Post on 12-Jan-2016
Ch. 7 and Supplement Ch. 7 and Supplement 77
Weather and Climate Weather and Climate
Adapted from Ms. Sealy’s ppt
Weather– The short-term day-to-
day changes in temperature, air pressure, humidity, precipitation, sunshine, cloud cover and wind direction and speed.
– Most weather is predicted using:
weather balloons, aircraft, radar, and satellites
Climate– is the long term average precipitation
and temperature of an area– is determined by air pressure,
albedo, angle of sunlight, clouds, distance to oceans, fronts, heat (convection), land changes, latitude, location, humidity, mountain ranges, pollution, rotation, wind patterns and human
– Climate is what you expect, weather is what you get!
Climate
the average weather patterns for an area overa long period of time (30 - 1,000,000 years).
is
It is determined by
Average Precipitation Average Temperatureand
which are influenced by
latitude altitude ocean currents
and affects
where people live how people livewhat they
grow and eat
Fig. 6.3, p. 123
• Shows the precipitation and temperature on one graph. Easy to compare biomes
Climatograms
• KEY PROPERTIES OF AIRKEY PROPERTIES OF AIR– Cold air is more dense than warm
air– Cold air sinks and warms– Warm air rises and cools– Warm air can hold more water vapor
than cold air– As air cools, it cannot hold as much
water vapor, so it may precipitate
ATMOSPHERIC CIRCULATION PATTERNS
Weather Changes• Air Mass: a large body of air that has
similar temperature and moisture level throughout.
• Air Masses that affect the US are cA, cP, mP, mT and cT
When air masses meet, the boundary between them is called a front and it causes changes in weather
• Cold front: when a cold air mass collides with a stationary warm air mass. The result is: thunderstorms, short bursts of heavy rain
Warm Front:
• when a warm air mass collides with a stationary cold air mass. The result is: warm steady rain
Air PressureAtmospheric pressure is highest near
Earth’s surface due to weight of air above.
Plotting areas of same pressure (isobars, usually measured in mm Hg) shows high and low pressure areas.
High and Low Pressure
High pressure = cold, dense air, descends toward surface; usually means fair weather.
Low pressure = warm, less dense air; rises, expands then cools; often cloudy, stormy. If there’s enough water and condensation nuclei present, rain results.
Weather is also affected by changes in atmospheric pressure
• High pressure has descending air that moves outward from the center of the high-pressure system. Descending air is warm and dry. The result is: nice dry weather
Low pressure• has ascending air that flows
towards the center of the low-pressure area. Ascending air-cools and condenses as it rises. The result is: clouds, rain
Energy Transfer by Convection in the Atmosphere
Convection Cell
Global Air currents affect regional climates
• Uneven heating of the Earth’s surface causes the equator to receive more sunlight making it hotter
• The poles receive less light making them cooler.
• This causes areas of high and low pressure and global circulation of winds as air moves from high to low pressure
Climate type
Cold
Cool Temperate
Warm Temperate
Tropical
(equator)
Tropical
Warm Temperate
Cool Temperate
Cold
Fig. 6.6a, p. 125
Fig. 6.6b, p. 125Initial pattern of air circulation
Deflections in the paths of air flownear the earth’s surface
30°S
Easterlies
Westerlies
Southeasttradewinds
(Doldrums)
Northeasttradewinds
Westerlies(from the west)
Easterlies(from the east)
60°S
equator
30°N
60°N
Seasons
• Seasonal changes in temp and precipitation affect climate because the earth is tilted on its axis. It is colder in the winter and warmer in the summer because:
• The earth is tilted 23.5° on its axis
Fall(sun aims directly at equator)
Summer(northern hemisphere
tilts toward sun)
Spring(sun aims directly
at equator)
23.5 °Winter(northern hemispheretilts away from sun)
Solarradiation
Fig. 6.5, p. 124
Coriolis Effect• Rotation of
the Earth on its axis prevents air currents from moving directly north or south causing the winds to curve
• http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm
http://www.science-house.org/nesdis/upwelling/background.html
Albedo
• Is the reflectivity of a surface to solar radiation.
• Snow= high albedo (0.8)
• Water= low (0.07)
• Forest = .05-0.1
• Average albedo of the earth is 0.37
Altitude
• For every 1000 feet, there is a 3°F drop in temperature.
• Every 300 feet in elevation is equivalent to a shift of 62 miles north in latitude and biome similarity.
CLOUDS
Ocean currents
• Surface currentsSurface currents– Driven by wind (10%)
• Deep water currentsDeep water currents– Driven by density and gravity
Influenced by
• Solar heating-
• Winds
• Gravity
• Coriolis
• http://www.montereyinstitute.org/noaa/lesson08.html
• http://www.montereyinstitute.org/noaa/lesson08/l8la1.htm view at home
Polar (ice)
Subarctic (snow)
Cool temperate
Warm temperate
Dry
Tropical
Highland
Major upwelling zones
Warm ocean current
Cold ocean current
River Fig. 6.4, p. 124
– Ocean Currents Affect climateOcean Currents Affect climate• Differences in water temp, winds and
the rotation of the earth create currents.
• Currents redistribute heat. For Currents redistribute heat. For exampleexample the Gulf Stream brings the Gulf Stream brings heat to Europe and moderates the heat to Europe and moderates the climate climate
• Water holds a lot of heat – has Water holds a lot of heat – has a high heat capacity. a high heat capacity.
