Weather MapsConstant height mapsExample: Surface mapsMap has same elevation everywherePressure variesConstant pressure mapsUpper-air mapsMap has same pressure everywhereHeight variesConstant Pressure SurfaceAssume uniform surface pressure and temperature (for now)This means that constant pressure surfaces parallel to constant height surfaces (flat)Heating and coolingNow heat left side, cool right sideWarm air expands“Pushes” pressure surface upwardCold air contractsPressure surface moves downwardConstant pressure surface no longer flatHigh heights are indicative of warm air below that pressure levelWarm air is less dense than cold airAs you heat air, it expands!Low heights are indicative of cold air below that pressure levelHigh heights on a constant pressure surface are analogous to high pressures on a constant height surfaceLow heights on a constant pressure surface are analogous to low pressures on a constant height surfaceIf you only think about this in terms of “pressure always decreases with height,” you will likely get it WRONG!Trough – Valley; low heights (pressures)Ridge – High heights (pressures)In the troposphere, pressure surfaces generally slope downward from the Tropics toward the Polar Regions.Waves superposed.Summary:High heights are related to warm air below that pressure levelAnalogous to high pressures on constant height surfaceRemember: A high is a high!Low heights are related to cold air below that pressure levelAnalogous to low pressures on a constant height surfaceRemember: A low is a low!Forces in the AtmospherePressure gradient force (PGF)Coriolis forceApparent force due to rotation of earthFrictionNear-surface flow onlyGravityVertical motions onlyNewton’s Second Law says that a force is required to accelerate anythingReview of PressurePressure = Force/AreaPressure is related to the weight of the atmosphere above youGreater mass of air above a high pressure system than above a low pressure systemPressure GradientAir molecules want to flow from where there is greater pressure to where there is less pressureExtreme case: A vacuum!Increasing the pressure gradient yields greater acceleration and faster flowPressure gradient = change in pressure / distanceUnits = mb/kmTightly packed isobars – Strong pressure gradientBig change over small distanceWidely spaced isobars – Weak pressure gradientSmall change over big distancePressure gradient force directed from higher to lower pressure (or higher heights to lower heights on constant pressure surface)Acts perpendicular to isobars (or height contours)PGF causes wind to blowStronger PGF yields stronger windsRotation of Earth: Coriolis ForceViewed from North Pole, the earth rotates counter-clockwiseWind blowing on the earth is analogous to throwing the ball on a merry-go-roundMerry-go-round example:If merry-go-round is NOT moving, ball does not appear to be deflectedIf merry-go-around is moving, ball will still travel in straight path as seen from aboveBall will appear to be deflected to its right from rotating platformThrower sees ball move to his right – appears to be due to external forceCatcher actually rotates to his right (thrower’s left) out of the way of ballSame effect occurs on rotating earthViewed from over North Pole, earth rotates counter-clockwiseEarth rotates faster near equator, slower near polesAs air from equator moves northward (inward), it moves faster than the air around it and appears to be deflected eastwardYou are driving 65 mph and are passed by a car going 75 mphViewed from over North Pole, earth rotates counter-clockwiseEarth rotates faster near equator, slower near polesAs air from Pole moves southward (outward), it moves slower than the air around it and appears to be deflected westwardYou are driving 65 mph and pass a car going 55 mphIf you take a turn too fast in your car, you will be deflected outward from the axis of rotationFor eastward moving air, this corresponds to a southward deflectionThe opposite scenario occurs for a westward accelerationAir deflected inward toward axis of rotationCorresponds to a northward deflectionNorthward (south winds) moving objects – Rotate faster than ground beneath themAppear to be deflected eastwardSouthward (north winds) moving objects – Rotate slower than ground beneath themAppear to be deflected westwardEastward (west winds) moving objects – Deflected outward from axis of rotation (southward in NH)Westward (east winds) moving objects – Deflected inward toward axis of rotation (northward in NH)Coriolis Force and Latitude:Change in distance from axis of rotation with north-south greatest near Poles, zero at equatorCoriolis force maximum at Poles, minimum at equatorCoriolis Force Summary:Deflects objects to the RIGHT (not necessarily east)in NHDeflects objects to the LEFT (not necessarily west) in SHChanges the direction, not the speed of motionForce is proportional to speedMaximum at Poles, zero at EquatorDistance from axis of rotation does not change at EquatorIso means “same”Bar means “pressure”Upper-Level Maps and Forces 10/03/2012Weather MapsConstant height maps-Example: Surface maps-Map has same elevation everywhere-Pressure variesConstant pressure maps-Upper-air maps-Map has same pressure everywhere-Height variesConstant Pressure Surface-Assume uniform surface pressure and temperature (for now)-This means that constant pressure surfaces parallel to constant height surfaces (flat)-Heating and coolingoNow heat left side, cool right sideoWarm air expands“Pushes” pressure surface upwardoCold air contractsPressure surface moves downwardoConstant pressure surface no longer flat-High heights are indicative of warm air below that pressure leveloWarm air is less dense than cold airoAs you heat air, it expands!-Low heights are indicative of cold air below that pressure level-High heights on a constant pressure surface are analogous to high pressures on a constant height surface-Low heights on a constant pressure surface are analogous to low pressures on a constant height surface-If you only think about this in terms of “pressure always decreases with height,” you will likely get it WRONG!-Trough – Valley; low heights (pressures)-Ridge – High heights (pressures)-In the troposphere, pressure surfaces generally slope downward from the Tropics toward the Polar Regions.-Waves superposed.Summary: -High heights are related to warm air below that