Abstract
A polarimetric radar method to estimate mean shapes of ice hydrometeors was applied to several snowfall and ice cloud events observed by operational and research weather radars. The hydrometeor shape information is described in terms of their aspect ratios, r, which represent the ratio of particle minor and major dimensions. The method is based on the relations between depolarization ratio (DR) estimates and aspect ratios. DR values, which are a proxy for circular depolarization ratio, were reconstructed from radar variables of reflectivity factor, Ze, differential reflectivity, ZDR, and copolar correlation coefficient ρhv, which are available from radar systems operating in either simultaneous or alternate transmutation of horizontally and vertically polarized signals. DR-r relations were developed for retrieving aspect ratios and their sensitivity to different assumptions and model uncertainties were discussed. To account for changing particle bulk density, which is a major contributor to the retrieval uncertainty, an approach is suggested to tune the DR-r relations using reflectivity-based estimates of characteristic hydrometeor size. The analyzed events include moderate snowfall observed by an operational S-band weather radar and a precipitating ice cloud observed by a scanning Ka-band cloud radar at an Arctic location. Uncertainties of the retrievals are discussed.
Highlights
Scanning polarimetric weather radars operating at centimeter-wavelength frequency bands, such as S (~3 GHz), C (~5 GHz) and X (~10 GHz) bands, have been long used for hydrometeor identification (HID) retrievals [1,2,3]
Quantitative information about general shapes of atmospheric ice particles is important for many practical applications such as the development of novel polarimetric snowfall quantitative precipitation estimation (QPE) methods and advanced modeling of microphysical processes involving evolution of ice hydrometeors
Depolarization ratio (DR) estimates, which are less susceptible to particle orientations compared to other polarimetric variables such as differential reflectivity, can be readily deduced from polarimetric radar variables measured directly
Summary
Scanning polarimetric weather radars operating at centimeter-wavelength frequency bands, such as S (~3 GHz), C (~5 GHz) and X (~10 GHz) bands, have been long used for hydrometeor identification (HID) retrievals [1,2,3]. The HID algorithms usually utilize a fuzzy-logic approach and are based on variables from horizontal and vertical polarization radar measurements such as the equivalent radar reflectivity factor (hereafter just reflectivity), Ze , differential reflectivity, ZDR , specific differential phase KDP , and copolar correlation coefficient, ρhv. As an output, these algorithms prescribe different dominant hydrometeor types/species for cloud and precipitation particles filling the radar resolution volume. Quantitative information on ice particle shapes, is not typically provided by the HID algorithms.
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