KINEMATICAL RELATIONS BETWEEN WIND AND PRECIPITATION DISTRIBUTIONS

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  • 1 Geophysics Research Directorate, Air Force Cambridge Research Center
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Abstract

If distributions of precipitation in the atmosphere could be understood in terms of their associated three-dimensional winds, then radar, radiosonde, and surface observations might be utilized in new ways as sources of information about the winds. In this paper, continuity equations for precipitation content of horizontally uniform updrafts, or to the cores of simple cells such as represented by showers formed in the absence of vertical wind shear. A parabolic profile of updrafts is assumed. When the precipitation profile is steady-state and the fall speed of precipitation is constant, the amount of precipitation per unit volume of air increases rapidly downward in mid-atmosphere. Near the surface, changes in the vertical are very small. Maxima of precipitation content occur aloft before steady conditions obtain throughout the updraft layer; in the steady case, maxima aloft may occur when the terminal fall speed of precipitation increases only slightly faster than the updrafts and with little increase of fall speed during their growth, as is often the case with snow. An explanation is offered for the difference between the vertical distributions of precipitation associated with widespread systems and with showers, and means for practical utilization of the results are suggested.

Abstract

If distributions of precipitation in the atmosphere could be understood in terms of their associated three-dimensional winds, then radar, radiosonde, and surface observations might be utilized in new ways as sources of information about the winds. In this paper, continuity equations for precipitation content of horizontally uniform updrafts, or to the cores of simple cells such as represented by showers formed in the absence of vertical wind shear. A parabolic profile of updrafts is assumed. When the precipitation profile is steady-state and the fall speed of precipitation is constant, the amount of precipitation per unit volume of air increases rapidly downward in mid-atmosphere. Near the surface, changes in the vertical are very small. Maxima of precipitation content occur aloft before steady conditions obtain throughout the updraft layer; in the steady case, maxima aloft may occur when the terminal fall speed of precipitation increases only slightly faster than the updrafts and with little increase of fall speed during their growth, as is often the case with snow. An explanation is offered for the difference between the vertical distributions of precipitation associated with widespread systems and with showers, and means for practical utilization of the results are suggested.

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