S-Band Dual-Polarization Radar Observations of Winter Storms

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 similar to 0.15 degrees-0.4 degrees km(-1) in an elevated layer near the -15 degrees 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 similar to 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 degrees 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 similar to 0.1 degrees-0.2 degrees km(-1) in winter storms may therefore be useful in identifying regions of active dendritic particle growth, as a precursor to aggregate snowfall.