Lecture 15. Upper Atmospheric Cyclone StructureET Cyclone mainly draws warm air up/poleward, cold air down/equatorward.Core of cyclone rotates counterclockwise, tilts westward with height.Long and Short WavesLong waves - 3000-5000 km ridge to trough, nearly stationary.Short waves: 1000-2000 km ridge to trough, move with 500 mb winds....not always easily distinguishable.Troughs: ‘cyclonic’ (counterclockwise - NH)spin of windsRidges: ‘anticyclonic’ (clockwise - NH) spinMovement of Short Waves Through Long WavesVorticity• Vorticity is ‘spin’ of air parcel about vertical axis.• Total or ‘absolute’ vorticity has two parts:Relative vorticity = Spin of air relative to earth+ Ambient vorticity = vertical part of earth’s spin• Ambient vorticity is large at poles, zero at equator.• Absolute vorticity only changed by stretchingLong (Rossby) waves• Are set up by the pattern of oceans, land, and mountains around the globe.• Involve little stretching or compression of air columns, so air keeps the same absolute vortici...• Named after a famous meteorologist of the 1920s and 1930s who was one of the first people to re...Storms crossing over the RockiesStorm Tracks• Surface lows disappear over the Rockies• Low formation in lee of Rockies and Gulf of Mexico• Cold highs descend from Canada behind stormsLecture 15. Upper Atmospheric Cyclone StructureET Cyclone mainly draws warm air up/poleward, cold air down/equatorward.Core of cyclone rotates counterclockwise, tilts westward with height.TWB p. 58Long and Short WavesLong waves - 3000-5000km ridge to trough,nearly stationary.Short waves: 1000-2000km ridge to trough, movewith 500 mb winds....not always easily dis-tinguishable.Troughs: ‘cyclonic’(counterclockwise - NH)spin of windsRidges: ‘anticyclonic’(clockwise - NH) spinTWB p. 55Movement of Short Waves Through Long WavesEOMVorticity• Vorticity is ‘spin’ of air parcel about vertical axis.• Total or ‘absolute’ vorticity has two parts:Relative vorticity = Spin of air relative to earth+ Ambient vorticity = vertical part of earth’s spin• Ambient vorticity is large at poles, zero at equator.• Absolute vorticity only changed by stretchingRelativeAmbientNo ambient vortPositive ambient vort.Negative ambient vort.More absolutevorticityLess absolute vorticityCompressionStretchingLong (Rossby) waves• Are set up by the pattern of oceans, land, and mountains around the globe.• Involve little stretching or compression of air columns, so air keeps the sameabsolute vorticity as it moves from W to E throughout the wave.• Named after a famous meteorologist of the 1920s and 1930s who was one ofthe first people to recognize the role of the jet stream in weather.More ambient vort in ridgeNegative rel vort in ridge, positive rel vort in trough,Same absolute vort in both.ENJet stream windsStorms crossing over the Rockies(TWB p 54)Storm Tracks• Surface lows disappear over the Rockies• Low formation in lee of Rockies and Gulfof Mexico• Cold highs descend from Canada
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