermograph

Most of the information available regarding climaticdata comes from the record thatmeteorologists everywhere in the world

keep regarding cloud cover, temperature, theforce and direction of the wind, air pressure,visibility, and precipitation. Then from eachmeteorological station, the data is sent byradio or satellite, and this makes it possible tomake forecasts and maps.

MERCURY BAROMETERAn instrument used to measureatmospheric pressure. It consistsof a glass tube full of mercury,with the open end submerged ina reservoir.

BAROGRAPHmeasures theatmospheric pressureand records itschanges over time.

Mercury

Atmosphericpressure

Record on a stripof cardboardgraduated in hours

Vacuum

Radar

DATARECORDERrecords thedata obtained.

In the NorthernHemisphere, thedoors should beoriented towardthe north toprevent the Sun'srays from strikingthe instrumentswhen observationsare being made.

Bulb withmercury

2 °

Indicatesthe directionof the wind

Weathervane

Anemometer

Solar panelData recorder

Controlunit

Rain Meter

Weather maps represent at any given moment the state of the atmosphere at differentaltitudes. These maps are made based on the information provided by meteorologicalstations and are useful for specialists. The data collected by them include various values

for pressure and temperature that make it possible to forecast the probability of precipitation,whether the weather will remain stable, or if it will change because a weather front is moving in.

Instantaneous Maps

ANTICYCLONE

In this area, theatmospheric stability is high,since the downward motionof the air prevents theformation of clouds. There islow probability of rain.

SYMBOLS

There are a number of differentsymbols to represent differentkinds of fronts.

WINDS

The direction and intensity of thewinds are indicated by a segmentwith a circle at its end, whichindicates the direction from which thewind is blowing. On this segment,perpendicular lines are traced thatindicate the velocity of the wind inknots, where one knot equals 1.2 milesper hour (1.9 km/h).

NOMENCLATURE

Every meteorologicalmap carries a label thatindicates the date andtime it was made.

68 METEOROLOGY

LOW PRESSURE,OR DEPRESSION

In this zone, atmosphericstability will be low giventhat the air is rising, andthere is a high probabilityof precipitation.

HIGH PRESSURE This is a high-pressure area. Thepressure decreasesfrom the internalisobars toward theexternal isobars.

LOW PRESSUREThis is a low-pressure zone. Thepressure increasesfrom the internalisobars toward theexternal isobars.

WINDSThey circulateand move awayfrom the area. WINDS

circulate around thecenter of the area.

Isobar MapsOne of the variables that provides the most informationin real time for knowing meteorological conditions is

atmospheric pressure, whose values over land (at sea level)are represented on what are called isobar maps, or ground-level weather maps. The isobars, or lines that connect pointsof equal pressure, make it possible to estimate the velocityand direction of the wind at ground level. This informationhelps forecast the movement of cold or warm air masses. Theletter A indicates an anticyclonic area, which indicatesatmospheric stability and that the probability of rain is verylow. The letter B indicates a low-pressure area and presagesmajor atmospheric instability with possible rain.

WARM A warm air mass withlocal storms is advancing.

COLD A cold air mass with rain isadvancing.

Upper-air MapAnother type of map, which is used toanalyze upper-air weather conditions, is an

upper-level, or geopotential, map. On these maps,contour lines connect points located at the samealtitude for a certain pressure level (normally500 hectopascals [hPa]) and correlate with thetemperature of the air in the higher layers of thetroposphere (at 16,400 feet [5,000 meters]altitude on the 500 hPa map). The temperatureis represented in each region of the troposphereby lines called isotherms.

OCCLUDED FRONTindicates the line ofcollision between a coldfront and a warm front.These are usuallyassociated with severestorms.

INIT

: TU

E, 0

2SEP

200

3 12

Z

This map is preparedwith the initialvalues of Tuesday,September 2.

12 indicates the hourand Z GreenwichMean Time.

It indicates theinitial values.

OCCLUDED FRONTIt is mixed; it will act first as a warmfront and then as a cold front.

STATIONARY Moderately bad weatherand little change of temperature

ISOBARSare lines joining pointsof equal pressure.

LOW-PRESSURETROUGH AXIS

HIGH-PRESSURERIDGE AXIS

BAD WEATHERInstability andhigh probabilityof abundantrain

GOOD WEATHERAtmosphericstability and lowexpectation ofprecipitation

SYMBOLSThe direction ofthe wind isrepresented bythese symbols:

WIND VELOCITYA short lineindicates fiveknots, a longer lineindicates 10 knots,and a terminaltriangle indicatesmore than 40knots.

POSITIONThe line indicatesthe direction of thewind. It can benorth, northeast,east, southeast,south, southwest,west, or northwest.

OVERCAST SKYA black circleindicates anovercast sky anda white circle aclear sky.

500 HPAThe first pressure value thatrepresents a geopotential of500 hectopascals (hPa)

UPPER-LEVEL MAPS

The contour lines traced inthese charts connect pointsof equal geopotential height,which define high-pressureridges and low-pressuretroughs. The wind direction isparallel to these lines. Thesecharts are used to prepareweather forecasts.

36,100 FEET (11,000 METERS)

18,000 FEET (5,500 METERS)

9,800 FEET (3,000 METERS)

4,900 FEET (1,500 METERS)

0 FEET (0 METERS)

250 hPa

500 hPa

700 hPa

850 hPa

SURFACE

1686is the year in which Englishastronomer Edmond Halleymade the firstmeteorological map.

HIGH-PRESSURERIDGE

Area of high geopotentialvalues in which the chancesof rain are slight


1030

990

995

1000

1025

1020

1015

LOW-PRESSURE TROUGH

This phenomenon increases theprobability of bad weather. Alow-pressure trough has a lowgeopotential value.

JETG-IV

HURRICANE HUNTER P-3AIRPLANEIts Doppler radar has a resolution fourtimes greater than the standardDoppler radar in conventional use.

METEOROLOGICAL AIRCRAFTobtain temperature and humidity dataand photograph particles contained inthe clouds.

LAUNCHABLE SOUNDING PROBEis launched from an airplane toward theground. Its trajectory is followed as itrelays information about wind velocity,temperature, humidity, and pressure.

RADAR STATIONis utilized to measure the intensity withwhich rain, snow, or ice is falling. Theradar sends radio waves that bounce offraindrops, and the return signal isdisplayed on a receiving screen.

METEOROLOGICAL STATIONMeasurements at ground level permitthe collection of partial data.Thermometers measure temperature,the hygrometer measures humidity, andthe barometer measures atmosphericpressure.

RADIOSONDEcarries out airborne measurements oftemperature, pressure, and relativehumidity at different altitudes oratmospheric levels. It also indicatesthe direction and speed of the wind.

AEROSONDEPilotless weather aircraftcapable of sendingmeteorologicalinformation at intervals oftenths of a second

ARTIFICIAL SATELLITESprovide images used for visualizingclouds and water vapor in theatmosphere and for measuring thetemperature of land and oceansurfaces.

ACOUSTIC SIGNALAn acoustic depthsounder sends outsound waves tomeasure the depthof the water.

NavigationlightsAnemometerDatatransmitterSolar panel

is the depth reachedby the vehicle.

6,600 feet(2,000 m)

is the altitude that aradiosonde can reach.

49,200 feet(15,000 m)

is the altitude that can bereached by the G-IV airplane.

49,200 feet(13,000 m)

is the altitude that can be reachedby a radio sounding probe.

1,200 feet(365 m)

32,800 feet(10,000 m)

Parachuteslengthen thetime in theair.

Radiosondesends information tothe base.

DATA COLLECTIONThe World MeteorologicalOrganization acts as a center forreceiving and transmitting datacoming from various stationslocated in the air, on the ocean,and on land.

Knowing ahead of time what the weather will be is sometimes a question of life or death.The damage resulting from a torrential rain or a heavy snowfall can be avoided thanks tothe forecasts of meteorologists. The forecasts they make are based on information

gathered from many sources, including instruments on the ground, in the air, and at sea. Despitethe use of sophisticated information systems, the weather can be forecast only for the next fewhours or days. Nonetheless, it is very useful in helping to prevent major catastrophes.

Rain, Cold, or Heat

METEOROLOGICALBUOYprovides informationabout conditions of thesea in areas that arenot covered by ships.The buoy floats freelywith the ocean currentsand transmits readingsautomatically viasatellite.

MARITIMESOUNDINGPROBESThey are droppedfrom airplanes andthen sink.

70 METEOROLOGY

On the SeaBoats, buoys, and autonomous underwater vehicles help measurewater temperature, salinity, density, and reflected sunlight. All

the information gathered is sent to a meteorological center.

In the AirData can be collected byairplanes, satellites, or

sounding probes. One singlesatellite can cover the entiresurface of the Earth. Preciseinformation helps preventmeteorological catastrophessuch as hurricanes or flooding.

On LandThe observations made at groundlevel are more numerous than those

made at higher altitudes. They includemeasurements of atmospheric pressure,temperature, humidity, wind direction andvelocity, the extent and altitude of cloudcover, visibility, and precipitation.

OCEANOGRAPHIC SHIPgathers data on the direction andspeed of the wind and thetemperature of the air and water,among other things.

METEOROLOGICAL CENTERSThey improve worldwide cooperation inmeteorological observations, normalize thedata obtained in different cities throughoutthe world, and promote the application offorecasts to various human activities.

AUTONOMOUS UNDERWATER VEHICLE Images related to the physical properties of theocean water, such as the temperature, salinity, anddensity, are relayed to operators and its location anddepth tracked via the Global Positioning System (GPS).

