Synoptic Meteorology ATSC 5160
Popular in Course
Popular in Atmospheric Science
This 6 page Class Notes was uploaded by Tony Bode on Tuesday October 27, 2015. The Class Notes belongs to ATSC 5160 at University of Wyoming taught by Bart Geerts in Fall. Since its upload, it has received 29 views. For similar materials see /class/230349/atsc-5160-university-of-wyoming in Atmospheric Science at University of Wyoming.
Reviews for Synoptic Meteorology
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 10/27/15
Undergraduatelevel survey of the General Circulation of the Atmosphere This is a brief summary For an easyto read text you may consult a textbook eg Ackerman and Knox 2003 Chapter 7 or Wallace and Hobbs 1977 Chapter 9 more advanced 1 De nition The hemispheric or global circulation typically averaged for a period of one month or longer 2 Surface or lower atmosphere 1 4 Pressure zones A The Equatorial Trough or ITCZ latent heat release in the ascending convection produces the low also heat lows over summer subtropical continents like the Sonora low Sahara low Pakistani low NNV Australia Paraguay B The Subtropical High the horse latitudes BermudaAzoresNorthPacific southern oceans 30 N or S mainly over the oceans in summer warm High subsidence produces the surface divergence subsidence heating is offset by radiational cooling C The Arctic Low Icelandic Aleutian 60 N mainly over the oceans in winter cold core and therefore deep vertical structure graveyard of baroclinic systems resulting in surface convergence ofthe air currents from the north Pole and from the subtropical High D The Polar High the Arctic ocean in summer Antarctica yearround boreal winter continents cold core and therefore quite shallow very stable baroclinic disturbances generally ride along the edge 2 3 Prevailing most frequent lowlevel wind zones A The tropical easterlies or trade winds the winds with an east component NE E SE winds B The temperate middle latitude westerlies C The polar easterlies 3 Scell meridional circulation A Hadley cell low latitude equator to 30 degree latitudes thermally direct driven by deep convection strongest in the summer hemisphere B Ferrel cell middle latitude 30 to 60 degree latitudes weak thermally indirect meridional eddies transport heat poleward C Polar cell high latitude 60 degree latitudes to poles expanding over the winter boreal continents thermally direct but shallow 5 Causes of surface pressure variation think of SLP as the vertical integral of air mass ie temperature per unit area A Winter The ocean surface is relatively warm com pared to the nearby land at the same latitude The warmer ocean surface supports lower SLP The shallow cold highs have a high SLP because of the low verticallyintegrated temperature But cold air is so thin that the 500 mb height is low B Summer The ocean surface is relatively cool compared to the nearby land at the same latitude especially in the lowest 13 km The result is offshore high pressure Subsidence occurs above these subtropical highs making the air above the trade wind inversion as warm as that over adjacent land Very stable conditions 6 The permanent centers of action A The subtropical Highs both Pacific High and Bermuda High eXist yearround but they intensify in summer due to the relatively cooler ocean surface air that subsides aloft sustaining the surface divergence B The highmidlatitude lows are most persistent yearround around Antarctica supporting strong circumpolar westerlies over the southern ocean 7 The semipermanent centers of action A The Arctic Lows both Aleutian and lcelandic Lows B The Arctic Lows weaken and even disappear in summer 8 The seasonal variations of the strength of the centers of action A The subtropical Highs A Summer strengthen expand and their centers move over the ocean and poleward to about 40 N or S following the poleward migration ofthe zenithal sun B winter weaken shrink and their centers displace toward land and the equator about 20 N or S following the southward migration ofthe sun B The Arctic Lows A Summer weaken or disappear relatively cool oceans favors the formation ofthermal Highs and thus weakens the Lows thermal effect B Winter intensify vorticity sustained by advection of maturedecaying baroclinic systems 3 Middle and Upper Atmospheres 700 mb and higher 1 3 pressure or elevation on an isobaric surface zones A The equatorial Low up to 700 mb B The subtropical High 700 mb esp in summer over land eg Sahara producing an easterly jet at 700 mb thermal wind warmer at 2025 than at the equator A The subtropical High slopes equatorward toward the ITCZ as the elevation increases At 300 mb the ridge is over the ITCZ a The mean location of the surface subtropical High 30 N over oceans b The mean location of the 500 mb subtropical High 25 N over land B The subtropical High becomes a continuous ridge instead of separating into the Hawaiian and the Bermuda Highs C The polar Low the circumpolar vortex center The surface polar High is replaced by a Low at the 700 mb and higher levels because the cold air is associated with an upper level low lower thickness In winter the low center moves with increasing height from the oceans eg Iceland to the eastern boreal continents E Siberia E Canada 2 2 prevailing wind zones A The tropical easterlies South ofthe subtropical High to the equatorial Low In summer easterlies are found up to 30 near the surface and up to 10 at 200 mb B The polar westerlies A The circum polar vortices B From the subtropical High to the North Pole C The 1000300 mb cold air towards the poles ampboreal continents in winter establishes an upperlevel polar Low The lowlevel warm air in the south the subtropical warm Highs establishes an upperlevel High the hydrostatic equation D Stronger UL westerlies in winter than in summer the lowlevel horizontal temperature gradient is greater in winter than in summer E The westerlies expand toward the equator in winter and shrink toward the North Pole in summer following the seasonal