ATMOSPHERIC AND OCEANIC SCIENCES

OUTLINE1. Atmospheric Science

Atmospheric Gases around Planets of the Solar SystemVariation of Pressure and Temperature with AltitudeThe Residence Times of Water in the Atmosphere The Light SpectrumEnergy Balance in the AtmosphereAtmospheric CirculationThe Coriolis ForceCloudsPredicting and Forecasting the WeatherPrecipitation and Seasons

2. Oceanic ScienceOcean Temperature and SalinityAtmospheric Effects on OceansOcean CurrentsFish Productivity in OceansEl Nino/La NinaIce and GlaciersIce Evolution

3. Monitoring Satellites in Orbit

1 – Atmospheric Science

Atmospheric Gases around Planets of the

Solar System

- The atmosphere drives weather conditions.

- Gases are either retained or escape the atmosphere.

- The escape velocity is calculated from the energy balance equation of kinetic

energy = potential energy due to gravity.

- Kinetic energy = and Potential energy =

where m is the gas molecule mass, g is the gravity constant

and R is the planet’s radius. Vesc is the escape velocity.

- Thermal velocity of a gas molecule is due to its thermal motion

where T is the temperature and kB is the Boltzmann constant.

- A gas molecule escapes a planet’s atmosphere when

2

escmV)21( mgR

gR2Vesc =

mTk3V Bther =

escther V*10V

- Table 9-1: Estimation of the escape velocity for the planets of the solar

system

Planet

Temperature

(K)

Mass (kg) Radius (m) Gravity accel.

(m/s2)

Escape velocity

(km/s)

Mercury 701 3.18x1023 2.43x106 3.59 4.18

Venus 741 4.88x1024 6.06x106 8.87 10.37

Earth 288 5.98x1024 6.38x106 9.81 11.19

Mars 243 6.42x1023 3.37x106 3.77 5.04

Jupiter 165 1.90x1027 6.99x107 25.95 60.23

Saturn 133 5.68x1026 5.85x107 11.08 36.01

Uranus 78 8.68x1025 2.33x107 10.67 22.30

Neptune 71 1.03x1026 2.21x107 14.07 24.94

Pluto 41 1.40x1022 1.50x106 0.42 1.12

Table 9-2: Prediction of the ability for the planets of the solar system to retain some

gases. Planet

Escape

velocity

(km/s)

Molecular

velocity

for H2

(km/s)

Molecular

velocity

for O2

(km/s)

Molecular

velocity

for N2

(km/s)

Molecular

velocity

for H2O

(km/s)

Molecular

velocity

for CO2

(km/s)

Molecular

velocity

for CH4

(km/s)

Mercury 4.18 2.34

escapes

0.58

escapes

0.63

escapes

0.78

escapes

0.49

escapes

0.78

escapes

Venus 10.37 3.03

escapes

0.76

retained

0.81

retained

1.01

retained

0.63

retained

1.01

retained

Earth 11.19 1.89

escapes

0.47

retained

0.51

retained

0.63

retained

0.40

retained

0.63

retained

Mars 5.04 1.61

escapes

0.40

retained

0.43

retained

0.53

escapes

0.34

retained

0.53

escapes

Jupiter 60.23 1.43

retained

0.36

retained

0.38

retained

0.47

retained

0.30

retained

0.47

retained

Saturn 36.01 1.29

retained

0.32

retained

0.34

retained

0.43

retained

0.27

retained

0.43

retained

Uranus 22.30 0.99

retained

0.25

retained

0.26

retained

0.33

retained

0.21

retained

0.33

retained

Neptune 24.94 0.94

retained

0.23

retained

0.25

retained

0.31

retained

0.20

retained

0.31

retained

Table 9-3: Information about atmospheres around the planets of the solar system

Planet Retained gases

Mercury Thin atmosphere of sodium and potassium blown from the surface

Venus Mostly carbon dioxide (96%) with minor amounts of nitrogen (3.5%)

Earth Mostly nitrogen and oxygen. Minor amounts of carbon dioxide, ozone, argon

and helium. Water moisture (less than 4 %).

