Chapter Eleven Notes

Chapter Eleven Notes - Chapter Eleven Wind-Global Systems I...

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Chapter Eleven: Wind—Global 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 earth’s 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 earth’s 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
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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 Some surface air at 30 o  latitude moves back toward the equator Northeast trade: northern hemisphere, winds blow from northeast Southwest trade: southern hemisphere, winds blow from southeast Southeast and northeast trade converge as the intertropical convergence zone (ITCZ) and  continue d) Ferrel cell i) Thermally indirect cell ii) Westerlies Some air at subtropical high moves toward poles Deflected toward the east causing a westerly air flow Not constant, migrates areas of high and low pressure break up surface flow pattern from  time to time In middle latitudes of Southern hemisphere where surface is mostly water winds blow  more steadily from the west iii) Subpolar low As westerlies moves poleward is encounters cold air moving down from poles Two masses do not readily mix Separated by polar front (zone of low pressure, subpolar low) where surface air converges  and rises and storms develop iv) Some of the rising air at subpolar low returns at high levels to horse latitudes where it sinks  back to surface in vicinity of the subtropical high v) Completed when surface air from horse latitudes flows poleward toward the polar front e) Polar cell i) Polar easteries:  Cold air from poles is deflected by the coriolis force so general flow o air is  northeasterly ii) Along polar front a portion of rising air moves poleward and coriolis deflects the air into a  westerly wind at high levels iii) Air aloft reaches poles, sinks to surface and flow back towards the polar front
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  • Fall '05
  • Andresen
  • Atlantic Ocean, Pacific Ocean, Equator

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