migration ofthe sun 3 The Arctic Low A Slopes upward toward the North Pole Cold air column is associated with an upper Low the hydrostatic equation B Mean location of the surface Arctic Low 60 N or S C Location ofthe 700 mb or higher Arctic Low in summer the Pole 4 Long waves or Planetary waves quasistationary A Wavelength gt5000 km Wavelength the distance between two subsequent ridges or troughs determined by the contours on an isobaric surface B 3 mean winter Rossbywave troughs A The eastern North American seaboard 80 W From the Hudson Bay to the east coast of N America B strongest The eastern Asiatic coast 140 E over Japan C weakest The east Mediterranean sea 50 E C Causes ofthe three troughs A Troughing in lee ofthe Tibet Plateau and the Rocky mountains PV conservation B Strong horizontal temperature gradient between ocean warm boundary current and continent 6 Long wave A Stationary slowspeed B Responsible for weekly or monthly weather variations Examples heat wave flood or drought lasts for a week or longer 7 Short waves A Wavelength 1000 km 9 most obvious in the vorticity field B propagate with the flow only slightly slower C causes departures from geostrophic balance This in turn produces ageostrophic flow including vertical motion even though the atmosphere generally is stably stratified This ageostrophic flow attempts to restore geostrophic balance Vertical motion is responsible for daily weather variations 8 Jet Stream A A fastmoving upperlevel air current strong wind con ned vertically by a rapid reversal of temperature gradient sloping tropopause and horizontally by a sharp LL temperature gradient front The wind speed generally exceeds 30 ms at the SOOmb level B The thermal wind theory A The upperlevel height gradient is determined by the lowlevel horizontal temperature gradient the hydrostatic equation B A strong lowlevel horizontal temperature gradient creates a strong upperlevel height gradient and hence strong wind ajet stream C A westerly jet separated the cold air to the pole and the warm air to the equator D An easterlyjet separates the warm air poleward from cooler air equatorvvard in the tropics E Confluence Theory for frontogenesis over the ocean proposed by Namias and Clapp For instance the north Atlantic A cold air advection from northwest around the Icelandic Low sometimes continental polar coldair outbreaks B warm air advection from southwest diverging from the Bermuda High C confluence leads to frontogenesis between the High and the Low polar front resulting a strong wind zone in the upper level Small perturbations may amplify cyclogenesis they usually mature before they reach W Europe F Types of Jet A The polar front Jet mean location 47 N 35 to 60 N jet core the elevation ofthe highest wind speed 250300 mb occurs all year round but strongest in winter and near eastern shores of2 boreal continents discontinuous unsteady variable often high vorticity in trof of on cyclonic shear side Cgtf associated with a surface polar front is distorted in association with LL cyclogenesis and coldwarm advection tropopause sloped or folded middlelatitude tropopause much higher than the polar tropopause B V The subtropical jet mean location 27 N 20 to 35 N jet core 150 mb occurs in winter only lack of strong horizontal temperature gradient in the lower atmosphere in summer north of a subtropical High near a weaker tropopause slope aloft often merged with the polar jet esp on the east side ofthe large continents 9 Palmen and Newton39s General Circulation Model A The tropopause is broken into 3 sections A Tropical tropopause 1618 km sharply defined esp above the lTCZ B Middle latitude tropopause 12 km C Polar tropopause 68 km becomes illdefined in winter polar night westerly jet near 20 km B The subtropical jet gap between the tropical and middlelatitude tropopauses C Polar frontjet A The gap between the middlelatitude and polar tropopause B The polar front extends to the ground surface from thejet core observations indicate that front is weak above 800 mb and below the tropause fold 10 Conservation of absolute vorticity wave patterns of air ows A Absolute vorticity relative vorticity Coriolis parameter constant if DV0 B Vorticity the tendency of an air parcel to rotate in the same direction as the earth positive vorticity C Relative vorticity shear vorticity curvature vorticity D Conservation of absolute vorticity can be used to explain Rossby waves restoring force 3 A northerly equatorvvard flow feels decreasing plan vort leads to increased relative vorticity B An air parcel tends to change from clockwise circulation to counterclockwise circulation The air parcel changes the direction moving backtoward north 11 Vanishing storms over the Rocky Mountains lee cyclogenesis A conservation of the potential vorticity Absolute vorticityDepth of an air column constant A A ridge tends to generate or intensify over a large mountain due to the shrinking of the air column B A trough tends to generate or intensify in the lee of a large mountain due to the stretching of the air column B The Great Plains Alberta Colorado cyclogenesis cyclone formation or intensification 4 Trade wind Inversion 1 Most intense in the east part ofa subtropical high Hawaiian High for example A San Francisco in summer or Concepcion Chile orWalvis Bay Namibia A Average inversion base height 500 m B Average inversion magnitude inversion top temperature inversion base temperature 1015 C B closer to the lTCZ eg Honolulu A Average inversion base height 2000 m B Average inversion magnitude 5 C 2 Causes A Compressional heating due to the subsidence sinking of the upper level air originating from the equator B Cool surface marine layer A Cold ocean current travels from north to south B Upwelling a Rising of ocean water from below b Ekman spiral Ocean surface water ows to the right left of alongshore equatorward winds resulting in flow away from the continent inducing the rising of ocean water from below to replace the offshore surface transport