Chapter 7

CIRCULATION OF THE ATMOSPHERE

Atmospheric Circulation

Atmospheric circulation depends on the scale at which you examine it:

Macroscale(1) Planetary scale (2) Synoptic scale MesoscaleMicroscale

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

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

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*

Idealized Model, cont

(1) Two belts of divergent flow out of the Polar Highs flow Equator-ward. CF “bends” air flow to create Polar Easterlies

(2) 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

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

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

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 (?)

Local Winds

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

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

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