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Published byAudrey Cannon Modified over 9 years ago
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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
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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)
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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
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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
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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
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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!!!
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ITCZ in July ITCZ in January
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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
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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
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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
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Key Figures 10.2, 10.9, 10.11, 10.15, 10.16, 10.19, 10.33, 10.40, 10.41, 10.45
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