1Lecture Ch. 8a• Review of Ch.7 Concepts– Homework Ch. 7, Prob. 3• Cloud Classification• Precipitation ProcessesCurry and Webster, Ch. 8Please complete online evaluations!Atmospheric Structure• !Structure of the atmosphere– Decreasing temperature with altitude– Decreasing pressure with altitude– Changes in water vapor with altitude• Temperatures in meteorology– Potential temperature (meteorologists’entropy)– Virtual (potential) temperature– Equivalent (potential) temperature• Describing the atmosphericstructure– Example: Skew-T log P plot– Example: TephigramInversions• Inversion: A condition of strong stabilitycharacterized by a positive temperaturegradient.2Subsidence Inversions• Subsidence Inversion– Cause: adiabatic compression and warming of alarge layer of earth as it sinks to lower altitude.• dT/dP = 1/ (Cp ρ) , where Cp is essentially constantover T.Radiation Inversions• Radiation InversionCause:• radiation of heat by the ground at night• air adjacent to the the surface has a T < layer athigher elevationsWater Vapor in the Atmosphere• the Earth’s surface is the primary source of water vapor for the atmosphere• the amount of water vapor in the atmosphere depends on– (1) the amount which enters the atmosphere through evaporation and sublimation,– (2) its transport by motions of various scales throughout the troposphere and the lower stratosphere,– (3) the amount which leaves the atmosphere intermittently as rain, hail and snow• wv,sat, the amount of water vapor in air at saturation on a mass-per-mass basis, decreases with decreasingtemperature– the amount of water in an air parcel consequently decreases with altitude, reaching a minimum in the lowerstratosphere a few kilometers above the tropopause– stratosphere has very low water content• clouds and fogs form by cooling of moist air– cloud formation is driven by the rise of moist air due to thermally-driven updrafts, which result in simultaneouscooling and expansion; in many cases this expansion is close to adiabatic– fog formation and some stratus cloud formation can occur by isobaric cooling, caused by surface cooling– after a sufficient amount of cooling wv=wv,sat and a liquid condensate is formed; this process occurs when the dew-point temperature (Td) is reachedLifting Condensation Level• Liftingcondensation levelvaries with initialrelative humidityand is a weakfunction of initialtemperature10.1Seinfeld and Pandis, Fig. 15.113Cloud ClassificationCumulus CloudsSwelling CumulusActive heaped-up cloudwith flat bottom andgrowing cauliflower top.[http://www.fox8wghp.com/spacious.htm]10.2Cumulonimbus CloudsCumulonimbusMassive cloud systemproducing heavy showers,sometimes with hail. Mostactive clouds may havelightning and thunder. Afew spawn tornadoes.[http://www.fox8wghp.com/spacious.htm]10.2Stratus CloudsStratusLow lying layer of cloud(called fog if on theground) with no structure.[http://www.fox8wghp.com/spacious.htm]10.2Cirrus CloudsCirrus An ice crystal cloud, wispyin appearance. Mayproduce ice crystal snow inwinter or in mountains.[http://www.fox8wghp.com/spacious.htm]Altostratus CloudsAltostratusThickly layered waterdroplet cloud. Sun seen asthrough ground glass.[http://www.fox8wghp.com/spacious.htm]4Nimbostratus CloudsNimbostratusThick layered cloud -usually dark gray.Produces continuous rainor snow over large area.[http://www.fox8wghp.com/spacious.htm]FogGlobal Cloud Distribution• Zonallyaveragedclimatologyof cloud typeCloud Types and Drop Sizes• Frequencydistributions of themean cloud dropletsize for variouscloud typesPrecipitation Processes• Warm clouds (liquid water droplets only)• Cold clouds (ice
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