Refinements to ice particle mass dimensional and terminal velocity relationships for ice clouds: Part I: Temperature dependence

AMS Citation:
Heymsfield, A. J., A. R. Bansemer, and C. H. Twohy, 2007: Refinements to ice particle mass dimensional and terminal velocity relationships for ice clouds: Part I: Temperature dependence. Journal of the Atmospheric Sciences, 64, 1047-1067, doi:10.1175/JAS3890.1.
Date:2007-04-01
Resource Type:article
Title:Refinements to ice particle mass dimensional and terminal velocity relationships for ice clouds: Part I: Temperature dependence
Abstract: This two-part study attempts to find appropriate mass dimension and terminal velocity relationships that, when considered together with particle size distributions (PSD), agree with coincident measurements of ice water content (IWC), and with variables related to higher moments such as the mean mass-weighted fall speed. Reliable relationships are required for improving microphysical parameterizations for weather forecast models and developing methods for evaluating them, subjects addressed in detail in Part II of this study. Here, a range of values from 1.5 to 2.3 is assumed for the exponent b in the mass dimension relationship, m = aD b, where D is the maximum particle dimension, to bound its likely value for sizes above about 100 μm. Measured IWC and size spectra are used to find appropriate values for the coefficient a. It is demonstrated that all values of the exponent b, with appropriate a coefficients, can fit the IWC measurements. Coincident information on particle cross-sectional areas with the m(D) relationships is used to develop general fall velocity relationships of the form Vt = AD B. These assessments use five midlatitude, synoptically generated ice layers, and 10 low-latitude, convectively generated ice cloud layers, spanning the temperature range from -60° to 0°C. The coefficients a and A and exponent B are represented in terms of the exponent b and are shown to be temperature-dependent for the synoptic clouds and relatively independent of it in the convective clouds, a result of particle mixing through the cloud column. Consistency is found with earlier results and with analytic considerations. It is found that the fall velocity is inversely proportional to the air density to approximately the exponent 0.54, close to values assumed in earlier studies.
Subject(s):Ice particles, Cloud microphysics
Peer Review:Refereed
Copyright Information:Copyright 2007 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553) does not require the Society's permission. Republication, systematic reproduction, posting in electronic form on servers, or other uses of this material, except as exempted by the above statements, requires written permission or license from the AMS. Additional details are provided in the AMS Copyright Policies, available from the AMS at 617-227-2425 or amspubs@ametsoc.org. Permission to place a copy of this work on this server has been provided by the AMS. The AMS does not guarantee that the copy provided here is an accurate copy of the published work.
OpenSky citable URL: ark:/85065/d7bp030c
Publisher's Version: 10.1175/JAS3890.1
Author(s):
  • Andrew Heymsfield - NCAR/UCAR
  • Aaron Bansemer - NCAR/UCAR
  • Cynthia Twohy
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