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Title: Bulk-Density Representations of Branched Planar Ice Crystals: Errors in the Polarimetric Radar Variables

Abstract

Recent interest in interpreting polarimetric radar observations of ice and evaluating microphysical model output with these observations has highlighted the importance of accurately computing the scattering of microwave radiation by branched planar ice crystals. These particles are often represented as spheroids with uniform bulk density, reduced from that of solid ice to account for the complex, nonuniform structure of natural branched crystals. In this study, the potential errors that arise from this assumption are examined by comparing scattering calculations of branched planar crystals with those of homogeneous, reduced-density plate crystals and spheroids with the same mass, aspect ratio, and maximum dimension. The results show that this assumption leads to significant errors in backscatter cross sections at horizontal and vertical polarization, specific differential phase (KDP), and differential reflectivity (ZDR), with the largest ZDR errors for ice crystals with the most extreme aspect ratios (<0.01) and effective densities < 250 kg m-3. For example, the maximum errors in X-band ZDR are 4.5 dB for 5.6-mm branched planar crystals. However, substantial errors are present at all weather radar frequencies, with resonance scattering effects at Ka and W band amplifying the low-frequency errors. Finally, the implications of these results on the interpretation of polarimetricmore » radar observations and forward modeling of the polarimetric radar variables from microphysical model output are discussed.« less

Authors:
 [1];  [1]
  1. Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, Pennsylvania
Publication Date:
Research Org.:
Pennsylvania State Univ., University Park, PA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1420031
Alternate Identifier(s):
OSTI ID: 1541812
Grant/Contract Number:  
SC0013953
Resource Type:
Published Article
Journal Name:
Journal of Applied Meteorology and Climatology
Additional Journal Information:
Journal Name: Journal of Applied Meteorology and Climatology Journal Volume: 57 Journal Issue: 2; Journal ID: ISSN 1558-8424
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; meteorology & atmospheric sciences; cloud microphysics; ice crystals; radars/radar observations

Citation Formats

Schrom, Robert S., and Kumjian, Matthew R. Bulk-Density Representations of Branched Planar Ice Crystals: Errors in the Polarimetric Radar Variables. United States: N. p., 2018. Web. doi:10.1175/JAMC-D-17-0114.1.
Schrom, Robert S., & Kumjian, Matthew R. Bulk-Density Representations of Branched Planar Ice Crystals: Errors in the Polarimetric Radar Variables. United States. doi:10.1175/JAMC-D-17-0114.1.
Schrom, Robert S., and Kumjian, Matthew R. Fri . "Bulk-Density Representations of Branched Planar Ice Crystals: Errors in the Polarimetric Radar Variables". United States. doi:10.1175/JAMC-D-17-0114.1.
@article{osti_1420031,
title = {Bulk-Density Representations of Branched Planar Ice Crystals: Errors in the Polarimetric Radar Variables},
author = {Schrom, Robert S. and Kumjian, Matthew R.},
abstractNote = {Recent interest in interpreting polarimetric radar observations of ice and evaluating microphysical model output with these observations has highlighted the importance of accurately computing the scattering of microwave radiation by branched planar ice crystals. These particles are often represented as spheroids with uniform bulk density, reduced from that of solid ice to account for the complex, nonuniform structure of natural branched crystals. In this study, the potential errors that arise from this assumption are examined by comparing scattering calculations of branched planar crystals with those of homogeneous, reduced-density plate crystals and spheroids with the same mass, aspect ratio, and maximum dimension. The results show that this assumption leads to significant errors in backscatter cross sections at horizontal and vertical polarization, specific differential phase (KDP), and differential reflectivity (ZDR), with the largest ZDR errors for ice crystals with the most extreme aspect ratios (<0.01) and effective densities < 250 kg m-3. For example, the maximum errors in X-band ZDR are 4.5 dB for 5.6-mm branched planar crystals. However, substantial errors are present at all weather radar frequencies, with resonance scattering effects at Ka and W band amplifying the low-frequency errors. Finally, the implications of these results on the interpretation of polarimetric radar observations and forward modeling of the polarimetric radar variables from microphysical model output are discussed.},
doi = {10.1175/JAMC-D-17-0114.1},
journal = {Journal of Applied Meteorology and Climatology},
number = 2,
volume = 57,
place = {United States},
year = {2018},
month = {2}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1175/JAMC-D-17-0114.1

Citation Metrics:
Cited by: 1 work
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Figures / Tables:

FIG. 1 FIG. 1: Scatterplot of the difference in σh between the branched planar crystals and the corresponding homogeneous reduced-density plates vs the σh of the branched planar crystals; the scattering of the branched planar crystals comes from the Lu et al. (2016) database. The color of each marker indicates the ρhpmore » of the particles and the size of each marker is proportional to the inverse of aspect ratio (largermarkers indicate lower aspect ratio). Triangular markers indicate particles with a factor of 0.5 applied to the thickness–maximum dimension relationship from Auer and Veal (1970) and circular markers indicate that a factor of 1.0 is applied. The zero-error line is indicated by the dashed black contour.« less

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