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Unformatted text preview: Chapter Eleven: WindGlobal Systems I) General circulation of the atmosphere: when winds throughout the world are averaged for a long period and local wind patterns diminish A) Underlying cause is unequal heating of the earths surface B) Energy balance is not maintained for each latitude 1) Tropics experience a surplus of energy 2) Polar regions have net loss of energy C) Atmosphere transports warm air poleward and cold air equatorward to balance the inequities D) Two models: 1) Single-cell model a) Assumes that: i) The earths surface is uniformly covered with water ii) Sun is always directly over the equator iii) Ear does not rotate b) Huge thermally driven convection cell in each hemisphere c) Hadley cell: circulation of air i) Thermally direct cell because it is driven by energy from the sun as warm air rises and cold air sinks ii) Excessive heating of equatorial area produces broad region o low surface pressure while poles have region of high surface pressure iii) Cold surface polar air flows equatorward while at higher levels air flows toward the poles iv) Closed loop v) Rising air near equator and sinking air over poles vi) Excessive energy of tropics is transported as sensible and latent heat to poles d) Too simple does not take into account Coriolis and rotation 2) Three-cell model a) Assumes that: i) The earth is covered with water ii) Sun is always directly above the equator b) Three cells redistribute energy in each hemisphere c) Hadley cell i) Doldrums: over equatorial waters where the air is warm and horizontal pressure gradients are weak, and winds are light Warm air rises and sometimes condense into cumulus clouds and t-storms (convective hot towers) that liberate lots of latent heat Heat makes the air more buoyant and provides energy to drive the Hadley cell Rising air reaches tropopause which causes it to move laterally toward poles Coriolis deflects poleward flow toward right in Northern hemisphere and left in southern Creates westerly winds aloft ii) Subtropical highs As air moves poleward it cools by radiation and converges which increases the mass of air above the surface and causes air pressure at surface to increase around 30 o latitude At 30 o latitude convergence of air aloft produces belts of high pressure called subtropical highs As converging relatively dry air above highs descends and warms by compression Generally clear skies and warm surface temperatures Major deserts of world around here AKA horse latitudes because weak pressure gradients in center of high over ocean produces weak winds iii) Trade winds...
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This note was uploaded on 04/02/2008 for the course GEO 203 taught by Professor Andresen during the Fall '05 term at Michigan State University.
- Fall '05