Measurements of Differential Reflectivity in Snowstorms and Warm Season Stratiform Systems
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Williams-2015-Measurements of Diff.pdf
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Author(s)
Williams, Earle R.
Smalley, David J.
Donovan, Michael F.
Hallowell, Robert G.
Hood, Kenta T.
Bennett, Betty J.
Evaristo, Raquel
Stepanek, Adam
Bals-Elsholz, Teresa
Cobb, Jacob
Date Issued
March 2015
Journal
Journal of Applied Meteorology and Climatology
Publisher
American Meteorological Society
Citation
Williams, Earle R., David J. Smalley, Michael F. Donovan, Robert G. Hallowell, Kenta T. Hood, Betty J. Bennett, Raquel Evaristo, et al. “Measurements of Differential Reflectivity in Snowstorms and Warm Season Stratiform Systems.” Journal of Applied Meteorology and Climatology 54, no. 3 (March 2015): 573–595. © 2015 American Meteorological Society
Version
Final published version
Abstract
The organized behavior of differential radar reflectivity (ZDR) is documented in the cold regions of a wide variety of stratiform precipitation types occurring in both winter and summer. The radar targets and attendant cloud microphysical conditions are interpreted within the context of measurements of ice crystal types in laboratory diffusion chambers in which humidity and temperature are both stringently controlled. The overriding operational interest here is in the identification of regions prone to icing hazards with long horizontal paths. Two predominant regimes are identified: category A, which is typified by moderate reflectivity (from 10 to 30 dBZ) and modest +ZDR values (from 0 to +3 dB) in which both supercooled water and dendritic ice crystals (and oriented aggregates of ice crystals) are present at a mean temperature of −13°C, and category B, which is typified by small reflectivity (from −10 to +10 dBZ) and the largest +ZDR values (from +3 to +7 dB), in which supercooled water is dilute or absent and both flat-plate and dendritic crystals are likely. The predominant positive values for ZDR in many case studies suggest that the role of an electric field on ice particle orientation is small in comparison with gravity. The absence of robust +ZDR signatures in the trailing stratiform regions of vigorous summer squall lines may be due both to the infusion of noncrystalline ice particles (i.e., graupel and rimed aggregates) from the leading deep convection and to the effects of the stronger electric fields expected in these situations. These polarimetric measurements and their interpretations underscore the need for the accurate calibration of ZDR.
MIT Department
Lincoln Laboratory
Massachusetts Institute of Technology. Department of Civil and Environmental Engineering
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DOI of Published Version
https://doi.org/10.1175/jamc-d-14-0020.1
