Identification of stratiform and convective areas using radar data with application to the improvement of DSD analysis and Z-R relations

Abstract

Previous analyses of drop size distributions (DSDs) for autumn storms in Barcelona have shown the dependency on the type of rainfall and particularly the significant differences between convective and stratiform Z-R relations. Data from the multi-site S-band radar located in Barcelona (Spain) have been used to propose an a-priori classification of the type of rainfall phases occurring on the recorded storms. For the classification two algorithms were developed: first an algorithm for the identification of convective areas based on the identification of horizontal reflectivity gradients, and second an algorithm for the bright band identification as signature of stratiform rain. With these algorithms the radar rainfall field is partitioned into three categories: i) stratiform rain, defined by the presence of the bright band over the DSD recorder, ii) convective rain, identified by the presence of strong horizontal gradients related to active convection and iii) the absence of a marked characteristic in the rainfall field. Drop size distributions from an optical disdrometer are then analyzed, both in an event-by-event approach and taking into account the a-priori classification. Although a description of the average DSD is coherent and provides acceptable results, when the analysis is performed over the stratified data the DSDs are better defined and separated into distinct types.