S-band dual-polarization radar observations of winter storms

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 KDP 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 KDP 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 KDP (and differential reflectivity ZDR) values that are consistent with the radar observations. The persistent correlation between the enhanced KDP level and the -15°C temperature regime suggests that rapidly growing dendrites likely played a significant role in the production of the observed KDP patterns. The detection of organized regions of S-band KDP 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. © 2011 American Meteorological Society.