Satellite

Radiosonde

Boat

Launchablesounding probe

Marinesoundingprobe

Buoy

Airplane

Radar

Station

Meteorological center

CURRENTMODEL

EXPERIMENTALMODEL

Scale of 7 miles(12 km) per side

Scale of 1 mile(1.3 km) per side

The height at whichthey fly, near theupper limit of thetroposphere

is the altitude that can bereached by the P-3 aircraft.

14,000 feet(4,270 m)

Dopplerradar

Better ForecastsNew models that measure changes in suchvariables as humidity, temperature, wind

velocity, and cloud displacement may make itpossible to improve forecasts by 25 percent overcurrent ones.

Strongest winds.They are not detectedby current models.

WWEATHER AND CLIMATE 7372 METEOROLOGY

Mobile SatellitesM

eteorological satellites, which have been orbiting the Earth for more than 30 years,are an indispensable aid to scientists. Along with the images generated by theseinstruments, meteorologists receive data that can be used to prepare weather

bulletins. These reports, circulated via the mass media, allow people all over the worldto know the weather forecast. Moreover, the most advanced satellites are used tostudy the characteristics of phenomena such as tropical cyclones (hurricanes,cyclones, and typhoons).

POLAR ORBIT28,400 miles(45,700 km)

TWO ORBITSPER DAY190 miles persecond (305km/sec)is the velocity of apolar satellite atan altitude of 560miles (900 km).

EQUATOR EQUATOR

Transmittingantenna

Receivingantenna

X-raysensors

Telemetryantenna

Log periodicantenna

Imagereception

Magnetometer

UHF antenna

Solarpanels

Arraydrive

NOAA-12 NOAA-14

NOAA-15 METEOR 3-5

GOES 8 GOES 9

METEOSAT-7 GMS

Images, Yesterdayand Today

The TIROS satellites (Television andInfra-Red Observation Satellite) of

the 1960s provided the first images ofcloud systems. The modern GOESsatellites (Geostationary OperationalEnvironmental Satellites), which takemore precise time and spacemeasurements, provide higher-qualityimages of clouds, continents, andoceans. They also measure the humidityof the atmosphere and the temperatureat ground level.

represents infrared emissions or heat fromthe clouds and from the Earth's surface.Objects that are hotter appear darker.

INFRARED IMAGE

They are composed of infraredimages (which permitdifferentiation of high and lowclouds) and visible-light images(which measure the reflectivity ofeach climatic subsystem).

COMBINED IMAGES

Oceans and continents have lowalbedo and appear as darkerareas. Areas with high albedo, incontrast, are clear and bright.

VISIBLE IMAGE

GeostationaryThey orbit the Earth above the Equatorand are synchronized with the Earth'srotation—that is, as they orbit the Earth,they are always over the same geographicpoint on the Earth's surface.

Polar OrbitThey orbit from pole to pole with asynchronized period. As they move in theirorbits, they scan swaths of the Earth'ssurface. They pass over any given pointtwice a day. Their operational lifetime isapproximately two years.

GOES EAST

Orbital altitude

Weight

Launch date

Orbit

22,370 miles (36,000 km)

4,850 pounds (2,200 kg)

2001

75°

12 feet(3.6 m)

88 feet(26.9 m)

AREA OF LEASTHEAT EMISSION

AREA OF GREATESTHEAT EMISSION

YELLOWLow clouds

DARK ZONESLow reflectivity

ORANGEDry andmountainous

WHITEHigh clouds

GREEN Vegetation

CLEAR ZONESHighreflectivity

ACTIVE POLAR SATELLITES ACTIVE GEOSTATIONARY SATELLITES

CHARACTERISTICS

ORBITAL ALTITUDE

ROTATIONAL VELOCITY

ORBITAL PERIOD

22,300 miles (35,900 km)

100 RPM

24 hours

GEOSTATIONARYORBIT22,245 miles(35,800 km)

ACCOMPANYINGTHE EARTH1,100 miles per second(1,770 km/sec)The velocity necessaryto remain fixed over onepoint on the Earth

Solarsail

Sensors

Climate Change

Mountain glaciers are melting,and this is a threat to theavailability of freshwater. Itis calculated that 8 cubicmiles (35 cu km) of water

melts from the glaciers each year, which isthe glaciers' major contribution to raisingthe global sea level; it is thought that thecontinental ice sheet may play a significantlylarger role. The volume of the glaciers in the

European Alps and in the CaucasusMountains has been reduced by half, and inAfrica, only 8 percent of the largest glacier ofMount Kenya still exists. If these tendenciescontinue, by the end of the century, most

glaciers will have disappeared completely,including those in Glacier National Park inthe United States. That will have powerfulrepercussions on the water resources ofmany parts of the world.

GODS AND RITUALS 76-77

CLIMATE ZONES 78-79

PALEOCLIMATOLOGY 80-81

THE PLANET WARMS UP 82-83

ACCELERATED MELTING 84-85

TOXIC RAIN 86-87

WEAKER AND WEAKER 88-89

CHANGE; EVERYTHING CHANGES 90-91

GLACIERS IN ALASKAApproximately 5 percent of the land iscovered by glaciers, which advance andbreak up when they reach the ocean,where they form impressive cliffs of ice.

GRAN ATLAS DE LA CIENCIA ENFERMEDADES Y MEDICINA 7776 CLIMATE CHANGE

Gods and RitualsP

redicting the weather was a subject of interest to all the earlycivilizations that populated the Earth. Greeks, Romans, Egyptians,pre-Columbians, and Orientals venerated the gods of the Sun, the

Moon, the heavens, the rain, storms, and the wind for centuries. In theirown way, with rituals and praise, they tried to influence the weather toimprove the bounty of the harvest.


The OrientHinduism has variousweather-related gods. The

most popular is Surya (god of thesun). Next come Chandra (god of themoon), Indra (the god who governsheaven), and Parjanya (god of rain).Japanese mythology emphasizes thefollowing: Fujin (god of wind),Amaterasu (goddess of the sun),Tsukiyomi (god of the moon),Amatsu-kami (god of heaven),Susanoo (god of storms), and Aji-Suki-Taka-Hi-Kone (god of thunder).

SURYAHindu god of the sun. InIndia the sunpersonified as Suryawas considered to beharmful by theDravidians of the southbut benevolent by thepeoples of centralregions. These peoplesattributed great healingpower to the god.

The RomansThe Romans worshiped many godsbecause they inherited them from the

Greek oracles. The gods of weather wereJupiter (wise and just, who reigned over theearth), Apollo (the god of the sun), Neptune(the god of the sea and storms), andSaturn (the god of agriculture). Each godhad a specific function. As a result, anyhuman activity could suffer or benefitfrom the attitude of the god in chargeof that particular function. Thus, thepurpose of ritual worship and sacrificeto the gods was to gain their favor.

EgyptiansAs in all ancient civilizations,the gods of weather were

very much a part of Egyptian life.Civilization extended along thebanks of the Nile, where waterwas crucial for survival—that is,where cities, temples, pyramids,and the entire economic life of thekingdom were concentrated. Theweather influenced the rising ofthe river and the harvests.Therefore the Egyptians veneratedRe (the god of the sun), Nut (thegod of heaven), Seth (the god of the storm), and Toth (the god of the moon).

FUJINJapanese god of wind.Drawn as a darkmonster, covered withleopard skin, he carrieda bag of wind on hisshoulders.

Pre-ColumbiansThe pre-Columbian populationbelieved water was a gift from

the gods. For the Aztecs, Tlaloc was thegod of rain, whereas the Incas calledhim Viracocha. Among the Mayans, hewas known as Chac. He was the divinityof the peasants because water was the

essential factor for stability andorganization for these indigenous

peoples. The calendar made itpossible to forecast certain

astrological events andrainstorms.

VIRACOCHAFor the Incas, he wasall powerful. Creatorof the universe and ofall the earth, he waslinked with rays oflight, thunder,lightning, and snow.

CHACMayan god of agriculture. TheMayans performed ceremoniespetitioning Chac for rain whendrought threatened the harvest.

TLALOCVenerated by the Aztecs, he wasknown as the provider because hehad the power to bring rain,which made the corn grow.

THE SCEPTERA symbol of commandconsisting of ornamentedshort sticks, the symbol

of authority

REEgyptian sungod, theprimordialcreator. Hiscenter ofworship wasHeliopolis, or theCity of the Sun.

GreeksThe powerful Zeus was the king of the Greekgods and dispenser of divine justice. He was

the sovereign of heaven (his brothers Poseidon andHades governed the ocean and the underworld,respectively). He carried a thunderbolt to representhis power, associated with the weather. Zeus livedon Mount Olympus, from where he could observeand often intervene in the affairs of humans. TheGreeks believed that Poseidon, when annoyed,would break up the mountains and throw them intothe sea to form islands. Uranus was apersonification of heaven for the Greeks, and Apollowas the god of the sun, light, and creation.

ZEPHYRUSThe Greek god of the westwind had an importantpresence. At times he wasbeneficial, and at othertimes catastrophic. Thoughthe ancient Greeks were notsure whether the windswere male or female, theydid believe the winds hadwings.

SETHEgyptian godof the storm,representedby a jackal, adog, or a wolf.The son of Reand brother ofOsiris.

THE EAGLEJupiter is the Romansupreme god,represented by thefigure of the eagle.He is also first inwisdom and power.

THE LIGHTNING BOLTJupiter reigned over theearth and heaven, andhe had the attributes ofan eagle, a lightningbolt, and a scepter.

78 CLIMATE CHANGE WEATHER AND CLIMATE 79

TROPICALHigh temperatures throughoutthe year, combined with heavyrains, are typical for thisclimate. About half of theworld's population lives inregions with a tropical climate.Vegetation is abundant, andhumidity is high because thewater vapor in the air is notreadily absorbed.