Mars Thin layer of mostly carbon dioxide, nitrogen, oxygen, argon

Jupiter Mainly helium (10%) and hydrogen (90%). trace amounts of water, ammonia,

methane, other carbon compounds

Saturn Thick atmosphere of mostly helium and hydrogen. Methane and ammonia are

also present

Uranus Mainly hydrogen (82.5%) and minor amounts of helium. Methane is present in

minor amount. Appears blue because of strong absorption of methane

Neptune Mainly hydrogen and helium. Also methane. Clouds made of crystals of

methane

Pluto Very thin atmosphere composed of carbon dioxide

Variation of Pressure and Temperature with

Altitude in Earth’s Atmosphere

Figure 9-1: Variation of the temperature with altitude around Earth

- Perfect gas law P*V = n*R*T

where P is the pressure and T is the

temperature

- Atmospheric pressure variation with

altitude

where Hs = 8.4 km.

- Airplane at 11 km altitude flies in

atmosphere with ¼ the ground level

pressure.

- Solar radiation hits the thermosphere.

- Ozone absorbs UV radiation in the

stratosphere.

)H/zexp(*)0(P)z(P s−=

-120

-100

-80

-60

-40

-20

0

20

40

0 50 100 150

Temperature vs Height

Tem

pe

ratu

re (

oC

)

Height (km)

Troposphere

Stratosphere

Mesosphere

Thermosphere

The Residence Time of Water in the

Atmosphere and in Oceans

- Water enters the atmosphere through evaporation from the oceans and leaves

it though precipitation.

- The water residence time is the average time that a water molecule remains in

the atmosphere.

- Residence time in the atmosphere = Total amount of water /Precipitation rate

= 2.5 cm equivalent moisture / 1 m per year

= 9 days.

- The residence time in the ocean = Total amount of water /Precipitation rate

= 5 km / 1 m per year

= 5,000 years.

- Water stays 5,000 years in the ocean, evaporates, stays 9 days in the

atmosphere before returning to the ocean.

Light Spectrum

10-6 mm 10-4 mm 10-2 mm 1 mm 102 mm 104 mm 106 mm

X rays

Vis = 0.4 to 0.7 microns

Infrared

Radar

Radio

UV

Wavelength

Figure 9-2: Wavelength ranges for the various electromagnetic radiations.

0

2

4

6

8

10

12

0 500 1000 1500 2000 2500

Po

wer

De

ns

ity (

10

13 w

att

s/m

3)

Wavelength (nm)

483 nm

visible

ultraviolet infrared

Figure 9-3: Spectral distribution of light emitted by the Sun

- Blue light is scattered

more than red light

(Rayleigh law).

- This is why the sky is

blue.

- If there were no

atmosphere, the sky would

be black.

- Scattering from cloud

droplets makes clouds

look white (Mie).

Light Spectrum

Energy Balance in the Atmosphere

Figure 9-4: Energy balance for Earth.

Solar radiation

warms half the globe

Earth radiates heat

in all directions

Equator

Tropic of Cancer

Tropic of Capricorn

rotation around Earth’s axis

23.5 o

- Solar radiation warms the Earth surface at an average of S = 1380 W/m2.

- The albedo is the fraction which is reflected back a = 0.33.

- The remaining amount (1-a)*S = 911 W/m2 is absorbed.

- Total absorbed solar radiation (1-a)*S*pR2 where R is the Earth radius. pR2 is the

area of a disk.

- Absorbed radiation is emitted back isotropically as infrared radiation following

the black body radiation law sT4*4pR2 where s is the Stephan-Boltzmann constant

and T is the surface temperature. pR2 is the area of the sphere.

- Balancing out what is absorbed and what is emitted yields:

- This corresponds to a predicted temperature of -21 oC. Much lower to the

measured temperature of +15 oC. Discrepancy is due to reabsorption by greenhouse

gases.

