AirMassesFrontsampMidLatitudeCyclones气团锋amp中纬气旋.pptx

Our ApproachAir MassesFrontsMid-Latitude CyclonesWeather ForecastingAir MassesDefinitionPortion of the Atmosphere with Large Horizontal Extent(100s to 1000s miles)Horizontally Uniform TemperatureHorizontally Uniform HumidityVertical Temperature Support Stability Air Masses are Energy Storage RegionsHow Do Air Masses FormAir Remains Over Uniform Surface for Several DaysHigh Pressure Helps Subsidence Enhances Stability,Clear Skies,Calm WindsAtmosphere Takes on Characteristics of Surface BeneathFactors Affecting Air Mass CharacteristicsLand vs.WaterLand Surface TypeLatitude(temperature)Season(temperature,stability)Air Mass ClassificationTemperature Related to Latitude ZonesA ArcticP PolarT TropicalE EquatorialAA-AntArcticClassification(cont.)Moisture or Humidityc Continental drym Maritime-moistAir Mass DesignationcP -Continental Polar cold and drycT Continental Tropical warm and drymP Maritime Polar cool and moistmT Maritime Tropical warm and moistAir Mass Movement and ChangeAir Masses will Eventually Move Out of Source RegionWhy Strength of High Pressure or Prevailing CirculationMovement Out Of Source Region May Change Air Mass CharacteristicsAir Mass ModificationAir Masses that Moves to a Region With a Higher Surface Temperature are Classified as a k(cold)Type Air Masse Example:a cP that forms in Eastern Canada moves over the North Atlantic where the surface temperature is Higher the Air Mass becomes cPkAir Mass is colder(k)than surface belowAir Mass Modification(cont.)Air Masses that Move to a Region With a Lower Surface Temperature are Classified as a w(warm)Type Air Mass Example:a mT that forms in the Gulf of Alaska moves over Central Canada moves c where the surface temperature is Lower the Air Mass becomes mTwAir Mass is warmer(w)than surface belowCharacteristics of Modified Air Massesk Type Air MassesAir is colder than surface belowUnstable convective clouds,good visibilityw Type Air MassesAir is warmer than surface belowStable fog,haze,poor visibilityAir Masses in ConflictWhen Air Masses Move the Possibility Exists that Two Distinctly Different Air Masses will Move Toward Each OtherWhen/If Air Masses Push Against Each Other or“Bump”Into Each Other There is a Region of Transition from Air Mass A to Air Mass BFrontsThe Boundary Between Two Distinct Air Masses is a Front(i.e.the boundary on the surface of the earth)Frontal Surface-3 Dimensional Boundary Between Two Distinct Air Masses Characteristics of a FrontSharp Contrast in TemperatureSharp contrast in Dew PointJump in PressureShift in Wind DirectionKinks in IsobarsTypes of FrontsStationary Front no movement energy storageCold Front cold air pushing into warm airWarm Front warm air pushing into cold airOccluded Front warm front catches up to cold front energy dissipationCold FrontLarge cP type air masses move out of their source regionPush Into the region of a mT and displace the warm airLifting and Clouds(Convective)close to the front(up to 50 miles behind)Unstable Conditions behind the front(cold air over worm surface)Warm Front mT Air Mass Pushes Into a cPWarm less dense air slides up over the cold airFormation of extensive region of Stratified CloudsStable Conditions Behind the Front(warm air over a cold surface)Stationary FrontBoundary between cold and warm air massesNo Motion may be precursor to development of either cold or warm frontWeak WindsLittle or No CloudsEnergy Storage ModeOccluded FrontLate Stage of Mid-Latitude CycloneCold Front Catches up to Warm FrontWarm Air is displaced UpwardMerging of Cloud and Precipitation Systems of Cold and Warm FrontRepresents a Stage of Energy DepletionMid-Latitude CycloneTraveling Wave CycloneNorwegian Cyclone ModelMajor Type of Storm System for U.S.from October through AprilRelease of Energy Stored in Air MassesEvolution of Frontal Systems