COLDVery cold winters, withfrequent freezing at night,are typical of these regions.In these zones, the climatechanges more often thananywhere else. In most coldclimate regions, thelandscape is covered bynatural vegetation.

POLARMOUNTAINOUSCLIMATEMountains create their ownclimate that is somewhatindependent of their location.Near the poles, the polar climateis dominated by very lowtemperatures, strong andirregular winds, and almostperpetual snow. The mountainpeaks lack vegetation.

DRYLack of rain controls the aridclimate in desert orsemidesert regions, the resultof the atmosphericcirculation of air. In theseregions, dry air descends,leaving the sky clear, withmany hours of burning Sun.

In 1936 Russian-bornclimatologist Wladimir

Köppen presented aclimatological classificationbased on temperature andprecipitation. The table providesa broad overview of theapproximate distribution ofclimates on the terrestrial globe.Köppen classification does notdiscuss climatic regions butrather the type of climate foundin a given location according tospecific parameters.

J F M A M J J A S O N D

1,000

500

250

0

40

20

0

-20

MANAUS, BRAZILAnnual precipitation

75 inches (1,900 mm)


1,000

500

250

0

40

20

0

-20

80°

60°

40°

20°

0°

20°

40°

60°

mm 0C

TIMBUKTU, MALIAnnual precipitation 9 inches (232 mm)


1,000

500

250

0

40

20

0

-20

mm 0CMOSCOW, RUSSIAAnnual precipitation25 inches (624 mm)

12º F(6.5º C)

is the temperature decrease forevery 3,300 feet (1,000 m) of

increase in elevation.

KEY

Tropical forests, without a dry season

Tropical savanna, with a dry winter

Steppes (semiarid)

Desert (arid)

Temperate humid, without a dry season

Temperate, with a dry winter

Temperate, with a dry summer

Tundra

is the average annualtemperature of the Earth.

59º F(15º C)

0Cmm

Indian

Ocean

Atlantic

Ocean

Pacific

Ocean

Co

rd

il

le

r a

de

lo

sA

nd

es

A l p s

Ro

ck

yM

ou

n

t a

in

s

A p p a l a c h i a

n

Mou

nt a

in

s

H im

ala

ya

s

S a h a r aA r a b i a n

P e n i n s u l a

G i b s o nD e s e r t

C o n g ob a s i n

Amazonbasin

P a t a g o n i a

P a m p a sr e g i o n

E a s t E u r o p e a nP l a i n

P l a i n s o fS i b e r i a

S i b e r i a

Fruit trees

HudsonBay

Ice cap

Black SeaCaspian

Sea

TEMPERATECharacterized by pleasanttemperatures and moderaterains throughout the year.Winters are mild, with long,frost-free periods.Temperate regions are idealfor most agriculturalproducts.


1,000

500

250

0

40

20

0

-20

Climate Zones

RAINFOREST OR JUNGLE

Plentifulwatersources

Tropical fruitsand flowers

Green andfertile soil

Layers ofvegetation

AgricultureNaturalbrush

Fertile soil,stable climate

Humansettlements

Dry soil

Sand

Intermittentwater

Sparsevegetation

DESERT

TUNDRA AND TAIGA

Lichens

Eternal snow onthe mountains

Sparseconifers

Juniperbrush

Deciduoustrees

Lakes

Coniferousforest

FORESTS AND LAKES

Glacial

Mountain climate

Temperate cold continental(hot summer)

Temperate cold continental(cold summer)

Temperate cold continental(subarctic)

Latitudes

N O R T HA M E R I C A

C E N T R A LA M E R I C A

S O U T HA M E R I C A

A F R I C A

A S I A

O C E A N I A

mm 0C

E U R O P E


1,000

500

250

0

40

20

0

-20

mm 0C

LHASA, TIBETAnnual precipitation 16 inches (408 mm)

HOUSTON, U.S.Annual precipitation of 46 inches (1,170 mm)

Sea of dunes

Different places in the world, even if far removed from each other,can be grouped into climate zones—that is, into regions that arehomogeneous relative to climatic elements, such as temperature,

pressure, rain, and humidity. There is some disagreement amongclimatologists about the number and description of each of these regions,but the illustrations given on this map are generally accepted.

PLAINS ANDURBANIZATION

Köppen Climate Classification

Temperature and RainsThe temperature of the Earth depends on the energy from the Sun, which isnot distributed equally at all latitudes. Only 5 percent of sunlight reaches the

surface at the poles, whereas this figure rises to 75 percent at the Equator. Rain isan atmospheric phenomenon. Clouds contain millions of drops of water, which collideto form larger drops. The size of the drops increases until they are too heavy to besupported by air currents, and they fall as rain.

B.Y.A. = billions of years ago M.Y.A. = millions of years ago Y.A. = years ago

PaleoclimatologyT he climate of the planet is constantly changing. In approximately two million

years, the Earth has gone through very cold periods, or glaciations, that lastedthousands of years, alternating with warm periods. Today we live in an

interglacial period that began some 10,000 years ago with an increase in averageglobal temperature. These climatic changes can be analyzed over time periodsthat exceed hundreds of thousands of years. Paleoclimatology uses recordsderived from fossils, tree rings, corals, glaciers, and historicaldocuments to study the climates of the past.

WEATHER AND CLIMATE 8180 CLIMATE CHANGE

Inhabitants

Year of founding

Temperature

Surface

Surface area of the lake

Only scientists

1957

-67° F (-55° C)

95% ice

5,405 square miles(14,000 sq km)

VOSTOKLatitude 77° S

Longitude 105° E

SAMPLESThe zones marked on themap are places wherescientists have gatheredsamples of ice, which wereanalyzed in the laboratories.

Gas MeasurementVertical ice cores (or samples) allowscientists to study the climate of

the past. The nearly 12-foot-long (3.6-m) ice sample taken at the RussianVostok station contains climaticdata going back 420,000 years,including the concentration ofcarbon dioxide, methane, andother greenhouse gases in theatmosphere.

CLOTHESprotect the scientists fromthe weather and prevent thecontamination of samples.

ChronologyDuring the history of theEarth, climate has changed

greatly, which has had a large effectnot only on the appearance of the

Earth's surface but also on animaland plant life. This timeline shows theplanet's major climate changes andtheir consequences.

4.5 B.Y.A.In the beginning,there was heat. Lifeproduces oxygen andcools the climate.

2.7-1.8 B.Y.A.Ice covers veryextensive areas.

544 M.Y.A.Glacial climate in achanging geography.Extinction of 70 percentof marine species.

330 M.Y.A.Beginning of a longperiod of glaciation.Ice covers differentgeographic areas.

245 M.Y.A.Drought and heat at thebeginning. Abruptcooling at the end of theperiod. Appearance ofthe dinosaurs.

65 M.Y.A.Paleocene andbeginning Eocene: verywarm climate. MiddleEocene: cooling begins.

2 M.Y.A.The cold continues;glaciation occursevery 100,000 years.

18,000 Y.A. begins the lastdeglaciation. Increase in temperature;melting of ice.

1,300-700 Y.A.Medieval warm period;in some places warmerthan today. Vikingsarrive in Greenland..

550-150 Y.A.Little Ice Age. Alpineglaciers advance; moresevere winters.

1.6 M.Y.A.Interglacial. Thebeginning of a two-million-year period.

Dronning Maud Land

South Pole

Dominion Range

Newall glacier

Talos Dome

Law Dome

VOSTOK

RIDS

LittleAmerica

Siple Station

KEY

Drillings

Ice sheets

EVALUATION OF GREENHOUSE GASES

00.28 0.8 1.7

280

350

0.28 0.31

Year 1990

Year 1770400

300

200

100

0

Parts permillion

Halocarbons Methane Carbondioxide

Nitrousoxide

Human ActivityClimate can be divided into before and after the IndustrialRevolution. This graphic shows the progressive increase of

halocarbon gases, methane, carbon dioxide, and nitrous oxidebetween 1770 and 1990. It is clear that humans have contributedto the contamination of the planet.

CompositionThe lower graphic shows the change in concentration ofmethane in the atmosphere in the last 20,000 years until the

end of the preindustrial era. The information collected was estimatedon the basis of ice probes in Greenland and Antarctica.

METHANE CONCENTRATION

Antarctica

Greenland

0.80.70.60.50.40.3

0

Parts permillion

Time in years before the present

0 2.000 4.000 6.000 8.000 10.000 12.000 14.000 16.000 18.000 20.000

Holocene Glaciation

174 (53 m)

Feet 177(54 m)

6,024(1,836 m)

6,027(1,837 m)

10,007(3,050 m)

10,010(3,051 m)

ICE CORESSamples are taken at different depths.The surface snow becomes morecompact in the lower layers. In thelast layer, there are rocks and sand.

280

350

82 CLIMATE CHANGE

The Planet Warms UpT he increase in average temperature of the Earth's atmosphere and oceans is the result of

global warming. The main cause is an increase in carbon dioxide emissions by industrializednations during the past 200 years. This phenomenon has increased the greenhouse effect. It

is estimated that the average global temperature has increased more than 1.1° F (0.6° C)between the end of the 19th century and the year 2000. The consequences of this arealready beginning to be noticed. Changes are observed in the global distribution ofprecipitation: there are regions where there is an increase of rain, and there are otherregions where rain is diminishing. This generates, among other things, a redistributionof fauna and flora, changes in ecosystems, and changes in human activities.


