Lecture 11. Local Circulations IILand/Sea Breeze - A Thermally Driven Circulation• In colder air, pressure drops faster with height• Air moves around circulation in a couple of hours, so Coriolis deflection not too important.The Florida Sea Breeze• During most summer days, Florida’s weather consists of afternoon thunderstorms over the warm la...• At night, thunderstorms develop over the ocean just offshore of the land breeze.Mountain/Valley Circulations• Day: Air near slopes warms, risesPressure surfaces further apart where air warm, less denseHorizontal pressure gradient pulls air toward mountain during day.• Night: Air near slopes cools, sinksMonsoons• Winds reverse direction seasonally as tropical continents become warmer, then colder than nearb...• Most pronounced over SE Asia; also occurs over Mexico and SW US deserts, and N Australia• Like a giant land/sea breezeSummer: Low pressure over hot landMoist air flows from ocean to land,then rises, making heavy rain.Winter: High pressure over cold landDry air flows from out from land,and rain now mainly over oceanThe SE Asian MonsoonCherrapunji -- 425 in of rain annually, mostly in July and AugustLecture 11. Local Circulations IILand/Sea Breeze - A Thermally Driven Circulation• In colder air, pressure dropsfaster with height• Air moves around circulationin a couple of hours, so Corio-lis deflection not too impor-tant.PGFPGF50 km1-2 kmCFCFEOM7.4The Florida Sea Breeze• Duringmostsummerdays, Florida’sweather consists ofafternoon thunder-storms over thewarm land, whichfirst develop at theinland edge of thesea-breeze• At night, thunder-storms develop overthe ocean just off-shore of the landbreeze.Sea Breeze FrontSinking air,no cloudsover oceanRising air,thunderstormsat inland edgeof sea breezeSun-warmed landMountain/Valley Circulations• Day: Air near slopes warms, risesPressure surfaces further apart where air warm, less denseHorizontal pressure gradient pulls air toward mountain during day.• Night: Air near slopes cools, sinksEOMMonsoons• Winds reverse direction seasonally as tropicalcontinents become warmer, then colder thannearby ocean:• Most pronounced over SE Asia; also occurs overMexico and SW US deserts, and N Australia• Like a giant land/sea breezeSummer: Low pressure over hot landMoist air flows from ocean to land,then rises, making heavy rain.Winter: High pressure over cold landDry air flows from out from land,and rain now mainly over oceanThe SE AsianMonsoonCherrapunji -- 425 inof rain annually,mostly in July
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