Hydrometeor classification using dual-polarized C-band Doppler weather radars: comparison to a dual-polarization Doppler profiler

The innovation of dual-polarization Doppler weather radars has improved the accuracy of precipitation estimates over the past decades. Retrieving hydrometeor types from dual-polarization weather radar data, however, remains challenging. In this study, we used a hydrometeor classification scheme from wradlib to identify hydrometeor types aloft from two C-band weather radars in the Netherlands. Four recent case studies, from 2022 and 2023, were selected. A dual-polarization Doppler profiling radar, operating at Ka-band and W-band at an elevation angle of 45 degrees, was employed as a reference. First, the output of the wradlib scheme was used to determine the hydrometeor type. Based on this classification, we selected computed scattering properties from the open access ARTS Microwave Single Scattering Properties Database. Furthermore, mixing ratios of the hydrometeors were computed by combining measured C-band reflectivities using the hydrometeor type probabilities from wradlib. The hydrometeor type determines the scattering behavior of a single precipitation particle while the mixing ratio prescribes the particle size distribution (PSD), which is determined using parametrizations as employed in the Harmonie weather model. With the PSD and the hydrometeors’ terminal fall speeds, which are also taken from Harmonie, we produced spectra of various polarimetric variables that could be compared to those derived from the profiling radar. Besides incorrect classifications resulting from the wradlib algorithm, differences between constructed and observed spectra stem from various uncertainties associated with the retrievals from the profiler. Firstly, the hydrometeor canting angle distribution affects the backscattering to the radar. Secondly, the PSD parametrizations as employed in HARMONIE have been employed, while numerous alternatives exist that could yield different results. Finally, uncertainties are associated with the conversion of 45-degree measurements from the profiling radar to vertically-pointing spectra. Nonetheless, this study offers important insights into the performance of dual-polarization C-band weather radars regarding the classification of hydrometeor types.