Our planet is going through an acceleratedprocess of global warming because of the

accumulation in the atmosphere of a series of gasesgenerated by human activity. These gases not onlyabsorb the energy emitted by the surface of theEarth when it is heated by radiation coming from theSun, but they also strengthen the naturally occurringgreenhouse effect, whose purpose is to trap heat. Oneof the primary agents responsible for the growth ofthe greenhouse effect is CO2 (carbon dioxide), whichis artificially produced by burning fossil fuels (coal,petroleum, and natural gas). Because of the intensiveuse of these fuels, there has been a notable increasein the quantity of both carbon and nitrogen oxides

and carbon dioxide released into the atmosphere.Other aggravating human activities, such asdeforestation, have limited the regenerative capacityof the atmosphere to eliminate carbon dioxidethrough photosynthesis. These changes have caused aslow increase in the average annual temperature ofthe Earth. Global warming, in turn, causes numerousenvironmental problems: desertification and droughts(which cause famines), deforestation (which furtherincreases climate change), floods, and the destructionof ecosystems. Because all these variables contributeto global warming in complex ways, it is very difficultto predict with precision everything that will happenin the future.

Product of Human Activity

With the changing patterns of precipitation andthe shifting of air-pressure systems, some regions

will become more humid, and others will sufferdroughts. One of the areas that will become drier willbe the western part of North America, wheredesertification is already affecting agriculture.According to current forecasts, areas in high latitudes,closer to the poles, will go through a rapid warming inthe next 40 years. Populations of animals will be forcedto emigrate from their habitat to avoid extinction, andother animals, such as the polar bear and emperorpenguin, will have trouble subsisting as their habitatsdisappear. Ocean levels are rising between 0.4 and 0.8inch (1 and 2 cm) per decade. Some Pacific islandnations such as Tuvalu have contingency plans forevacuation. Another affected region is the Great BarrierReef of Australia. The coral is very sensitive to changesin temperature. At temperatures above a normal 84° F[29 ° C], the coral begin to expel the algae on whichthey depend for food, and then they die.

A Different World

Activities, such as the burningof fuels and deforestation,increase the concentration ofgreenhouse gases.

Increase of thenatural greenhouseeffect of theatmosphere

The modified atmosphereretains more heat emitted bythe Earth and thus upsets thenatural equilibrium.

APPROXIMATE INCREASEOf the Earth's global average temperature from 1860

1.1º F (0.6º C)

The discoloration of coral occurswhen the temperature exceeds84° F (29° C). Algae are lost, thecoral weakens, and the color ofthe coral fades.

84º F(29º C)

Ozonelayer

10 kmA

TM

OS

PH

ER

ES

OLA

R E

NE

RG

Y

50 km2 km

OZONEThe ozone layer is inthe stratosphere, abovethe surface of theplanet. It acts as apowerful solar filterthat prevents thepassage of all but asmall amount ofultraviolet radiation(UV).

THE TEMPERATURE OF THE EARTH THROUGH THE YEARSThe effects of global warming are already noticeable. It is estimated that the average global temperaturehas increased more than 1.1° F (0.6° C) between the end of the 19th century and the year 2000.

INCREASE OFPRIMARY

GREENHOUSEGASES

Surface

Types of reefs

Age

Discovery

1,430 miles (2,300 km)

3,000

300 million years

1770, by James Cook

GREATBARRIER REEF Latitude 18°S

Longitude 147°E

LOW

TR

OP

OS

PH

ERE

Trop

opau

se

STR

ATO

SP

HER

E

Stra

topa

use

1

23

84 CLIMATE CHANGE

Accelerated Melting

The climate is changing at a disconcerting speed. Glaciersare retreating, and sea level is rising because of aphenomenon known as thermal expansion. Scientists

evaluating the planet's health deduce that this is theconsequence of the Earth warming too rapidly. Humanactivity—in particular, the burning of fossil fuels andthe consequent accumulation of greenhouse gasesin the atmosphere—has increased this trend.


ARCTICLatitude 66° N

Longitude 0°

Surface area

Depth

Temperature

5,444,040 square miles (14,100,000 sq km)

13,100 to 6,600 feet (4,000 to 2,000 m)

-58° F (-50° C) in winter

ADVANCING WATERS

The accelerated melting raises sealevel and floods coasts that have a

gentle slope. As the sea levelrises, the width of

coastal areasdiminishes.

Melting of the icewill be detrimentalto people andanimals living in theArctic.

GULF STREAM originates in the Gulf of Mexicoand carries warm water tohigher latitudes.

OCEANCURRENTS The main cause ofchanges in oceancurrents are changesin the water's salinity.

ADVANCE OFVEGETATIONThe retreat of the iceleaves organicmaterial exposed,which, instead ofreflecting solarradiation, absorbs it,increasing globaltemperature.

PROJECTIONS2010-30

Summer sea ice,currently in decline,tends to diminishmore and more rapidlyin the future.

2040-60

As the centuryprogresses, sea icecontinues to meltmore and more alongthe coasts of theArctic Ocean.

2070-90

Some scientific modelsproject that summersea ice will be virtuallyeliminated during thiscentury.

Barents

Sea

Bering

Strait

Hudson

Bay

Greenland

North

America

Europe

EFFECT The Arctic heats up more rapidly than theglobal average because of the darkness ofthe soil and the water, which, once exposed,trap more heat from the atmosphere. Once exposed to the

air, the CO2 is absorbedby the atmosphere.

POSSIBLE FLOOD ZONES

In the period between 1993 and2003, some coastlines werereduced by the rise in sea level.

164 feet(50 m)The amount of coastalarea lost when sea levelrises 20 inches (50 cm)

70%of the freshwaterin the world is inAntarctica.

LABRADORCURRENT starts in the Arcticand moves south,carrying cold waterand loose ice.

PacificOcean

Atlantic Ocean

50 cm

50 m

Why It HappensThe thawing at the poles is, in part, caused by theincrease of greenhouse gases. They absorb the

radiation emitted by the Earth and heat up theatmosphere, further increasing the Earth's temperature.The melting of glaciers puts more water in the oceans.

AntarcticaThe Antarctic loses 36 cubic miles (152 cukm) of ice per year, and the western ice sheet

is becoming thinner at an accelerating pace. This iscontributing to increases in sea level. Over the longterm, the effect on the climate could be disastrousfor many regions of the planet.

5.

These particles rise tothe surface, convertedinto CO2.

4.

Sunlightreflectsfromlayersof ice.

1. Where the ice isthe thinnest, orcracked, radiationpenetrates to theocean.

2.

Ice absorbs the heat fromsunlight and releases agreat quantity of trappedcarbon particles.

3.

Particles of CO2

Via cracks in the ice, new marine routescan develop. When ships pass, the cracksrarely close, increasing the process ofheat absorption and the release of CO2.

80%of Greenland's ice is losing 3 feet(1 m) per year.

TEMPERATUREINCREASEIt is believed that theincreased emission ofgreenhouse gases willcause an increase inaverage globaltemperature ofbetween 3.2° and 7.2° F(1.8° and 4.0° C) overthe next 100 years.

-25 -15 -5 0 5 15 25

WEATHER AND CLIMATE 8786 CLIMATE CHANGE

Burning fossil fuel releases into the air chemicals that mix with water vaporand produce acid rain. The excess of sulfur dioxides and nitrogen dioxides inbodies of water makes the development of aquatic life more difficult,

substantially increasing the mortality rate of fish. Likewise, it affects vegetation onland, causing significant damage in forested areas by contaminating animals anddestroying substances vital for the soil. Moreover, acidic sedimentation can increasethe levels of toxic metals, such as aluminum, copper, and mercury, that are depositedin untreated drinking-water reservoirs.

Toxic Rain

LEAVESThis rain damages theirsurface, causing smalllesions that alter theaction of photosynthesis.Fir Beech Oak

Areas under cultivation arenot as vulnerable becausethey are generally improvedby fertilizers that restorenutrients to the soil andneutralize acidity.

Melting water carriesacidic particles thatcome from the rain.

Seriously affectedspecies are lettuce andtobacco, especiallybecause their leaves,destined for humanconsumption, must beof high quality.

Acid rain acts via certainmechanisms that weakenplants, making them morevulnerable to the effects ofwind, cold, drought,disease, and parasites.

In mountainous areas, fog andsnow contribute significantquantities of the gases in question.

The acidity of rainwaterchanges the neutral pH ofbodies of water.

MOST-THREATENED SPECIES

CONSEQUENCESFOR PLANTS

CONSEQUENCESFOR AGRICULTURE

EFFECTS ON THE WATER

SOILCONSEQUENCES

Atmospheric circulation enhancesthe dispersal of contaminantsover great distances.

AREAS AFFECTED BY ACID RAIN

WHAT IS pH?

The degree ofacidity of anaqueous solution.It indicates theconcentration ofhydrogen ions.

pHneutral

pHacid

Destructionof chlorophyll

Defoliation

1972 The year when thephenomenon of acid rain wasrecorded for the first time

Petroleumrefineries

SILICATE SOILThe effect of acidityincreases because of the lackof buffering minerals.

CALCAREOUS SOILThe effect is neutralized bythe presence of bicarbonate.

Rootdamage

The leaves losetheir wax layer.

pH:6Normal rain

pH:5Acid rain

pH 7(neutral)

pH 4.3(acid)

1GAS EMISSIONS

Generated by burning fuelsand the eruption of volcanoes

Wasteincinerator

Chemicalindustry

NO2COH2SCH4SO2CO2

4ACID RAINfalls in the form of water, fog, ordew and leaves the acids formed inthe atmosphere on the ground.

The regions most vulnerable to this phenomenon areMexico, Beijing, Cairo, Jakarta (Indonesia), and LosAngeles.

2GAS MIXTURESThe molecules of variousgases rise and mix withwater in the air.

