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The General Circulation

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

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  1. 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

  2. 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)

  3. 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

  4. 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

  5. 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

  6. 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!!!

  7. ITCZ in July • ITCZ in January

  8. 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

  9. 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

  10. 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

  11. 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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