Energy Balance in the Atmosphere

K 2514σ

S*a)(1T

1/4

=

−=

Atmospheric Circulation

Heat transfer

radiation emitted by Earth

radiation received from the Sun

surplus

deficitdeficiteq

uat

or

nort

h p

ole

south

pole

Figure 9-5: Earth’s energy balance

- Differential heating generates

circulation and winds.

- Wind is produced when two

atmospheric layers meet.

- This generates closed-loop

circulation cells.

equator

north pole

south pole

rising warm air

descending cool air

rising warm air

descending cold dry air

Hadley Cell

Ferrel Cell

Polar Cell

easterlies

westerlies

Figure 9-6: Wind circulation currents around Earth

- Around the equatorial region is

a belt of rainforests with lots of

rain.

- Atmospheric circulation is the

major driving force for weather

producing events including

storms, precipitation,

development of hurricanes, etc.

Atmospheric Circulation

The Coriolis Force

Figure 9-7: Foucault pendulum veers slightly in the clockwise direction as it

swings back and forth at the Smithsonian institution in Washington DC

Figure 9-8: Two children throwing a ball on a spinning platform. In the moving

frame of the platform, the ball seems to veer to the right (clockwise) because by the

time the ball arrives, the second child would have moved.

- Two children riding on a circular platform

which is spinning counterclockwise.

- When one child tosses the ball to the other,

this one does not catch it because he would

have moved to the left by the time the ball

reaches him.

- A fixed observer would see the ball follow a

straight trajectory while the one throwing the

ball would see it move to the right (ball veers

clockwise).

The Coriolis Force

Figure 9-9: Cyclone (L) and anticyclone (H) regions on an isobaric map

showing the wind directions

Weather Map

- Earth’s rotation from west to east produces the Coriolis force which has

great effect on the weather.

- Isobaric maps contain equal-pressure contours.

- The pressure gradient force balances out the Coriolis force.

where r is the air density, U is the wind speed, W is the rate of rotation of

Earth and f is the latitude of the location on the globe.

- The wind speed can be estimated as :

- The wind direction is to the right of the pressure gradient (PG) force.

The Coriolis Force

)sin(U2PG fWr=

)sin(2PGU fWr=

wind direction

pressure gradient force

Coriolis force

Figure 9-10: Anticyclone (H) region on an isobaric map

- High (H) pressure region on a

weather map is referred to as

anticyclone.

- Anticyclone is associated

with clear skies.

- Anticyclone rotates clockwise

like the Foucault pendulum.

Weather Map

pressure gradient force

Coriolis force

wind direction

Figure 9-11: Cyclone (L) region on an isobaric map

- Low (L) pressure region is

referred to as cyclone on a

weather map.

- Cyclone is associated with

overcast sky and rain.

- Cyclone rotates counter

clockwise.

- A hurricane is a tropical

cyclone.

Weather Map

Figure 9-12: Eye of a hurricane seen from above in the northern

hemisphere

- A hurricane is a tropical

cyclone.

- Hurricanes rotate

counterclockwise in the

northern hemisphere.

- Hurricanes rotate clockwise

in the southern hemisphere.

- Hurricanes cannot cross the

equator.

- Hurricanes are called

typhoons in southeast Asia.

Hurricane

Clouds

Figure 9-13: Names of the various clouds. Latin words: cumulus (pile),

stratus (layer), cirrus (curl of hair), nimbus (rain).

cumulonimbus

cirrocumulus

cirrostratus

altostratus

nimbostratus stratocumulus

stratus

cumulus

altocumulus

cirrusblue sky

Predicting and Forecasting Weather

warm front moving north east

cold front moving south east

isobarslow-pressure cyclone

high-pressure anticyclone

Figure 9-14: Isobaric weather contour maps showing low (L) and high (H) pressure regions.