3PHOTOCHEMICALREACTIONSunlight increases the speed atwhich chemical reactions occur. Thus,sulfur dioxide and atmospheric gasesrapidly produce sulfur trioxide.

pH 4.3 LEVEL AT WHICH FISH DONOT SURVIVE IN THE WATER Trout Perch Frogs

MOST-AFFECTED SPECIES

TYPES OF GASES EMITTED

Chemicalindustry

CO2 , SO2 ,H2S (hydrogen sulfide)

Wasteincinerator

CO2 , SO2 , CH4 ,CO (carbon monoxide)NO2 (nitrogen dioxide)

CO2 (carbon dioxide)SO2 (sulfur dioxide)CH4 (methane)

Petroleumrefinery

88 CLIMATE CHANGE

Weaker and Weaker

Artificial substances are destroying the ozone layer, whichprovides protection against ultraviolet rays. This phenomenonis observed every year in polar regions (primarily in the

Antarctic) between August and October. Because of this, the Earthis receiving more harmful rays, which perhaps explains theappearance of certain illnesses: an increase in skin cancer cases,damage to vision, and weakening of the immune system.

UV RADIATION

Ultraviolet radiation (UV) is a radiant form of energy that comes from the Sun.The various forms of radiation are classified according to the averagewavelength measured in nanometers (nm), equivalent to one millionth of amillimeter. The shorter the wavelength, the greater the energy of the radiation.

CFC GASESare a family of gases withmultiple applications. Theyare used in refrigerationsystems, air-conditioningequipment, and aerosols.

WHEN? WHO? HOW?In 1974, it was discovered that industrialchlorofluorocarbons (CFCs) affect theozone layer. Chemists Mario Molina and F.Sherwood Rowland demonstrated thatindustrial CFCs are the gases thatweaken the ozone layer by destroying theozone molecules.

UV-AThese rays easilypenetrate the ozonelayer. They cause skinwrinkling and aging.

HUMAN BEINGSSkin cancer. Damage tovision. Weakening of theimmune system. Severeburns. Skin aging.

ANIMALSDiseases among farmanimals. Destruction oflinks in the food chain.Increase of skin cancer.

PLANTSDestruction of phytoplankton.Inhibition of the photosynthesisprocess. Changes in growth.Reduced harvest yields.

UV-Bare almost all absorbedby the ozone layer.They are harmful andcause various types ofskin cancer.

UV-CThese are the mostdamaging rays, butthey are totally filteredby the upper part ofthe ozone layer.

HOW IT DETERIORATES

Ultraviolet radiation strikesa molecule of CFC gas.

1

An atom ofchlorine isreleased.

2

3 4 The chloromonoxidecombines with anatom of freeoxygen and releasesthe chlorine atom.

5 This atom, onceagain free,combines withanother moleculeof ozone.

WWEATHER AND CLIMATE 89

THE SOUTHERN OZONE HOLEThe thinning of the ozone layer overthe Antarctic is the result of a seriesof phenomena, including the action ofchlorine radicals, which cause thedestruction of ozone.

200011,000,000 square miles

(28,000,000 sq km) 200110,000,000 square miles

(26,000,000 sq km)2004

9,300,000 square miles(24,200,000 sq km)

200510,400,000 square miles

(27,000,000 sq km)

50 to 100THE NUMBER OF YEARSTHAT CFC GASES SURVIVEIN THE ATMOSPHERE

11,000,000square miles

(28,000,000 sq km)is the size of the area of

attenuated ozone reached in 2000.

75%OF SKIN CANCERIS ATTRIBUTED TOUV-B RADIATION.

O2 O3

Ultraviolet rays strike a molecule of oxygen whichbreaks up and releasesits two atoms.

One of the releasedatoms combines witha molecule of oxygen.Together they form amolecule of ozone.

One of the releasedatoms combines witha molecule of oxygen.Together they form amolecule of ozone.

The process canstart again withthe new oxygenmolecule.

1 2 3

4

HOW OZONE IS FORMED

The ozone layerfunctions as anatural filter,absorbing UV rays.

It is popularly calledthe ozone hole—adecrease or abnormalthinning that occursin the ozone layer.

OZONE LAYERAt an altitude of 12 to 19 miles (20 to 30km), the Earth is surrounded by astratospheric ozone layer that is of vitalimportance for life on the surface. The layeris formed from oxygen molecules throughthe absorption of ultraviolet light from theSun. This reaction is reversible, that is, theozone can return to its natural state, oxygen.This oxygen is reconverted into ozone,beginning a continuous process of formationand destruction of these components.

Ozone layer

Troposphere

Mesosphere

Exosphere

Stratosphere

Chlorine atoms combinewith a molecule of ozone,destroy it, and form onechloromonoxide and oneoxygen atom.

90 CLIMATE CHANGE WEATHER AND CLIMATE 91

Cause and EffectThe burning of fossil fuels and theindiscriminate cutting of deciduous forests

and rainforests cause an increase in theconcentration of carbon dioxide, methane, andother greenhouse gases. They trap heat andincrease the greenhouse effect. That is howthe Arctic is warming up; the density ofthe ice is decreased by melting, andfreshwater flows into the ocean,changing its salinity.

THINNING OF THE OZONE LAYERThe ozone layer protects us from ultraviolet rays, but, because of the release of artificial substances, it is thinning out. This phenomenon is observed each yearover Antarctica between August and October and overthe North Pole between October and May. Moreover,there is evidence that greater amounts of UV rays atthe Earth's surface are destroying or altering vegetablecells and decreasing the production of oxygen.

THE EFFECT OF POLAR MELTINGThe snow-covered sea ice reflectsbetween 85 and 90 percent of thesunlight that strikes it, whereas seawater reflects only 10 percent. Forthat reason, as the ice and snow melt,many of today's coastlines willbecome submerged under water,which will cause yet more ice to melt.

Rays that pass throughthe ozone layer

The ozone layer stopsultraviolet rays.

SURFACE OFTHE EARTH

Normal thicknessof the ozone layer

Hole in theozone

More than 10.8° F(6° C)

From 9° to 10.8° F(5° to 6° C)

From 7.2° to 9° F(4° to 5° C)

From 5.4° to 7.2° F(3° to 4° C)

From 3.6° to 5.4° F(2° to 3° C)

From 1.8° to 3.6° F(1° to 2° C)

ACCELERATION OF THEGREENHOUSE EFFECTIce reflects solar radiation, whereasthe soil of jungles, forests, andsteppes absorbs the energy andradiates it as sensible heat. Thisartificially increases the greenhouseeffect and contributes to globalwarming.

Long-wave radiationemitted by the Earth istrapped by the atmosphere.

Energy isintegrated into theclimatic system.

SURFACE OFTHE EARTH

Incidentrays

ATMOSPHERE

The Most ResponsibleThe climate of the planet is constantlychanging. At present, the average global

temperature is approximately 59° F (15° C).Geologic and other types of evidence suggest thatin the past the average could have been as low as45° F (7° C) and as high as 81° F (27° C). Climatechange is, in large part, caused by human activities,which cause an increase in the concentration ofgreenhouse gases. These gases include carbon dioxide,methane, and nitrogen dioxide and are released by modernindustry, by agriculture, and by the burning of coal, petroleum,and natural gas. Its atmospheric concentration is increasing:atmospheric carbon-dioxide content alone has grown by more than20 percent since 1960. Investigators indicate that this warming canhave grave implications for the stability of the climate, on which most ofthe life on the planet depends.

THE RISE INTEMPERATUREIn Alaska and western Canadawinter temperatures haveincreased between 5.4° and 7.2° F(3° and 4° C) in the past 50years. It has been projected thatin the next 100 years the Earth'saverage temperature willincrease between 3.2° and 7.2° F(1.8° and 4.0° C).

Warm marine current

CO2 isreleased

THE ICYCOASTLINE

Solar rays

OCEAN

Change; Everything Changes

Indian

Ocean

Atlantic

Ocean

Pacific

Ocean

100years

is the length of time ittakes for a deciduousforest to return to itsnatural state after ithas been laid to waste.

N O R T HA M E R I C A

C E N T R A LA M E R I C A

S O U T HA M E R I C A

E U R O P E

A F R I C A

A S I A

O C E A N I A

92 GLOSSARY WEATHER AND CLIMATE 93

Glossary

AccretionGrowth of an ice crystal in the atmosphere bydirect capture of water droplets when thetemperature is below 32° F (0° C).

Acid RainRain resulting from the mixture of water vaporin the air with chemical substances typicallyreleased by the combustion of fossil fuels.

AerosolAerosols are very small (liquid or solid) particlessuspended in the atmosphere, with variedchemical composition. Aerosols play an essentialrole in the formation of clouds by acting ascondensation nuclei. They are also important tothe Earth's radiation balance since they help toincrease the reflection and dispersion ofradiation coming from the Sun.

Air MassExtensive volume in the atmosphere whosephysical properties, in particular thetemperature and humidity in a horizontal plane,show only small and gradual differences. An airmass can cover an area of a few million squaremiles and can have a thickness of several miles.

AlbedoA measure of the percentage of radiationreflected by a surface.

AltitudeHeight relative to sea level.

AnemometerInstrument for measuring wind velocity.

AnticycloneRegion where the atmospheric pressure isrelatively high compared with neighboringregions. Normally the air above an anticyclonedescends, which prevents clouds from formingat medium and high levels of the atmosphere.Hence an anticyclonic system is associated with

good weather.

AtmosphereThe gaseous envelope that surrounds the Earth.

Atmospheric PressureThe pressure or weight exerted by theatmosphere at a specific point. Its measurementcan be expressed in various units: hectopascals,millibars, inches, or millimeters of mercury (Hg).It is also called barometric pressure.

