The General Circulation  The large-scale wind patterns of the earth  Mission: to mitigate global temperature contrasts (decrease temperature gradients, redistribute warm and cold air across the globe)  Caused by the unequal heating of the earth’s surface

The General Circulation (High Latitudes)  “Polar Cell” = sinking/descending air at highest latitudes  Purpose is to bring warm air poleward (aloft) and cool air equatorward (below)  Atmospheric “Dump” –Mid-Latitude pollution carried there –Very stable troposphere, on average, so there is little mixing and a build-up of pollutants –Nearly permanent high pressure, sinking air, lead to very little precipitation (which would help clean the air)

The General Circulation (Tropics)  The Hadley Cell: large convection cell where air rises near the equator and sinks near 30 degrees north and south latitude  Purpose is to bring warm air poleward (aloft) and cool air equatorward (below) –Trade winds –Eckman transport (ocean) –ITCZ –Subtropical jet stream –Subtropical highs

G.C.: Hadley Cell: Trade Winds  Fairly constant tropical winds that transport air equatorward –Blow from the NE in the northern hemisphere –Blow from the SE in the southern hemisphere

G.C.: Hadley Cell: Eckman Transport  Vast stores of oceanic heat are distributed through this process  Upwelling: bring cold water up, heat it and send it poleward

G.C.: Hadley Cell: ITCZ  Where NE and SE trade winds meet  Convergence into belt of weak low pressure  Ascending branch of the Hadley Cell  NOT a straight line at the equator –Unequal heating of land and water –Follows the sun –Monsoon: seasonal reversal of wind direction  India, SW United States (wimpy one)  NOT a synonym for rain storm!!!

 ITCZ in July  ITCZ in January

G.C.: Hadley Cell: Subtropical Jet Stream  Farthest poleward (upper troposphere) part of Hadley Cell  Eastward momentum is transferred from tropics  Coriolis effect turns winds, resulting in a fast- moving ribbon of air generally moving west- to-east near 30 degrees latitude

G.C.: Hadley Cell: Subtropical Highs  Descending branch of Hadley Cell caused by upper tropospheric convergence  Very persistent  Convergence causes semi-permanent regions of surface high pressure –World’s deserts are found underneath and east –Horse Latitudes

El Nino El Nino  An irregular warming of the topmost layers of the eastern Pacific ocean –Generally occurs once every 3-7 years –Trade winds weaken  Upwelling of cold, nutrient-rich water off Peru ceases  Warm water sloshes eastward from western Pacific  Upwelling near equator weakens, water warms –Not fully understood –Teleconnections –NOT a weather event –La Nina

Key Figures  10.2, 10.9, 10.11, 10.15, 10.16, 10.19, 10.33, 10.40, 10.41, 10.45