Weather balloon launches are performed at noon and midnight GMT. National Weather

Service produces isobaric maps and Weather Channel produces weather forecasts.

pressure

gradient

force

colder temperatures warmer temperaturesL

Coriolis

force

pressure

gradient

force

Coriolis

forcewind

direction

Figure 9-15: Wind pattern around a low pressure region in the northern

hemisphere

Wind Pattern

Figure 9-16: Weather station constantly takes meteorological data and

transmits them. Doppler radar is used to observe the development of storm

patterns locally.

Weather Station

Precipitation and Seasons

Figure 9-17: Total precipitation map for the US taken. Local and global

precipitation maps are produced on a regular basis using Doppler radars.

- Atmospheric circulation

controls the weather and

storms control precipitation.

- Oceans are deep and can

store heat while the

continental crust is thin; its

temperature varies wildly.

0

1

2

3

4

5

6

7

8

-80 -40 0 40 80

DecemberJune

Pre

cip

ita

tio

n (

mm

/day

)

Latitude (degrees)

Equator

90o S 90

o N

Figure 9-18: Variation of the mean precipitation averaged over many years with

latitude for the months of June and December.

Precipitation

June

December

Figure 9-19: Evolution of the Inter-Tropical Convergence Zone (maximum

precipitation) around the globe for the months of June and December.

ITCZ

2 – Oceanic Science

Ocean Temperature and Salinity

- Oceans occupy some 70 % of Earth’s surface.

- Top ocean surface temperature is around 25 oC.

- Drops to 1 oC at 5 km depth (abyssal plains).

- When the surface temperature rises above 28 oC, hurricanes form.

- The ocean water salinity (3.5 %) does not change much with depth.

- Salts come from dissolved rocks on continents (weathering) that get

carried down rivers to oceans.

- Rain tends to dilute salt water close to river deltas.

Atmospheric Effects on Oceans

- Three factors affect atmospheric effects on the ocean:

(1) heat exchange atmosphere/ocean

(2) precipitation and evaporation

(3) wind stress on the ocean surface

- Wind applies a force on ocean surface due to Earth’s rotation (Coriolis force).

- Wind causes a surface current to the right of the wind stress force (just like

the Foucault pendulum).

- The Coriolis force produces clockwise ocean currents (gyres) in the north.

wind stress Erkman force

Earth rotation Coriolis force

ocean current direction

Figure 10-1: The wind stress and the Coriolis forces equilibrate to produce an

ocean current.

intermediate water

equator south polenorth pole

surface

AABW

NADW

Figure 10-2: Atlantic Ocean thermohaline circulation showing the cold

Antarctic Atlantic Bottom Water (AABW) and the warmer North Atlantic

Deep Water (NADW) currents.

Ocean CurrentsThere are many global ocean currents (thermohalines) like:

The Antarctic Atlantic Bottom Water (AABW) is a cold current (4 km depth)

that runs north-south. Its temperature is between 1 and 2 oC.

The North Atlantic Deep Water (NADW) is another current that runs in the

opposite direction. Its temperature is between 2 and 4 oC.

Figure 10-3: The Mediterranean Sea/Atlantic Ocean thermohaline current.

- The Mediterranean Sea and Atlantic Ocean have slightly different salinity.

- There is more evaporation in the Mediterranean Sea.

- Mediterranean Sea water sinks under the Atlantic Sea water at Gibraltar.

Ocean Currents

Mediterranean Sea water

Atlantic Ocean water

water surface

Ocean Currents

Gulf Stream

Warm Current Ambient Current Cold Current

Labrador

Figure 10-4: Ocean currents (called gyres) around the globe circulate clockwise

in the northern hemisphere and counterclockwise in the southern hemisphere

Ocean currents:

- North Atlantic

- South Atlantic

- North Pacific

- South Pacific

- Indian Ocean

Ocean currents

travel at a few

km/hour.

Foucault Pendulum Anticyclone (H)

weather formationOcean current (gyre)

Gulf Stream

Figure 10-5: Summary of the Coriolis effects that spin in the clockwise

direction in the northern hemisphere

Coriolis Force

Fish Productivity in Oceans

- Light is absorbed in the upper 100 m layer of the ocean.