AuroraA phenomenon that is produced in the higherlayers of the atmosphere at polar latitudes. Anaurora occurs when there is a collision betweenthe electrically charged particles emitted by theSun and the magnetic field of the Earth. In theNorthern Hemisphere, the phenomenon is calledthe aurora borealis, and in the SouthernHemisphere, it is known as the aurora australis.

AvalancheA large mass of snow that flows down the sideof a mountain.

BarometerAn instrument for measuring atmosphericpressure. A decrease in pressure usually meansthat storms are on the way. Increasing pressureindicates good weather.

Beaufort ScaleA scale invented at the beginning of the 19thcentury by a British sailor, Francis Beaufort, forestimating and reporting wind velocity. It isbased on the different shapes taken by waterwaves at different wind velocities, and itsgraduation goes from 0 to 12. There is also aBeaufort scale for application on land based onobservations of the wind's effect on trees andother objects.

Carbon DioxideAn odorless, colorless gas emitted in the engine

CondensationThe process by which water vapor istransformed into liquid by the effect of cooling.

ConductionThe transfer of heat through a substance bymolecular action or from one substance toanother it is in contact with.

ContinentalityThe tendency of the interior regions of thecontinents to have more extreme temperaturechanges than coastal zones.

ConvectionThe process by which a heated surfacetransfers energy to the material (air, water, etc.)above it. This material becomes less dense andrises. Cooler material descends to fill in the void.Air rising as a result of the heating of theground by the Sun's rays.

Coriolis ForceA fictitious or apparent force that applies whenthe Earth is used as a reference frame formotion. It depends upon the latitude and thevelocity of the object in motion. In the NorthernHemisphere, the air is deflected toward theright side of its path, and in the SouthernHemisphere, the air is deflected toward the leftside of its path. This force is strongest at thepoles and does not exist at the Equator.

CycloneA climatic low-pressure system.

DesertA hot or cold zone where annual precipitation isless than 1 inch (25 mm).

DesertificationA process that converts fertile land to desert

through a reduction in precipitation.

DewCondensation in the form of small drops ofwater formed on grass and other small objectsnear the ground when the temperature hasdropped to the dew point. This generallyhappens during the night.

DikeAn earthwork for containing or channeling ariver or for protection against the sea.

DrizzleA type of light liquid precipitation composed ofsmall drops with diameters between 0.007 and0.019 inch (0.2 and 0.5 mm). Usually drizzlefalls from stratus-type clouds that are found atlow altitudes and can be accompanied by fog,which significantly decreases visibility.

DroughtAn abnormally dry climatic condition in aspecific area where the lack of water isprolonged and which causes a serioushydrological imbalance.

El NiñoThe anomalous appearance, every few years,of unusually warm ocean conditions along thetropical west coast of South America.

ErosionAction in which the ground is worn down bymoving water, glaciers, wind, or waves.

EvaporationPhysical process by which a liquid (such aswater) is transformed into its gaseous state(such as water vapor). The reverse process iscalled condensation.

ExosphereThe outermost layer of the Earth's atmosphere.

Flash FloodSudden flooding caused by the passage of alarge quantity of water through a narrow space,such as a canyon or a valley.

FogVisible manifestation of drops of watersuspended in the atmosphere at or near groundlevel; this reduces the horizontal visibility to lessthan a mile. It originates when the temperatureof the air is near the dew point, and sufficientnumbers of condensation nuclei are present.

ForecastA statement about future events. The weatherforecast includes the use of objective modelsbased on a number of atmospheric parameterscombined with the ability and experience ofthe meteorologist. It is also called weatherprediction.

FrontThe transition or contact zone between twomasses of air with different meteorologicalcharacteristics, which almost always impliesdifferent temperatures. For example, a frontoccurs at the area of convergence betweenwarm humid air and dry cold air.

FrontogenesisThe process of formation or intensification of afront. This happens when wind forces twoadjacent masses of air of different densities andtemperatures together, creating a front. It canoccur when one of the masses of air, or both,move over a surface that reinforces theiroriginal properties. This is common on the eastcoast of North America or Asia, when a mass ofair moving toward the ocean has a weak orundefined boundary. It is the opposite offrontolysis.

exhaust of automobiles, trucks, and buses. It isalso produced by the combustion of coal andother organic material. Too much carbon dioxidein the atmosphere contributes to globalwarming.

ChlorofluorocarbonsArtificial chemical substances often contained inaerosols, refrigerants, and air conditioners.These chemicals are largely responsible for thedamage to the ozone layer.

CirrusWispy cloud formations at altitudes greaterthan 16,400 feet (5,000 m).

ClimateThe average state of the meteorologicalconditions of a location considered over a longperiod of time. The climate of a location isdetermined by climatological factors: latitude,longitude, altitude, topography, andcontinentality.

CloudA visible mass of small particles, such asdroplets of water and/or crystals of ice,suspended in the air. A cloud is formed in theatmosphere because of the condensation ofwater vapor onto solid particles of smoke, dust,ashes, and other elements called condensationnuclei.

CoalescenceThe process of growth of drops of water in acloud. Two drops collide and remain joined afterthe collision, constituting a bigger drop. This isone of the mechanisms that explains the growthof the size of drops in a cloud until precipitation(rain) is produced.

Cold WaveA rapid drop in temperature to the pointrequiring special protective measures inagriculture, industry, commerce, or socialactivities.

94 GLOSSARY WEATHER AND CLIMATE 95

FrostA covering of ice crystals on a cold object.

Global WarmingThe heating of the atmosphere caused byincreased concentrations of greenhouse gasesdue to human activities.

Greenhouse EffectA phenomenon explained by the presence ofcertain components in the atmosphere(primarily carbon dioxide [CO2], water vapor,and ozone) that absorb a portion of the infraredradiation emitted by the surface of the Earthand simultaneously reflect radiative energy backto the surface. This process contributes to theincrease in the average temperature near thesurface.

GustA rapid and significant increase in wind velocity.The maximum velocity of the wind must reachat least 16 knots (18 miles per hour [30 km/h]),and the difference between the peaks and calmmust be at least 10 knots (12 miles per hour [18km/h]). It generally lasts less than 20 seconds.

HailPrecipitation that originates in convectiveclouds, such as the cumulonimbus, in the form ofmasses or irregular pieces of ice. Typically hailhas a diameter of 0.2 to 2 inches (5 to 50 mm)but may grow significantly larger. The smallestice fragments—whose diameter is 0.2 inch (5mm) or less—are called small hailstones, orgraupel. Strong upward currents are requiredinside the clouds for hail to be produced.

Heat WaveA period of abnormally hot and uncomfortableweather. It can last from a few days to anumber of weeks.

HectopascalA pressure unit equal to 100 pascals andequivalent to 1 millibar—a millibar beingequivalent to 0.031 inch (0.8 mm) of ordinary

mercury. The millibar (mb) was the technicalunit used to measure pressure until recently,when the hectopascal was adopted. The pascalis the unit for pressure in the MKS system,corresponding to the pressure exerted by theunit force (1 newton) on a unit surface (1 squaremeter—11 square feet); 1,000 hPa = 1,000 mb= 1 bar = 14.5 pounds per square inch.

HighA prefix describing cloud formations at analtitude between 6,560 and 16,400 feet (2,000and 5,000 m).

HumidityThe amount of water vapor contained in the air.

HurricaneThe name for a tropical cyclone with sustainedwinds of 64 knots (74 miles per hour [119km/h]) or more, which develops in the NorthAtlantic, the Caribbean, the Gulf of Mexico, andthe Pacific Northeast. This storm is called atyphoon in the western Pacific and a cyclone inthe Indian Ocean.

HygrometerAn instrument used to measure humidity.

IceThe solid state of water. It is found in theatmosphere in the form of ice crystals, snow, orhail.

Jet StreamsAir currents high in the troposphere (about 6miles [10 km] above sea level), where the windvelocity can be up to 90 meters per second(200 miles per hour). This type of structure isseen in subtropical latitudes in bothhemispheres, where the flow is toward the east,reaching its maximum intensity during thewinter.

LatitudeA system of imaginary parallel lines thatencircle the globe north and south of theEquator. The poles are located at 90° latitude

pressure, precipitation (rain, snow, etc.), winds(velocity and direction), storms, cloud cover,percentage of relative humidity, and so on.

Ocean CurrentThe movement of water in the ocean caused bythe system of planetary winds. Ocean currentstransport warm or cold water over longdistances around the planet.

Orographic RainRain that results from the cooling of humid airas it crosses over a mountain range.

Ozone LayerA layer of the atmosphere situated 20 to 30miles (30 to 50 km) above the Earth's surfacebetween the troposphere and the stratosphere.It acts as a filtering mechanism for ultravioletradiation.

Polar FrontAn almost permanent and very large front ofthe middle latitudes that separates therelatively cold polar air and the relatively warmsubtropical air.

PrecipitationA liquid or solid, crystallized or amorphousparticle that falls from a cloud or system ofclouds and reaches the ground.

RadiationThe process by which energy propagatesthrough a specific medium (or a vacuum) viawave phenomena or motion. Electromagneticradiation, which emits heat and light, is oneform of radiation. Other forms are sound waves.

SeaquakeAn earthquake at the bottom of the ocean,causing a violent agitation of ocean waves,which in some cases reach coastal areas andcause flooding.

SnowPrecipitation in the form of white ortransparent frozen ice crystals, often in theform of complex hexagons. In general, snowfalls from stratiform clouds, but it can also fallfrom cumulus clouds, usually in the form ofsnowflakes.

StratosphereThe layer of the atmosphere situated above thetroposphere.

