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

Journal Article · 09 February 2018 · Journal of Applied Meteorology and Climatology

DOI: https://doi.org/10.1175/jamc-d-17-0114.1 · OSTI ID:1420031

Schrom, Robert S. ^[1]; Kumjian, Matthew R. ^[1]

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1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Meteorology and Atmospheric Science

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 (K_DP), and differential reflectivity (Z_DR), with the largest Z_DR 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 Z_DR 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.

• Research Organization: Pennsylvania State Univ., University Park, PA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER)
• Grant/Contract Number: SC0013953
• OSTI ID: 1420031
• Alternate ID(s): OSTI ID: 1541812
• Journal Information: Journal of Applied Meteorology and Climatology, Vol. 57, Issue 2; ISSN 1558-8424
• Publisher: American Meteorological SocietyCopyright Statement
• Country of Publication: United States
• Language: English