1. CIRCULATION OF THE ATMOSPHERE
Chapter 7
CIRCULATION OF THE ATMOSPHERE

2. Atmospheric Circulation
Atmospheric circulation depends on the scale at which you examine it:
Macroscale
Planetary scale
Synoptic scale
Mesoscale
Microscale

3. Hadley Cell One of first attempts to characterize circulation
A thermal air flow representation
--- a non-rotating Earth
--- a single convective cell
Equator-to-Poles
--- circulation the product of differential heating

4. Idealized Model
- Because of Coriolis Effect model winds do not flow in a north-south direction
- There exists a planetary wind system that develops in response to planetary pressure patterns and modified by Coriolis

5. Idealized Model, cont
Earth generalizes seven pressure “belts” of expanding and subsiding air centered on the Equator
Belts of pressure give rise to three alternating pressure winds per hemisphere
*remember that pressure is relative*

6. Idealized Model, cont
Two belts of divergent flow out of the Polar Highs flow Equator- ward. CF “bends” air flow to create Polar Easterlies
Remaining four wind belts are associated with divergent flows from the Subtropical Highs
--- centered at about 30o N&S, zones of subsiding and divergent air

7. Idealized Model, cont
--- CF makes flow here nearly west-to-east – Prevailing Westerlies
--- air flow splits here, some returns Equator-ward as the Trade Winds
(returns to the Inter-tropical Convergence Zone),
remainder convectively lifted over cooler polar air

8. Special Winds Jet Stream One of several planetary air flows
--- best known is the Polar Front Jet Stream
Brought about by temperature gradient
S.-to-N.
--- contrast produces large difference between H and L pressure systems
--- meandering helps to separate and define Polar and Prevailing Westerly air flow / cP and mT air mass areas

9. Special Winds Monsoon From Arabic “mausim” seasonal wind
A synoptic air flow / there are two and they are seasonal
--- winter – eastern Asia; continental and very high pressure; dominates N.H. Winter; affects flow of the Jet Stream
--- summer- south Asia; marine and low pressure; origins more complex than winter monsoon… migration of ITC /
el nino development altered or altering (?)

10. Local Winds
Small scale winds produced by localized pressure gradient differences
--- may be time sensitive
(1) land-sea breeze
(2) mountain-valley breeze

11. Special Local Winds Katabatic Winds
Product of the motion of intensely cold air from highland regions
Gravity flow so mountain affected
Best developed over Greenland and Antarctica

12. Special Local Winds, cont
Chinook
Low pressure, leeward sides of mountains
PGF pulls air over mountain
--- adiabatic cooling than rapid adiabatic heating
(helped by air dry-ness)
Often dramatic effect on leeward mountain slope temperature