Empirical Relations between Size Parameters of Ice Hydrometeor Populations and Radar Reflectivity

Journal Article · Thu Aug 31 00:00:00 EDT 2017 · Journal of Applied Meteorology and Climatology

DOI:https://doi.org/10.1175/jamc-d-17-0076.1· OSTI ID:1536983

Matrosov, Sergey Y. ^[1]; Heymsfield, Andrew J. ^[2]

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1. Univ. of Colorado, Boulder, CO (United States). Cooperative Inst. for Research in Environmental Sciences; National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States). Earth System Research Lab.
2. National Center for Atmospheric Research, Boulder, CO (United States)

Empirical power-law relations between the equivalent radar reflectivity factor Z_e and the slope parameter of the gamma function Λ (i.e., Λ = cZ$$^{d}_{e}$$ used to describe ice hydrometeor size distributions) are derived. The Λ parameter can also be considered as a size parameter since it is proportional to the inverse of the hydrometeor characteristic size, which is an important geophysical parameter describing the entire distribution. Two datasets from two-dimensional microphysical probes, collected during aircraft flights in subtropical and midlatitude regions, were used to obtain Λ by fitting measured size distributions. Reflectivity for different radar frequencies was calculated from microphysical probe data by using nonspherical-particle models. The derived relations have exponent d values that are approximately from -0.35 to -0.40, and the prefactors c are approximately between 30 and 55 (Λ: cm^-1; Z_e: mm⁶ m^-3). There is a tendency for d and c to decrease when radar frequency increases from K_u band (~14 GHz) to W band (~94 GHz). Correlation coefficients between Z_e and Λ can be very high (~0.8), especially for lower frequencies. Such correlations are similar to those for empirical relations between reflectivity and ice water content (IWC), which are used in many modeling and remote sensing applications. Close correspondences of reflectivity to both Λ and IWC are due to a relatively high correlation between these two microphysical parameters. Finally, expected uncertainties in estimating Λ from reflectivity could be as high as a factor of 2, although estimates at lower radar frequencies are more robust. Stratifying retrievals by temperature could result in relatively modest improvement of Λ estimates.

• Research Organization: Univ. of Colorado, Boulder, CO (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER). Earth and Environmental Systems Science Division
• Grant/Contract Number: SC0013306
• OSTI ID: 1536983
• Alternate ID(s): OSTI ID: 1673393
• Journal Information: Journal of Applied Meteorology and Climatology, Vol. 56, Issue 9; ISSN 1558-8424
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Meteorology & atmospheric sciences
clouds
precipitation
radars/radar observation