Post on 05-Jan-2016
description
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
x (longitude)
y (latitude)
+
_
Surfaces ofconstant pressure
Deflection of air flow due to Coriolis force
p
y
High Pressure
Low Pressure
Fpressure
FCoriolis
1) Coriolis force 90 degrees to the right2) Pressure force down the gradient3) Air flows along the line of constant pressure4) Particles will have the high pressure on their right
(opposite in the southern hemisphere)
Balanced flow: geostrophic balance
High Pressure
Low Pressure
H
L
• 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?
Geostrophic circulation
Cyclonic Anti-cyclonic
Geostrophic circulation
H
L
Now we are in the Southern Hemisphere, what would be the direction of the geostrophic flow?
Cyclonic Anti-cyclonic
Tropical cyclone: an intense low pressure system
L
H H
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
Energy sourceWarm, moist air from tropical ocean
Coriolis effectAir flows around the low pressurecounter-clockwise
http://www.nhc.noaa.gov/surge/animations/hurricane_stormsurge.swf
Storm surge
Graphic illustration by National Hurricane Center
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
Salinity
Sea surface temperature and salinity are controlled by air-sea interaction
ITCZ Warm SST, low SSS Excess precipitation
SubtropicsWarm SST, high SSSExcess evaporation
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
Sensible heat flux• Driven by surface wind speed and air-sea temperature difference
Latent heat flux• Climatology (1968-1996)
– Upward positive (positive into the atmosphere)
– Proportional to the rate of evaporation
Latent heat flux• Rate of evaporation
- Wind speed and relative humidity
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)