CIRCULATION OF THE ATMOSPHERE Chapter 7 CIRCULATION OF THE ATMOSPHERE

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

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 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

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