The rest of the ocean depth (5 km) remains dark.

- Fish lives in the top part where they can feed on phytoplankton.

- Every organic matter that dies falls to the bottom. The bottom of the ocean

where no fish lives is rich in these carbon-rich nutrients.

- Mixing of ocean water (up and down) favors fish productivity. This happens in

equatorial and high latitude regions.

- Coastal regions where river flow mixes with ocean water are also favorable for

fishing.

La Nina

- The El Nino and La Nina are distinct states of the ocean/atmosphere.

- They alternate along the equatorial line in the Pacific Ocean.

- The La Nina is the normal state

- There is plenty of fish off the coast of South America during La Nina.

Figure 10-6: Ocean currents during the La Nina state. The thermocline is

drawn in red.

South

America

Pacific OceanAsia

Atmosphere

LH20 oC

30 oC

El Nino- The El Nino is the opposite state. Ocean currents are inverted.

- There is no fish off the coast of Peru/Ecuador since there is no current that

brings carbon-rich nutrients from the bottom to the top.

- The El Nino tends to occur around Christmas (El Nino means The Child).

- El Nino can be felt worldwide (monsoon in India, drought in Ethiopia, etc).

Figure 10-6: Ocean currents during the La Nina state. The thermocline is

drawn in red.

20 oC

South

America

Pacific OceanAsia

Atmosphere

H L30 oC

Ice and Glaciers

- Ice plays a major role in Earth’s climate.

- Ice glaciers descend down mountains slowly carving the terrain.

- When they reach the ocean, they become icebergs that float till they melt.

- Most of the iceberg mass is submerged.

- Permanent ice sheets in the Arctic Ocean (Greenland) and Antarctica.

- The Greenland ice sheet is some 1 km thick. It’s been melting due to global

warming.

Ice Evolution

Glacial Striations

Figure 10-8: Striations left over by glaciers on bedrock

- Evolving glaciers leaves clues

on the terrain.

- One can infer the melting of

glaciers during previous

glaciation periods.

Laurentide Ice Sheet

Greenland Ice Sheet

Figure 10-9: Traces of receding glaciers after the last glaciation over the

northern part of North America. Arrows indicate the local directions of ice flow.

- The path of receding ice after

the last glaciation period have

been deduced.

Retreating Ice

3 – Monitoring Satellites in Orbit

Figure 11-1: - The AQUA satellite.

- The AQUA satellite orbits the

poles and monitors ocean

temperature, evaporation and the

hydrologic cycle.

- It detects IR radiation and

produces temperature maps.

- It can detect ocean temperature

anomalies during events like El

Nino.

Satellites

Figure 11-2: The CALIPSO satellite.

- The CALIPSO satellite helps

monitor clouds and aerosols and

their effect on air pollution.

- The AURA satellite studies the

ozone content in the atmosphere

and its depletion at the poles.

- GLORY studies aerosols and

their long term effect on climate.

- The TERRA satellite observes

the atmosphere, land and oceans

and their interactions.

Satellites

Figure 11-3: The GRACE satellite pair monitors the thickness of the ice sheets

- The two GRACE satellites

evolve in tandem to precisely

measure thickness of the polar ice

sheets.

- This is done by measuring

minute changes in Earth’s

gravitational field close to the

poles.

- The Greenland ice sheet is

receding fast.

Satellites

SummaryPlanet Earth

- Contains the right gases to sustain life.

- Has an atmosphere that shields it from dangerous solar radiation.

- Presence of water in oceans and much needed rain

- The water residence time is 5,000 years in the ocean and 9 days in the

atmosphere.

Earth’s Rotation and its Tilt Around its Axis

- Produces seasons.

- Drives atmospheric and ocean currents.

- Distribution of the Sun’s energy produces the weather.

- Storms can be predicted.

- Events like El Nino are understood.

- Weather monitoring satellites help.