upslopewinds演唱会

Ch10–LocalWindsCh10–LocalWindsIntroductionLocalwindsrefertoavarietyofmesoscalecirculationsotherthanthunderstorms.
Thesecirculationsfallintotwobroadcategories.
Thermallydrivenlocalwindsarecausedbylocaldifferencesinradiationalheatingorcooling.
Theyaremostnoticeablewhenlarge-scalewindsystemsareweakorabsent.
Externallydrivenlocalwindsareproducedwhenstrongwindsinteractwithlocalterrain(Lester,2006).
Ch10–LocalWindsIntroductionTheyaremostnoticeablewhenstrong,large-scalewindsystemsarepresent.
Thephenomenadiscussedunderthesecategoriesallhavethepotentialtoproduceimportantflighthazards.
Itisimperativeforyoutoknowwhattheircausesandcharacteristicsare,andhowtoidentifythemandavoidtheirworstconsequences(Lester,2006).
Ch10–LocalWindsIntroductionWhenyoucompletethischapter,youwillhavegainedthisknowledgeand,additionally,youwillhavecondenseditintosomeusefulconceptualmodelsofland,sea,mountain,andvalleybreezes;mountainwaves;anddownslopewinds(Lester,2006).
Ch10–LocalWindsSectionA–ThermallyDrivenLocalWindsSeaBreezeSeaBreezeFrontLandBreezeValleyBreezeMountainBreezeColdDownslopeWindsCh10–LocalWindsSectionB–ExternallyDrivenLocalWindsMountainLeeWavesTheLeeWaveSystemWarmDownslopeWindsMacroscaleWeatherPatternsCh10–LocalWindsLocalwinds–refertoavarietyofmesoscalecirculationsotherthanthunderstormsTheselocalwindcirculationsfallintotwobroadcategories:Thermallydrivenlocalwinds–causedbylocaldifferencesinradiationalheatingorcoolingmostnoticeablewhenlarge-scalewindsystemsareweakorabsentExternallydrivenlocalwinds–producedwhenstrongwindsinteractwiththelocalterrainmostnoticeablewhenstronglargescalewindsystemsarepresentCh10–LocalWindsSectionA:ThermallyDrivenLocalWindsSeabreeze–pressuredifferencesosmallthatyoucan'tobserveitintheisobarpatternsonasurfaceanalysischartitislargeenoughtocausecoolairtobeginmovingacrossthecoastlinetowardlandinlatemorning;thisistheseabreezeSeabreezecirculation–thecombinedseabreezeandreturnflowarecalledtheseabreezecirculationSeabreezefront–theboundarybetweenthecoolinflowingmarineairandthewarmerairoverlandisnarrowandwelldefinedthisfeatureisknownastheseabreezefrontCh10–LocalWindsLandBreeze–afewhoursaftersunset,thelandsurfacenearacoastlinehascooledmuchmorerapidlythanthenearbywatersurfacewhenthelandbecomescolderthantheocean,thepressuregradientacrossthecoastreversessothatthelowerpressureisoffshorethelowlevelflowwhichbeginstomovefromlandtoseaundertheinfluenceofthispressuredifferenceiscalledthelandbreezeLandbreezecirculation–thelandbreezecirculationisalsomadeupofagroundlevelbreezeandanoppositereturnflowaloft,thereverseoftheseabreezecirculationCh10–LocalWindsUpslopewind–thehillsidedeflectstheairproducingananabaticorupslopewindareturnflowisfoundabovethemountainValleyBreeze–ifthemountainsideispartofavalley,theupslopeflowmaybepartofalargerscalevalleybreezewhichisalsodirectedtowardhigherterrainthedaytimevalleybreezeflowsupthecenterlineofthevalleyandtowardthewarmslopesanopposingreturnflowisfoundaloftCh10–LocalWindsValleybreezecirculation-abovethemountaintopsaweakreturnflowknownasananti-valleywindisfoundthevalleybreezeincombinationwiththereturnflowiscalledthevalleybreezecirculationDownslopewinds–thepressuregradientreversesandkatabaticordownslopewindsdevelopalongthehillsidesMountainBreeze–onthelargerscaleofthevalleyamountainbreezeblowsdownthevalleywithareturnfloworanti-mountainwindabovethemountaintopsMountainbreezecirculation–onthelargerscaleofthevalleyamountainbreezeblowsdownthevalleywithareturnfloworanti-mountainwindabovethemountaintopsthisconfigurationisknownasthemountainbreezecirculationCh10–LocalWindsDrainagewinds–colddenseairsinkingdowntheslopesstrengthensthedownslopeandmountainbreezes,justasupslopeandvalleybreezesareintensifiedbywarmairrisinginconvectivecurrents.
GravityiseffectiveincausingtheairtomovedownwardaslongastheairneartheslopesremainscoolerthantheairawayfromthehillsatthesamelevelSmallscaleflowsofthistypearecalleddrainagewindsColdDownslopeWinds–colddenseairsinkingdowntheslopesstrengthensthedownslopeandmountainbreezesjustasupslopeandvalleybreezesareintensifiedbywarmairrisinginconvectivecurrentsCh10–LocalWindsGlacierwind–Ashallowlayerofcold,denseairflowsrapidlydowntheslopingsurfaceoftheglacier.
Gravityacceleratesthisglacierwindasitmovesdownslopesothestrongestwindsoccuratthelowerendortoeofaglacier.
Themaximumspeedsdependonthelengthandsteepnessoftheslopeoftheglacierandthefree-airtemperature.
ExtremeexamplesofsuchwindsarefoundalongthecoastofAntarctica.
