Circulation in the Atmosphere
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Circulation in the Atmosphere. Circulation in the atmosphere. Balance of forces in the fluid motion. Forces due to planetary rotation Centrifugal force  Geoid Coriolis force  Deflection of moving fluid Pressure gradient force From high to low pressure.

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Circulation in the atmosphere

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Circulation in the Atmosphere

Circulation in

the atmosphere


Balance of forces in the fluid motion

  • Forces due to planetary rotation

    • Centrifugal force  Geoid

    • Coriolis force  Deflection of moving fluid

  • Pressure gradient force

    • From high to low pressure


Deflection of air flow due to Coriolis force

Low Pressure

_

Surfaces of

constant pressure

y (latitude)

x (longitude)

+

High Pressure


Balanced flow: geostrophic balance

Fpressure

Low Pressure

High Pressure

FCoriolis

  • Coriolis force 90 degrees to the right

  • Pressure force down the gradient

  • Air flows along the line of constant pressure

  • Particles will have the high pressure on their right (opposite in the southern hemisphere)


Geostrophic circulation

  • What would be the direction of (1) the pressure force and (2) the Coriolis force in geostrophic balance?

  • What would be the direction of geostrophic flow?

L

H

Cyclonic

Anti-cyclonic


Geostrophic circulation

Now we are in the Southern Hemisphere, what would be the direction of the geostrophic flow?

L

H

Cyclonic

Anti-cyclonic


Tropical cyclone: an intense low pressure system

H

H

L

H

H

Air circulates around the low pressure


Flow under radial pressure gradient

  • A bucket full of water

  • Open up a hole in the middle

    • Generates a low pressure

  • What would happen to the water?

    • Non-rotating

    • Rotating


Tropical cyclones

  • Coriolis effect

  • Air flows around the low pressure

  • counter-clockwise

Energy source

Warm, moist air from tropical ocean


Storm surge

Graphic illustration by National Hurricane Center

http://www.nhc.noaa.gov/surge/animations/hurricane_stormsurge.swf


Atmosphere-ocean interaction

What are the ways that the Earth’s atmosphere and ocean interact?


Wind-driven ocean currents

  • Atmospheric winds applies frictional force on the surface waters

  •  Ocean waves

  • Wind-driven circulation

    • (next week)


Water cycle

Implications to the salinity of seawater?


Temperature

ITCZ

Warm SST, low SSS

Excess precipitation

Salinity

Subtropics

Warm SST, high SSS

Excess evaporation

Sea surface temperature and salinity are controlled by air-sea interaction


4 components of air-sea heat flux

  • Incoming shortwave radiation

    • Latitudes, cloud cover

  • Outgoing longwave radiation

    • Temperature, water vapor, cloud cover

  • Sensible heat flux

    • Boundary layer turbulence

  • Latent heat flux

    • Evaporation


Shortwave radiation

  • Climatology

    • Average over long time period (1968-1996)

    • Upward positive (positive into the atmosphere)


Factors controlling SW radiation

  • Latitude

  • Cloudines (albedo)


Longwave radiation

  • Climatology (1968-1996)

    • Upward positive (positive into the atmosphere)


Longwave radiation

  • SST, cloud and water vapor


Sensible heat flux

  • Climatology (1968-1996)

    • Upward positive (positive into the atmosphere)

    • Turbulent heat exchange between ocean and atmosphere


  • Driven by surface wind speed and air-sea temperature difference

Sensible heat flux


Latent heat flux

  • Climatology (1968-1996)

    • Upward positive (positive into the atmosphere)

    • Proportional to the rate of evaporation


  • Rate of evaporation

    • - Wind speed and relative humidity

Latent heat flux


Net heat flux

  • Climatology (1968-1996)

    • Upward positive (positive into the atmosphere)


Ocean heat transport

  • Ocean gains heat from the atmosphere in tropics

  • Ocean circulation transports heat poleward, and release back to the atmosphere at high latitudes


Biogeochemical cycle

(in October after midterm)


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