• This means water takes a long This means water takes a long time to heat up and a long time time to heat up and a long time to cool offto cool off
• Oceans moderate climatesOceans moderate climates– Coastal areas have warmer winters
and cooler summers
OCEAN CIRCULATION PATTERNS
Cool airdescends
Land warmer thansea; breeze flowsonshore
Warm air ascends
Fig. 6.15a, p. 130
Water also changes climate by causing land breezes and sea breezes
Warm air ascends Land cooler than
sea; breeze flowsoffshore
Cool airdescends
Fig. 6.15b, p. 130
Upwelling
• Upwelling is created when the Upwelling is created when the trade winds blow offshore trade winds blow offshore pushing surface water away pushing surface water away from land. The outgoing from land. The outgoing surface water is replaced by surface water is replaced by nutrient bottom waternutrient bottom water
Wind
Movement ofsurface water
Diving birds
Nutrients
Upwelling
Fish
Zooplankton
Phytoplankton
Fig. 6.9, p. 126
The El Nino Southern Oscillation occurs every few years in the Pacific Ocean
– In an ENSO, prevailing westerly winds In an ENSO, prevailing westerly winds weaken or stopweaken or stop
– Surface waters along the coast of Surface waters along the coast of North America and South America North America and South America (west) become warmer(west) become warmer
– Normal upwelling stopsNormal upwelling stops– This reduces the population of some This reduces the population of some
fish speciesfish species– Also causes severe weather, storms in Also causes severe weather, storms in
the US especially CA, and drought in the US especially CA, and drought in southeast Asiasoutheast Asia
Normal Conditions
Cold water
Warm water
Thermocline
SOUTHAMERICA
Warm waterspushed westward
AUSTRALIA
EQUATOR
Surface windsblow westward
Fig. 6.10a, p. 127
El Niño Conditions
Cold water
Thermocline
Warm waterWarm water deepens offSouth America
SOUTHAMERICA
Warm waterflow stoppedor reversed
AUSTRALIA
EQUATOR
Drought inAustralia andSoutheast Asia
Winds weaken,causing updraftsand storms
Fig. 6.10b, p. 127
El Niño
Unusually warm periods
Unusually high rainfall
Drought
Fig. 6.11, p. 127
La Nina• La Ninas follow an El Nino and
are characterized by cooling trends. La Nina brings more Atlantic hurricanes, colder winters in the north and warmer winters in the south.
• Can lead to wetter winters in the Pacific NW, torrential rains in SE Asia, lower wheat yields in Argentina and more wildfires in Fla.
The chemical makeup of the atmosphere affects the weather.
Small amounts of water vapor, carbon dioxide, ozone, methane, nitrous oxide and chlorofluorocarbons trap heat in the atmosphere warming the planet. These gases are called: greenhouse gases
• The greenhouse effect is when greenhouse gases allow light, infrared radiation and UV radiation through to the surface of the earth where it is reflected back into space. The greenhouse gases trap some reflected infrared radiation
Rays of sunlight penetrate the lower atmosphere and warm the earth's surface.
The earth's surface absorbs much of the incoming solar radiation and degrades it to longer-wavelength infrared radiation (heat), which rises into the lower atmosphere. Some of this heat escapes into space and some is absorbed by molecules of greenhouse gases and emitted as infrared radiation, which warms the lower atmosphere.
As concentrations of greenhouse gases rise, their molecules absorb and emit more infrared radiation, which adds more heat to the lower atmosphere.
(a) (b) (c)
Fig. 6.13, p. 128
Topography of the earth also creates microclimates
A microclimate is small area that has a different climate than the general climate of an area.– Vegetation in an area influences climate:
forests stay warmer in the winter and cooler in the summer because of the trees
– Cities create heat islands that trap heat and decrease wind
speeds
• Mountains Affect Precipitation• Air rises, cool and rains• Air descends, warms and draws up moisture• This creates a
rain shadow effect where one side
of the mountain
receives most of
the rain and the
other side is very dry
LOCAL GEOGRAPHY
a Winds carrymoisture inland
from Pacific Ocean
b Clouds, rain onwindward side ofmountain range
c Rain shadow onleeward side ofmountain range
Moist habitats 15/25
1,000/85 1,800/125
3,000/854,000/75
1,000/252,000/25
Fig. 6.14, p. 129
The rain shadow effect changes climate
Mojave Desert is in the rain shadow of the Sierra Nevada Mts.
Weather Extremes– Hurricanes: most severe of all
• What is it? Tropical storm with winds greater than 75 mph
• The bad: loss of life and property
• The good: flushes out coastline
• Hurricane Katrina- August 2005
• The most destructive hurricane (economically ) ever. Landed in Louisiana as a category 3
• $75 billion and 1,830 deaths
• 1900 Galveston Hurricane 6,000-12,000 died
Tornadoes:• Form when cold dry air collides
with warm moist air, which causes the warm air to rise quickly making a funnel cloud
• Winds up to 300 mph
• Classified as F1-F6 (Fujita)
• Most common in US
• Usually occur between April-July and often in the center of the country (Tornado Alley)
Risk of Tornadoes
Highest
High
Medium
Low
Hurricane Frequency
High
Moderately high
Gulf of Alaska
Prince Williams Sound
CANADA
UNITED STATES
Grand Banks
Atlantic OceanMEXICO
Fig. 6.2, p. 122
• Deforestation
• Urbanization
• Release of pollutants
• Burning of fossil fuels
HOW DO HUMANS AFFECT CLIMATE?