Observations and Simulations of Polarimetric, X-Band Radar Signatures in Supercells

Abstract

Polarimetric weather radars, with the additional information collected, allow one to infer scatterer and precipitation properties considerably more easily than single-polarization radars. Given the relationship between the thermodynamic, mass, and kinematic fields and the resulting structure of the microphysical quantities within convective storms, examining the polarimetric characteristics of hydrometeors and the polarimetric structure of supercells provides potentially valuable information about processes and storm-relevant variables that are currently unobservable by single-polarization radar. In this study, two previously-undocumented polarimetric signatures – the low-reflectivity ribbon and the area of anomalously low co-polar cross-correlation coefficient to the left of the bounded weak echo region – observed by two mobile, X-band, polarimetric radars are examined. Since there are appreciable differences in scattering properties of some hydrometeors at different radar frequencies and most of the past work on polarimetric signatures in supercells has used S band radar data, examples of other signatures observed by X-band radars are also presented.

Given the recent development of advanced multimoment microphysics schemes and polarimetric radar emulators, examining the polarimetric structure of simulated supercells can help elucidate the microphysical and kinematic structure of simulated polarimetric signatures. To do so, a series of idealized high-resolution simulations are performed using eight different vertical shear profiles in an attempt to investigate the relationships between observed signatures, the structure of microphysical and kinematic fields within the simulated supercells, and potential sensitivities to vertical wind shear variations. Many of the previously-observed signatures are reproduced in the simulations; results from these simulations are reported.