YaBeSH Engineering and Technology Library

    • Journals
    • PaperQuest
    • YSE Standards
    • YaBeSH
    • Login
    View Item 
    •   YE&T Library
    • AMS
    • Journal of the Atmospheric Sciences
    • View Item
    •   YE&T Library
    • AMS
    • Journal of the Atmospheric Sciences
    • View Item
    • All Fields
    • Source Title
    • Year
    • Publisher
    • Title
    • Subject
    • Author
    • DOI
    • ISBN
    Advanced Search
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Archive

    Balanced and Unbalanced Upper-Level Frontogenesis

    Source: Journal of the Atmospheric Sciences:;1988:;Volume( 045 ):;issue: 022::page 3366
    Author:
    Reeder, Michael J.
    ,
    Keyser, Daniel
    DOI: 10.1175/1520-0469(1988)045<3366:BAUULF>2.0.CO;2
    Publisher: American Meteorological Society
    Abstract: The dynamics of frontogenesis at upper levels are investigated using a hierarchy of three numerical models. They are, in order of decreasing sophistication, the anelastic (AN), the geostrophic momentum (GM), and the quasi-geostrophic (QG) approximations to the full equations of motion. Each model is two-dimensional and assumes the same basic-state, which incorporates the frontogenetical mechanisms of confluence and horizontal shear. The dependence of the numerical solutions on the initial vertical shear of the cross-front component of the geostrophic wind, ?, and its associated along-front temperature gradient is examined in detail. For the values of ? chosen, the along-front temperature gradient is either zero (? = 0) or such that cold air is advected along the upper front (? < 0). Intercomparison of the broad-scale structure of the upper-level jet?fronts as described by the AN and GM models shows close agreement. For zero or weak shears (? = 0 s?1 or ? = ?2 ? 10?3 s?1), the solutions are essentially identical. Vertical shear in the cross-front geostrophic wind serves to increase the amplitude of the cross-front circulation and displace the subsiding branch toward the warmer air. In the cases of weak or zero shear, the dominant mechanism for generating vertical vorticity at upper levels is the stretching of preexisting vertical vorticity, whereas for stronger shear (? = ?5.741 ? 10?3 s?1) the key process becomes the tilting of horizontal vorticity into the vertical by differential vertical motion. In contrast, the QG model exhibits marked differences with its AN and GM counterparts, which become even more pronounced as |?| is increased. These differences are related largely to the neglect of vortex tilting in generating vertical vorticity in the OG model. The GM and QG models assume cross-front thermal wind balance at all time. A posteriors examination of the numerical solutions shows this to be an excellent approximation when the vertical shear in the cross-front geostrophic wind is weak. For strong vertical shear of the cross-front geostrophic wind, the unbalanced along-front ageostrophic wind is proportional to the vertical advection of the cross-front velocity. Diagnoses of these simulations reveal thermal wind balance to be less well satisfied. It is shown that in contrast to the GM and QG models, wherein the along-front ageostrophic velocity is passive and thus cannot contribute to the evolution of the jet?front system, the unbalanced along-front flow contributes significantly to the dynamics as described by the AN model.
    • Download: (1.445Mb)
    • Show Full MetaData Hide Full MetaData
    • Item Order
    • Go To Publisher
    • Price: 5000 Rial
    • Statistics

      Balanced and Unbalanced Upper-Level Frontogenesis

    URI
    http://yetl.yabesh.ir/yetl1/handle/yetl/4156104
    Collections
    • Journal of the Atmospheric Sciences

    Show full item record

    contributor authorReeder, Michael J.
    contributor authorKeyser, Daniel
    date accessioned2017-06-09T14:28:34Z
    date available2017-06-09T14:28:34Z
    date copyright1988/11/01
    date issued1988
    identifier issn0022-4928
    identifier otherams-19933.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4156104
    description abstractThe dynamics of frontogenesis at upper levels are investigated using a hierarchy of three numerical models. They are, in order of decreasing sophistication, the anelastic (AN), the geostrophic momentum (GM), and the quasi-geostrophic (QG) approximations to the full equations of motion. Each model is two-dimensional and assumes the same basic-state, which incorporates the frontogenetical mechanisms of confluence and horizontal shear. The dependence of the numerical solutions on the initial vertical shear of the cross-front component of the geostrophic wind, ?, and its associated along-front temperature gradient is examined in detail. For the values of ? chosen, the along-front temperature gradient is either zero (? = 0) or such that cold air is advected along the upper front (? < 0). Intercomparison of the broad-scale structure of the upper-level jet?fronts as described by the AN and GM models shows close agreement. For zero or weak shears (? = 0 s?1 or ? = ?2 ? 10?3 s?1), the solutions are essentially identical. Vertical shear in the cross-front geostrophic wind serves to increase the amplitude of the cross-front circulation and displace the subsiding branch toward the warmer air. In the cases of weak or zero shear, the dominant mechanism for generating vertical vorticity at upper levels is the stretching of preexisting vertical vorticity, whereas for stronger shear (? = ?5.741 ? 10?3 s?1) the key process becomes the tilting of horizontal vorticity into the vertical by differential vertical motion. In contrast, the QG model exhibits marked differences with its AN and GM counterparts, which become even more pronounced as |?| is increased. These differences are related largely to the neglect of vortex tilting in generating vertical vorticity in the OG model. The GM and QG models assume cross-front thermal wind balance at all time. A posteriors examination of the numerical solutions shows this to be an excellent approximation when the vertical shear in the cross-front geostrophic wind is weak. For strong vertical shear of the cross-front geostrophic wind, the unbalanced along-front ageostrophic wind is proportional to the vertical advection of the cross-front velocity. Diagnoses of these simulations reveal thermal wind balance to be less well satisfied. It is shown that in contrast to the GM and QG models, wherein the along-front ageostrophic velocity is passive and thus cannot contribute to the evolution of the jet?front system, the unbalanced along-front flow contributes significantly to the dynamics as described by the AN model.
    publisherAmerican Meteorological Society
    titleBalanced and Unbalanced Upper-Level Frontogenesis
    typeJournal Paper
    journal volume45
    journal issue22
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/1520-0469(1988)045<3366:BAUULF>2.0.CO;2
    journal fristpage3366
    journal lastpage3386
    treeJournal of the Atmospheric Sciences:;1988:;Volume( 045 ):;issue: 022
    contenttypeFulltext
    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
    yabeshDSpacePersian
     
    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
    yabeshDSpacePersian