Atmosphere II Current Weather Finish Idealized Global Circulation Model Zonal and Meridional Flow Blocking Patterns Extratropical Cyclones For Next Class Review for exam and bring questions ID: 1017766
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1. General Circulation of the Atmosphere IICurrent WeatherFinish Idealized Global Circulation ModelZonal and Meridional FlowBlocking Patterns Extratropical CyclonesFor Next Class: Review for exam and bring questions!Reminder: Exam I on Friday (2/7)! Review sheet is posted on AsUlearn.
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7. General Atmospheric CirculationFigure 6.12
8. Winds AloftHadley cell - a north-south vertical profile of low-latitude circulation resembling a huge convection current located on either side of the ITCZ and extending to the subtropical highsSimilar cells do not occur in middle or polar latitudes
9. Global Barometric PressureFigure 6.10
10. Global Barometric PressureFigure 6.10
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12. June–July ITCZFigure 6.11
13. Zonal and Meridional FlowThe weaving westerlies have two components of motionMeridional flow - north-south airflowZonal flow - west-to-east airflowA weak meridional component (top)Cold air masses stay to the north while warm air masses remain in the southStrong meridonal component (bottom)Contrasting air masses collide, warm air overrides cold air, and encourages development of extratropical cyclones
14. Rossby WavesFigure 6.16Giant meanders in upper-level wind patterns: can range from small to large (zonal to meridional flow)
15. Zonal and Meridional FlowA strong meridional wave pattern during the winter of 2013-14Northwesterly winds brought bitterly cold arctic air into the upper Midwest and NortheasternOne of the coldest winters in decades Southwesterly winds aloft brought unseasonably mild air to far-western North America, especially the West Coast
16. January 2014What do you remember about January 2014?
17. March 13, 1993
18. Blocking Patterns and Their EffectsBlocking pattern - a cutoff low or a cutoff high that prevents the usual west-to-east movement of weather systemsOften persisting for several weeks or longerCause drought, flooding or excessive heat or cold
19. Blocking Patterns and Their EffectsA blocking circulation pattern during the summer of 1993 Record flooding in the Midwest and drought over the SoutheastSome parts of the Midwest received more than twice the long-term average seasonal rainfallSome localities in the Southeast received less than half of their long-term average seasonal rainfall
20. Blocking Patterns and Their EffectsRelative to the period 1948-2009, drought indicators describe wet or dry conditions by the probably of occurrence. Lower values (warm colors) are for dryer than normal and high values (cool colors) mean wetter than normal
21. West coast snow depth as of 15 January 2013 compared to that on the same day in 2014, when suffering from a blocking pattern
22. Blocking Patterns and Their EffectsA changing climate may also be to blame for some of the highly amplified patterns that recently seem more frequent Arctic amplification - the Arctic warming nearly twice as rapidly as the entire Northern HemisphereEncourages more meridonal flow regimes, which increases the probability of blocking patternsImplies that anthropogenic global warming is heightening the chances that some regions in the mid-latitudes could experience both exceptionally warm and cold patterns in some seasons
23. Extratropical CyclonesCyclogenesis - the birth of a cyclone, occurs along the polar front, directly under an area of strong horizontal divergence in the upper troposphereBoth short waves and long waves in the westerlies provide upper-air “lift” for the development of cyclonesWinds speed up into a ridge and weaken before a troughResulting in horizontal divergence of mid-to-upper-tropospheric winds to the east of a trough and west of a ridge
24. Supporting ProcessesJet stream - relatively narrow corridors of very strong winds within the atmosphereStrengthens in winter when the north-south air temperature contrast is greatest Weakens in summer when temperature contrasts are lessPolar front jet stream - the most prominent jet stream, located above the polar front in the upper troposphere between the midlatitude tropopause and the polar tropopause in the middle latitudes
25. Climatic Characteristics of CyclonesIdeally, a mature wave cyclone can be divided into warm and cold sectors about a low centerLowest air temperatures occur to the northwest of the storm centerContinental polar or arctic air flow southward and eastwardSteep air pressure gradient found on the west side of the surface lowStrong windsThe cold front is south of the low centerA relatively narrow band of ascending airAccompanied by cumuliform clouds, convective showers and thunderstorms
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35. Extratropical CyclonesWhere are favored locations for extratropical cyclone formation in the contiguous U.S.?
36. Climatically Favored Regions of CyclogenesisExtratropical cyclones originate and require Weak atmospheric stability, favoring ascending motion of airA nearby source of warm, humid air, which favors condensation of water vapor at low levels that releases latent heat and increases buoyancy Strong horizontal temperature gradients in the lower troposphere that give rise to frontsThe jet stream oriented above so diverging air aloft evacuates the rising air that has converged near the central low pressure
37. Climatology of Cyclone PathsAlberta Clipper - the principal tracks of cyclones that develop to the lee of the Canadian Rockies in Alberta and travel rapidly east across southern Canada or the northern tier statesNor’easter - the principal tracks of cyclones that track toward the northeast along the East Coast
38. Big IdeasPressure gradient force, Coriolis force, friction and gravity interact in initiating and affecting atmospheric circulationHorizontal and vertical air motions in anticyclones and cyclones determine weatherThe principal features of atmospheric circulation are the ITCZ, trade winds, subtropical highs, the westerlies, polar front, subpolar lows, polar easterlies and polar highs Aloft, in the middle and upper troposphere, winds blow Counter to the surface trade winds in tropical latitudes In a west-to-east wave pattern at middle and high latitudes
39. Big IdeasThrough the course of a year, components of the planetary-scale circulation shift north and south with the Sun, influencing regional climatesSynoptic scale wind and cyclone climatology emphasizes the link between the westerly winds aloft and the weather and climate of middle latitudesWesterlies produce horizontal divergence aloft for the development of cyclones, steer storms and influence air mass trajectories
40. Key TermsForcePressurePressure gradientPressure gradient forceCoriolis EffectCoriolis forceGeostrophic windGradient windWind vaneCup anemometerScatterometerSynoptic scaleMesoscaleMicroscaleSubtropical highHorse latitudesWesterliesTrade windsIntertropical convergence zone (ITCZ)Circumpoler vortexFrontFrictionMolecular viscosityEddy viscosityEddiesBoundary layerGravityPolar frontHadley cellTrade wind inversionRossby wavesMeridional flowZonal flowBlocking patternArctic AmplificationNorwegian Cyclone ModelCyclogenesisJet streamPolar front jet streamAlberta ClipperNor’easter