S-Band Dual-Polarization Radar Observations of Winter Storms

Abstract

Abstract This study is based on analyses of dual-polarization radar observations made by the 11-cm-wavelength Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) system during four significant winter storms in northeastern Colorado. It was found that values of specific differential phase K DP often reached local maxima of ∼0.15°–0.4° km −1 in an elevated layer near the −15°C environmental temperature isotherm. The passage of these elevated positive K DP areas is shown to be linked to increased surface precipitation rates. Calculations using a microwave scattering model indicate that populations of highly oblate ice particles with moderate bulk densities and diameters in the ∼0.8–1.2-mm range can generate K DP (and differential reflectivity Z DR ) values that are consistent with the radar observations. The persistent correlation between the enhanced K DP level and the −15°C temperature regime suggests that rapidly growing dendrites likely played a significant role in the production of the observed K DP patterns. The detection of organized regions of S-band K DP values greater than ∼0.1°–0.2° km −1 in winter storms may therefore be useful in identifying regions of active dendritic particle growth, as a precursor to aggregate snowfall.