Hydrometeor classification based on ZDP using C-band radar

Discriminating between liquid and solid precipitation is a fundamental, important task in classification of precipitation by polarimetric radar. Most research efforts have so far concentrated in detection of hail, while possibilities of discriminating between rain and snow have received less attention. In the present study we use data from the University of Helsinki C-band coherent polarimetric radar to compare simple rain/snow classification schemes based on horizontal reflectivity and either the difference reflectivity or the differential reflectivity. A well defined bright band existed in most of the cases studied. Results agreed in general with the results obtained earlier by other authors. However, the possibility of dividing the horizontal reflectivity into parts corresponding to ice and liquid water with the aid of difference reflectivity did not work properly in weak precipitation or above the melting layer. Reasons for these deficiencies may be found from following two conditions conflicting with the basic assumptions of the method, namely 1) light rain consists of small spherical water droplets, and 2) oriented ice crystals are not spherical. Small water droplets are possible both below and above the melting layer, while oriented crystals are met only above the melting layer.