Simulations of spectral polarimetric variables measured in rain at W-band

Abstract

In this work, the T-matrix approach is exploited to produce simulations of spectral polarimetric variables (spectral differential reflectivity, sZDR, spectral differential scattering phase, sHV, and spectral correlation coefficient, sρHV) for observations of rain acquired from slant-looking W-band cloud radar. The spectral polarimetric variables are simulated with two different methodologies, taking into account instrument noise and the stochastic movement of the raindrops, introduced by raindrop oscillations and by turbulence. The simulated results are then compared with rain Doppler spectra observations from W-band radar for moderate rain rate conditions. Two cases, differing in levels of turbulence, are considered. While the comparison of the simulations with the measurements presents a reasonable agreement for equi-volume diameters less than 2.25 mm, large discrepancies are found in the amplitude (but not the position) of the maxima and minima of sZDR and, more mildly, of sIHV. This pinpoints a general weakness in approximating raindrop as spheroids to simulate radar backscattering properties at the W-band.