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    Drag-Induced Transfer of Horizontal Momentum between Air and Raindrops

    Source: Journal of the Atmospheric Sciences:;2005:;Volume( 062 ):;issue: 007::page 2205
    Author:
    Shapiro, Alan
    DOI: 10.1175/JAS3460.1
    Publisher: American Meteorological Society
    Abstract: A theoretical model for unsteady drag-induced transfer of horizontal momentum between air and raindrops in moderate to heavy rainfall is presented. The model accounts for a two-way coupling in which the relative horizontal motion between air and raindrops appears as a drag forcing in both the air and raindrop equations of motion. Analytical solutions of these coupled equations are obtained for the case of rain falling through (i) an initial step change in environmental wind, (ii) a uniform shear profile, and (iii) periodically varying vertical shears of various wavenumbers (a crude proxy for turbulent eddies). Formulas for the propagation (descent) speeds of the shear zones are obtained for (ii), (iii), and for the later stage of (i). However, these speeds are generally quite small?on the order of a few centimeters per second even for heavy rainfall. More importantly, the solutions of (i) and (iii) indicate that the drag interaction leads to a decay of the velocity gradients. A formula for the e-folding decay time of the periodically varying shear profiles indicates that at small wavelengths, the smallest decay times are found for the smaller drops, but at large wavelengths, the smallest decay times are found for the larger drops. The decay times decrease with decreasing wavelength, and approach a value equal to the reciprocal of the product of the rainwater mixing ratio and a drag parameter in the limit of vanishing wavelength. For parameters typical of moderate to heavy rainfall, the small-scale decay times are on the order of a few minutes.
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      Drag-Induced Transfer of Horizontal Momentum between Air and Raindrops

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    http://yetl.yabesh.ir/yetl1/handle/yetl/4218006
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    contributor authorShapiro, Alan
    date accessioned2017-06-09T16:52:15Z
    date available2017-06-09T16:52:15Z
    date copyright2005/07/01
    date issued2005
    identifier issn0022-4928
    identifier otherams-75647.pdf
    identifier urihttp://onlinelibrary.yabesh.ir/handle/yetl/4218006
    description abstractA theoretical model for unsteady drag-induced transfer of horizontal momentum between air and raindrops in moderate to heavy rainfall is presented. The model accounts for a two-way coupling in which the relative horizontal motion between air and raindrops appears as a drag forcing in both the air and raindrop equations of motion. Analytical solutions of these coupled equations are obtained for the case of rain falling through (i) an initial step change in environmental wind, (ii) a uniform shear profile, and (iii) periodically varying vertical shears of various wavenumbers (a crude proxy for turbulent eddies). Formulas for the propagation (descent) speeds of the shear zones are obtained for (ii), (iii), and for the later stage of (i). However, these speeds are generally quite small?on the order of a few centimeters per second even for heavy rainfall. More importantly, the solutions of (i) and (iii) indicate that the drag interaction leads to a decay of the velocity gradients. A formula for the e-folding decay time of the periodically varying shear profiles indicates that at small wavelengths, the smallest decay times are found for the smaller drops, but at large wavelengths, the smallest decay times are found for the larger drops. The decay times decrease with decreasing wavelength, and approach a value equal to the reciprocal of the product of the rainwater mixing ratio and a drag parameter in the limit of vanishing wavelength. For parameters typical of moderate to heavy rainfall, the small-scale decay times are on the order of a few minutes.
    publisherAmerican Meteorological Society
    titleDrag-Induced Transfer of Horizontal Momentum between Air and Raindrops
    typeJournal Paper
    journal volume62
    journal issue7
    journal titleJournal of the Atmospheric Sciences
    identifier doi10.1175/JAS3460.1
    journal fristpage2205
    journal lastpage2219
    treeJournal of the Atmospheric Sciences:;2005:;Volume( 062 ):;issue: 007
    contenttypeFulltext
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    DSpace software copyright © 2002-2015  DuraSpace
    نرم افزار کتابخانه دیجیتال "دی اسپیس" فارسی شده توسط یابش برای کتابخانه های ایرانی | تماس با یابش
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