Bora–AnexampleofanextremecolddownslopewindistheBora.
ItdevelopsalongthecoastoftheformerYugoslaviainthewinter.
TheterrainslopessteeplyfromtheAdriaticSeatoabout2,000feetAGL.
Gravityacceleratesshallow,coldairmassesmovingfromtheeast,downthesteepmountainslopestothesea.
Inextremecasesthecoldairreachesthecoastwithspeedsinexcessof85knots.
Ch10–LocalWindsSectionB:ExternallyDrivenLocalWindsMountainLeeWaves–whenastableairstreamflowsoveraridgeline,itisdisplacedvertically.
Downwindoftheridge,thedisplacedairparcelsacceleratebacktotheiroriginal(equilibrium)levelbecausetheairisstable.
Theyarriveattheequilibriumlevelwithsomeverticalmotionandovershootit.
Theyagainacceleratebacktotheequilibriumlevelandovershootonlytorepeatthewave-likeoscillationastheyaresweptdownstreamwiththehorizontalwinds.
Themesoscalewavepatternthattheyfollowisknownasamountainwaveormountainleewave.
Itisaparticularformofanatmosphericgravitywave.
Ch10–LocalWindsAtmosphericgravitywave–inastableatmospheregravitythroughstabilityplaysamajorroleinforcingtheparcelstoreturntoandoscillateabouttheirequilibriumlevelLeewavesystem–allleewavesregardlessoftheirgeographiclocationproducecertaincommonflowfeaturesandclouds.
Thesecharacteristicsarecapturedintheidealizedmodeloftheleewavesystem;figure10-12.
Intheleewavesystem,airflowthroughtheleewavesisindicatedbythinsolidlineswitharrows.
Themountain(green)islocatedontheleftsideofthediagram.
Thelowerturbulentzoneisshadedandcharacteristicleewavecloudsareshowninwhite.
Ch10–LocalWindsLeewaveregion–theleewavesystemisdividedintotwolayers,anupperleewaveregionwheresmoothwaveflowdominatesandmicroscaleturbulenceoccasionallyoccursandalowerturbulentzoneLowerturbulentzone–thisisfromthegroundtojustabovemountaintoplevelwhereturbulenceiscommonPrimarycycle–intheleewaveportionoffigure10-12themostintenseleewaveisthefirstorprimarycycleimmediatelydownwindofthemountain.
Successivecyclestendtohavereducedamplitudes.
Leewaveshavetheirgreatestamplitudeswithinafewthousandfeetabovethemountains,decreasingaboveandbelow.
Ch10–LocalWinds****THECONDITIONSMOSTFAVORABLETOWAVEFORMATIONOVERMOUNTAINOUSAREASAREALAYEROFSTABLEAIRATMOUNTAIN-TOPALTITUDEANDAWINDOFATLEAST20KNOTSBLOWINGACROSSTHERIDGE********CRESTSOFSTANDINGMOUNTAINWAVESMAYBEMARKEDBYSTATIONARY,LENS-SHAPEDCLOUDSKNOWNASSTANDINGLENTICULARCLOUDS****Ch10–LocalWindsCapcloud–cloudsimmediatelyoverthemountaintopsRollcloud–thecumuliformrotororrollcloudassociatedwiththerotorcumuliformandthesmoothlensshapedaltocumulusstandinglenticular(ACSL)orlenticularcloudsinthecrestsoftheleewaves.
HigherlenticularcloudsaresometimesreportedasCCSLinaviationweatherreports.
Altocumulusstandinglenticular(ACSL)/lenticularclouds-thecrestsoftheleewaveshigherlenticularcloudsaresometimesreportedasCCSLinaviationweatherreports.
Ch10–LocalWindsChinook–aChinookorfoehnisdefinedasawarmdrygustywindthatblowsfromthemountainsWarmdownslopewinds–identifiedbymanydifferentlocalnames.
AlthoughthetermsChinookandfoehnareusedwidelynowtodescribedownslopewindsinmanygeographicalareas,theyalsocomefromspecificregions.
SummaryChapter10hasshownhowthesimpleconceptofthermalcirculationisusedtoexplainthedevelopmentandgeneralfeaturesofseaandlandbreezes,mountainandvalleybreezes,anddrainagewinds.
Suchsmall-scalecirculationscancertainlyaffectflightconditions,buttheirpresenceisnotimmediatelyobviousonsurfaceanalysischarts.
Theinformationyouhavelearnedinthischapterwillhelpyouanticipatewindsproducedbylocalterrainandland-waterdifferences(Lester,2006).
SummaryAdditionally,whenlarge-scalecirculationsystemssuchasextratropicalcyclonesmaketheirwayacrossruggedterrain,interactionsoftheirwindswithmountainsandhillsproduceotheruniquemesoscalecirculationsincludingmountainleewavesandwarmdownslopewinds.
Thesephenomenaoffermanymoreseriousproblemstopilotsthandomostthermallydrivencirculations(Lester,2006).
SummaryAnaddeddifficultyarisesbecausetheconventionalnetworkofsurfaceweatherobservingstationsdoesnotobservethesemesoscalecirculationsverywell.
Therefore,thereisnotmuchdetailedinformationavailabletothepilottodetermine,forexample,thelocationandstrengthofleewavesforflightplanningandavoidancepurposes(Lester,2006).
SummaryYournewknowledgeofthemodeloftheleewavesystemandoflarge-scalepatternsfavorableforleewavedevelopmentwillproveexceptionallyvaluableinyouranalysisofthepresenceandintensityofleewaves(Lester,2006).