StratusLow clouds that form layers. They oftenproduce drizzle.

Synoptic MapA map that shows weather conditions of theEarth's surface at a certain time and place.

Thermal InversionAn inversion of the normal reduction intemperature with an increase in altitude.

ThermometerAn instrument for measuring temperature. Thedifferent scales used in meteorology are Celsius,Fahrenheit, and Kelvin (or absolute).

TornadoA column of air that rotates with great violence,stretching between a convective cloud and thesurface of the Earth. It is the most destructivephenomenon in the atmosphere. Tornadoes canoccur, under the right conditions, anywhere onEarth, but they appear most frequently in thecentral United States, between the RockyMountains and the Appalachian Mountains.

Tropical CycloneA cyclone without fronts, it develops overtropical waters and has a surface circulationorganized and defined in a counterclockwisedirection. A cyclone is classified, according tothe intensity of its winds, as a tropical

disturbance (light ground-level winds), tropicaldepression (maximum ground-level winds of 38miles per hour [61 km/h]), tropical storm(maximum winds in the range of 39 to 73 milesper hour [62 to 112 km/h]), or hurricane(maximum ground-level winds exceeding 74miles per hour [119 km/h]).

TroposphereThe layer of the atmosphere closest to theground, its name means “changing sphere,” andthis layer is where most changes in weathertake place. This is also where most of thephenomena of interest in meteorology occur.

TurbulenceDisorderly motion of air composed of smallwhirlwinds that move within air currents.Atmospheric turbulence is produced by air in astate of continuous change. It can be caused bythermal or convective currents, by differences interrain and in the velocity of the wind, byconditions along a frontal zone, or by a changein temperature and pressure.

WeatherThe state of the atmosphere at a given moment,as it relates to its effects on human activity.This process involves short-term changes in theatmosphere in contrast to the great climaticchanges that imply more long-term changes.The terms used to define weather includecloudiness, humidity, precipitation, temperature,visibility, and wind.

WindwardThe direction from which the wind is blowing.

north and south and the Equator at 0° latitude.

LightningA discharge of the atmosphere's staticelectricity occurring between a cloud and theground.

MesosphereThe layer of the Earth's atmosphere that liesabove the stratosphere.

METARThe name of the format airport meteorologicalbulletins are reported in. This includes data onwind, visibility, temperature, dew point, andatmospheric pressure, among other variables.

MeteorologyThe science and study of atmosphericphenomena. Some of the subdivisions ofmeteorology are agrometeorology, climatology,hydrometeorology, and physical, dynamic, andsynoptic meteorology.

MicrobarometerA very sensitive barometer that recordspressure variations using a magnified scale.

MistMicroscopic drops of water suspended in the air,or humid hygroscopic particles, which reducevisibility at ground level.

MonsoonA seasonal wind that causes heavy rains intropical and subtropical regions.

NormalThe standard value accepted for ameteorological element as calculated for aspecific location over a specific number of years.The normal values refer to the distribution ofdata within the limits of the commonoccurrence. The parameters can includetemperature (high, low, and divergences),

96 INDEX WEATHER AND CLIMATE 97

Index

Aabsorption, 11acid rain, 86-87

gas emissions, 86gas mixtures, 86ozone layer, weakening, 88-89pH, 87photochemical reaction, 87plant consequences, 86soil consequences, 87vulnerable regions, 87water consequences, 87

advection fog, 45aerosonde pilotless weather aircraft, 71Africa

global warming, 91potable water, 21

agricultureacid rain, 87drought, 51flooding, 48gods and rituals, 76, 77monsoons, 30tornadoes, 53

airatmosphere, 10-11circulation changes, 12-13collision, 14-15currents, 13displacement, 12weather forecast, 70

aircraft, weather, 71, 81albedo, solar radiation, 8, 9almanac, weather forecasting, 65altocumulus cloud, 39altostratus cloud, 39anabatic wind, 26Andes Mountains, 24-25anemometer, 67aneroid barometer, 66animal

acid rain, 86, 87coral, 82, 83

ozone layer thinning, 89weather folklore, 64, 65

Antarctica, 80, 81, 85anticyclone, 12, 13, 51, 68Arctic, 84-85argon, 10ash (volcanic), 9ash tree, weather folklore, 65Asia

El Niño, 33, 35 global warming, 91monsoons, 28-29, 30-31potable water, 21

atmosphere, 8climate change, 90cooling, 9disturbances, 14dynamics, 12-13global warming, 83layers, 10-11paleoclimatology, 80-81 See also ozone layer

atmospheric pressure, 66aurora, 10, 16-17Australia

drought, 50potable water, 21

autonomous underwater vehicle, 70

Bbarograph, 66barometer, 66biosphere, 8

Ccalcareous soil, 87carbon dioxide (CO2), 10

coral, 82, 83Coriolis effect, 12, 14, 22cosmic ray, 11cryosphere, 8, 9crystal, water

formation, 42snow, 42-43types, 42, 43

cumulonimbus cloud, 38, 52cumulus cloud, 14, 38current

air flow, 13cyclonic, 50formation, 22-23geostrophic balance, 22gulf stream, 85jet stream, 12, 13, 14Labrador, 85lake, 23ocean: See ocean currentsubpolar arctic circulating system, 23wind influence, 22

cyclone, 5, 12, 13, 28, 36, 57cyclonic current, 50cyclonic zone, 12-13

Ddata recorder (weather prediction), 67deep ocean current, 22-23deforestation, 82, 91depression, 13, 58, 68desert, 50, 78desertification, 5, 50, 82, 83dew, 42, 44, 65dew point, 24, 43dike, 48, 58divergence, 13donkey, weather folklore, 64droplet, formation, 20drought, 50-51

global warming, 82

water runoff, 21dry-bulb thermometer, 67dry climatic zone, 78Dust Bowl, droughts, 50

EEarth

climate change, 90-91climatic zones, 78-79equilibrium, 8-9global warming, 82-85ocean currents, 22-23paleoclimatology, 80-81rotation, 12satellite image, 6-7temperature, 82, 90-91

ecosystemdestruction, 82foundations, 8

Ekman spiral, ocean currents, 22El Niño, 32-33

conditions during, 32drought, 32-33effects, 19, 34-35flooding, 34-35

electrical storm, 46-47tornadoes, 52

embankment, 48environment, components, 6Equator, atmospheric dynamics, 12erosion, 21Europe

global warming, 91potable water, 21

evaporation, 7, 8, 20evaporimeter, 66exosphere, 10, 16

FFerrel cell, 12-13field capacity, soil, 50flood control, 48flood plain, 48flooding, 48-49

causes, 48dikes, 48, 58El Niño, 34-35embankment, 48global warming, 82, 85Hurricane Katrina, 58land, 48-49monsoons, 30-31zones, 85

fog, 44-45formation, 44radiation, 45types, 45visibility, 44

folklore, weather: See weather folkloreforecast: See weather forecastfossil fuel

global warming, 91greenhouse effect, 82

freshwater, 21, 74front, 38

cold, 14, 68occluded, 15, 68size, 15stationary, 15warm, 14, 15, 68weather map symbol, 14, 68

frontal fog, 45frost, 43Fujita-Pearson scale, 53, 54

emissions, 82, 83, 86increases, 84, 90See also greenhouse gas

CFC gas (chlorofluorocarbon gas), 88chaparral, 25Chinook wind, 26cirrocumulus cloud, 39cirrostratus cloud, 38cirrus cloud, 38, 39city, heat islands, 27climate

Köppen classification, 79temperature and rain, 78types, 78-79

climate change, 74-75, 90-91causes and effects, 91human activity, 81, 82, 90

climate zone, 78-79desert, 78forest and lakes, 79polar mountainous climate, 79rainforest, 78tundra and taiga, 79

climatic system, 6-7, 8-9cloud, 38-39

electrical storms, 46-47formation, 12, 14, 20, 38-39hurricanes, 56interior, 39lightning inside, 46rain formation, 40-41types, 11, 38, 39weather folklore, 65

cloud street, 39coastal breeze, 26, 27cold climatic zone, 79cold front, 14, 68collision (air), 14-15condensation, 7, 14, 20, 24

nuclei, 40precipitation, 8

continentality effect, 27convection, 7, 38convergence, 13, 38cooling (atmosphere), 9

98 INDEX WEATHER AND CLIMATE 99

Ggas

CFC, 88density, 10greenhouse, 8, 9, 84, 90measurement in paleoclimatology, 80

geopotential weather map, 69GEOS (Geostationary Operational

Environmental Satellite), 72-73geostrophic balance, 22glacier

accelerated melting, 74-75, 84-85Alaska, 74-75

global equilibrium, 8-9Global Positioning System (GPS), 70global warming, 82-83

accelerated melting, 84-85advancing vegetation, 85Antarctica, 85cause, 82climate changes, 5, 82effects, 82-83human activity, 82, 84predictions, 83rising ocean levels, 5, 82-83, 85

gravity, water circulation, 9Great Barrier Reef, 83greenhouse effect, 9, 10, 82-83, 91greenhouse gas, 8, 9, 81, 82, 84, 90Greenland, 81, 84ground-level weather map, 68gulf stream, 84-85

HHadley cell, atmospheric dynamics, 12, 13hail, 14, 40, 43Halley, Edmund, 68heat, greenhouse gas, 8heat island, 27

heliophanograph, 66high pressure, 12

See also anticyclonehigh pressure ridge, 69hoar frost, 43human activity

climate change, 81, 82, 90pollution, 10, 24, 90

humidity, measuring instruments, 67hurricane, 34-35, 56-57

damages, 5, 36, 58-59danger zone, 57eye and eye wall, 56formation, 56, 57hurricane hunter P3 airplane, 71preparation, 37, 60-61rotation, 56safety measures, 60-61Saffir-Simpson category, 57tracking, 37wave height, 57wind activity, 57

