第八章大气环流的长期变化1

全球气候系统GlobalClimateSystem第八章大气环流的长期变化第八章全球大气环流的长期变化8.1全球大气环流的平均状况

8.2大气活动中心与大气涛动8.3高空大气环流的变率8.4季风系统

大气基本概况ATMOSPHERICVERTICALSTRUCTUREThetroposphere(0-~10km) contains~80%oftheatmosphericmass.Temperaturesincreasewithaltitudeinthestratosphere(10-50km)duetoabsorptionofUVlightbyozone(O3).Thereislimitedexchangeofmaterialbetweenthetroposphereandthestratosphere.ATMOSPHERICPRESSUREAtmosphericpressuredecreasesrapidlywithheight.Climbingtoanaltitudeofonly5.5km,wherethepressureis500mb,wouldputyouaboveone-halfoftheatmosphere'smolecules.Example:T=15C=288Kr=1.2kg/m3R=[287.05JK-1kg-1][1J=1Nm]

p=1.013x105N/m2=1013mbIdealGasLawp=rRT大气环流DescendingAirHighPressureAscendingAirLowPressureDescendingAirHighPressureAscendingAirLowPressureTHERMALLY-DIRECTCIRCULATIONCOLDWARMTHERMALLYINDIRECTCIRCULATIONWARMCOLDEquatorNSHADLEYCELLISATHERMALLY-DIRECTCIRCULATIONTHERMALLY-DIRECTCIRCULATIONINANIDEALIZEDNON-ROTATINGEARTHTheprevailingcirculationoftheatmosphere030306060NSLatitudeHighHighLowLowSurfacePressureSystemsHADLEYCELLSARETHERMALLYDIRECTCIRCULATIONSFERRELCELLSARETHERMALLY-INDIRECTCIRCULATIONSAsare(weak)polarcellsLowPrecipitationoccursinbandsofsurfaceconvergence(lowpressureregions)030306060NSLowLatitudeHighHighLowLowAtmosphericVerticalCirculationSurfacePressureCenters030306060NSWesterlyEasterlySurfaceWinds2WVgsinf=-(1/r)Dp/DyGeostrophicBalance:Responsibleforeast-westcomponentofwindatsurfaceDp/Dy>0

Vg<0(easterlies)Dp/Dy<0

Vg>0(westerlies)Attheequatorthereareweakeasterlies(“doldrums”)全球平均环流JanuaryJulyNotetheseasonalchangesintheglobalatmosphericcirculationITCZmigrateswithSun,butlagsit...Seasonalchangesinupperair(500mblevel)atmosphericcirculationJanuar