Hurricane Elena, satellite image, 36-37Hurricane Georges, 4hurricane hunter P3 airplane, 71Hurricane Katrina, 58-59Hurricane Rita, satellite image, 62-63hydroelectric plant, 49hydrologic cycle, 20-21hydrometeor, 42hydrosphere, 8, 21hygrothermograph, 67

I-Kice, 9

polar, 5, 10, 84-85, 90ice core, paleoclimatology, 80, 81Intertropical Convergence Zone (ITCZ), 12, 28inversion fog, 45isobar, 13, 68isotherm, 69

meteorological station, 67, 70meteorology, 62-73methane, concentration, 80-81, 90minimum thermometer, 67mist, 44, 45monsoon, 19, 28-29, 30-31

areas affected, 28effects, 30-31formation in India, 28-29, 31intertropical influence, 28North America, 28

Moon, weather folklore, 65mountain, 24-25

Andes, 24-25barrier to wind and moisture, 9climatic effects, 24-25climatic zones, 79descending wind, 25high, 11major ranges, 25monsoons, 29uneven mountainside, 25vegetation, 25winds, 26

mythology and religion, 76-77Aztecs, 77Egyptians, 76Greeks, 76Hindus, 77Incas, 77Japanese, 77Mayans, 77Orient, 77pre-Columbians, 77Romans, 76-77

Nnimbostratus cloud, 39nitrogen, 10, 17noctilucent cloud, 11North America

El Niño, 35global warming, 90monsoons, 28potable water, 21tornadoes, 53, 54-55

Northern Hemisphere, 22, 28, 52, 56

Ooak tree, weather folklore, 64-65occluded front, 15, 68ocean

circulation, 9current: See ocean currentEl Niño, 32-33, 34-35hurricanes, 56level changes, 5, 32, 83. 85temperature distribution, 26-27, 29water return, 20weather data, 70

ocean current, 22-23changes, 84deep, 22, 23formation, 22-23gulf stream, 85Labrador, 85surface, 22

oceanographic ship, 70oxygen, 10, 17, 88ozone, 10, 11, 83, 88, 89ozone layer, 88-89

atmosphere, 11CFC gas, 88deterioration, 88global warming, 83thinning, 90weakening, 88-89

Ppaleoclimatology, 80-81

chronology, 80-81gas measurement, 80human activity, 81methane concentration, 81samples, 80, 81

permafrost, 9perspiration, 20pH, acid rain, 87 photochemical reaction, 87photosynthesis, 9, 82pinecone, weather folklore, 64plant

acid rain, 86flooding, 48hydrologic cycle, 20ozone layer, 89weather folklore, 64, 65

polar cell, 13polar ice

cap, 10melting, 5, 84-85, 90

polar mountainous climate, 79pollution, 11, 24

See also acid rainprecipitation

condensation, 8droplet formation, 20formation, 14, 21, 24, 40-43rain: See rainsleet, 42snow, 14, 25, 40, 42-43snowfall record, 42

pressurehigh, 12, 69low, 12, 13, 68

psychrometer, 67

Q-Rradar station, 71radiation

solar, 8, 9, 11, 16

jet-stream current, 12, 13Rossby wave, 14

katabatic wind, 26Köppen climate classification, 79

LLa Niña

conditions during, 33effects, 32, 35

Labrador current, 85lake, seasonal water circulation, 23land

temperature distribution, 26-27, 29weather data, 70

lenticular cloud, 39lightning, 46-47

electrical potential, 47origin, 46types, 46

lightning rod, 47lithosphere, 8, 9Lorenz, Edward, 5low pressure, 12, 13, 46, 56, 68

See also cyclonelow pressure trough, 69

Mmagnetosphere, 16, 17map, weather: See weather mapmaritime sounding probe, 71maximum thermometer, 67mercury barometer, 66mesosphere, 11meteor, 11meteorological aircraft, 71, 81meteorological buoy, 71meteorological shelter, 67

100 INDEX

ultraviolet, 7, 88, 89radiation fog, 45radiosonde, 70, 71rain, 18, 78

acid, 87causes, 14, 25climatic zones, 78flooding, 48formation, 40-41global warming, 82importance, 18-19measuring instruments, 67monsoons, 19, 28-29torrential, 19, 49toxic, 86-87typhoons, 19

rain gauge, 67rain meter, 67rainforest, 78religion: See mythology and religionrocket probe, 10Rossby wave, 14rotation, Earth, 12

Ssafety, hurricanes, 60-61Saffir-Simpson category, hurricanes, 56salt water (sea water), 21, 90satellite, 72-73

geostationary, 72infrared images, 71meteorology, 10, 37, 62-63, 70, 71military, 10mobile, 72-73polar orbit, 72

season, lake circulation variations, 23seaweed, weather folklore, 64shooting star, 11silicate soil, 87skin cancer, ozone layer weakening, 89sky, colors, 16-17

sleet, 42snail, weather folklore, 65snow, 14, 25, 40, 42-43snowfall, record annual, 42soil

acid rain consequences, 87calcareous, 87drought, 50field capacity, 51flooding effects, 48saturated, 50silicate, 87water, proportion of, 51wilting, 51

solar radiation, 8, 9, 16absorption, 11reflection, 11

solar wind, 16, 17sounding probe, launchable, 71South America

El Niño, 32-33, 35 global warming, 90potable water, 21

Southern Hemisphere, 22, 28, 52, 56stationary front, 15, 68stratocumulus cloud, 39stratosphere, 11stratus cloud, 38, 39subpolar arctic current, 23Sun, 9

cosmic ray, 11radiation, 8-9sunlight measurement, 66ultraviolet ray, 10-11volcanic eruption, 9

surface ocean current, 22swallow (bird), weather folklore, 64

Ttaiga, 25, 79temperate zone, 78

temperatureatmospheric dynamics, 12climate zones, 78differences over land and ocean, 26-27, 29earth, over the years, 82, 90global warming, 82-83greenhouse effect, 10measuring instruments, 67variation, 7

thermal expansion, 84thermal inversion, 11thermometer, types, 67thermosphere, 10thunder, 46tide, 22toad, weather folklore, 64topography, irregularities, 12tornado, 52-53

causes, 52damages, 5, 52, 54-55formation, 52Fujita-Pearson scale, 53, 54ten most devastating, 55United States, 54-55where and when, 53wind velocity, 53

toxic rain: See acid raintrade winds, 12, 32transpiration, 20Tri-State tornado (United States), 54-55tropical cyclone, 36-37

See also cyclone; hurricane; typhoontropical depression, 58tropical zone, 78troposphere, 11, 38tundra, 25, 79typhoon, 19, 36, 57

U-Vultraviolet radiation (UV radiation), 88, 89

CFC gas, 88

ozone, 7, 90types, 89

ultraviolet ray, 10-11valley, wind, 26velocity, wind

minimum/maximum, 13tornado, 52

visibility, fog, 44volcanic eruption, 9

Wwarm front, 14, 15, 68water, 7, 20-21

accumulation, 48-49acid rain consequences, 87availability, 21circulation, 9clouds, 39distribution worldwide, 21droplet formation, 20dry zones, 50evaporation measurement, 66gods and rituals, 76-77gaseous state, 20liquid state, 21ocean currents, 22-23return to ocean, 20runoff, 21scarcity, 50-51seasonal lake circulation, 23soil saturation, 50solid state, 21types, 20, 21underground circulation, 20-21

water cycle, 20-21water vapor, 10, 20weather aircraft, 71, 81weather folklore, 64-65

almanac forecast, 65clear sunset, 65clouds, 65

Moon, 65morning dew, 65signs from plants and animals, 64, 65weather prediction, 65wind, 65

weather forecast, 70-71acoustic signal, 70aerosonde pilotless weather aircraft, 71air, 70almanacs, 65artificial satellites, 71, 72-73autonomous underwater vehicle, 70better forecasts, 71data collection, 70factors affecting, 5hurricane hunter P3 airplane, 71land, 70launchable sounding probe, 71maritime sounding probe, 71meteorological aircraft, 71, 81meteorological buoy, 71meteorological centers, 71meteorological station, 70oceanographic ship, 70radar station, 71radiosonde, 70, 71sea, 70sources, 70

weather map, 68-69cold front, 14, 68history of, 68isobar, 68nomenclature, 68overcast sky, 69symbols, 68upper-air, 69upper-level, 69warm front, 14, 68wind velocity, 69winds, 69

weather prediction, 4-5anemometer, 67artificial satellites, 72-73barograph, 66barometers, 66

data recorder, 67evaporimeter, 66 heliophanograph, 66hygrothermograph, 67information compilation, 66-67meteorological shelter, 67psychrometer, 67rain gauge, 67rain meter, 67thermometers, 67weather folklore, 64-65weather maps, 68-69weather stations, 67weather vane, 67workplace, 66-67

weather station, 67weather systems analysis, 13weather vane, 67wet-bulb thermometer, 67whirlwind, 26wilting, water scarcity, 51wind, 7, 8

coastal breeze, 26, 27cold fronts, 14continentality effect, 27direction, 13hurricane, 57measuring instruments, 67monsoon: See monsoonmountains, 24-25, 26ocean currents, 22solar: See solar windtides, 22tornado: See tornadotrade, 12, 32types, 26valleys, 26velocity, 13, 69weather maps, 69whirlwind, 26

World Meteorological Organization, 70


Bisl 04 weather and climate

Education

Transcript of Bisl 04 weather and climate