A New Algorithm of Rain Type Classification for GPM Dual-Frequency Precipitation Radar in Summer Tibetan Plateau

Abstract

In this study, a new rain type classification algorithm for the Dual-Frequency Precipitation Radar (DPR) suitable over the Tibetan Plateau (TP) was proposed by analyzing Global Precipitation Measurement (GPM) DPR Level-2 data in summer from 2014 to 2020. It was found that the DPR rain type classification algorithm (simply called DPR algorithm) has mis-identification problems in two aspects in summer TP. In the new algorithm of rain type classification in summer TP, four rain types are classified by using new thresholds, such as the maximum reflectivity factor, the difference between the maximum reflectivity factor and the background maximum reflectivity factor, and the echo top height. In the threshold of the maximum reflectivity factors, 30 dBZ and 18 dBZ are both thresholds to separate strong convective precipitation, weak convective precipitation and weak precipitation. The results illustrate obvious differences of radar reflectivity factor and vertical velocity among the three rain types in summer TP, such as the reflectivity factor of most strong convective precipitation distributes from 15 dBZ to near 35 dBZ from 4 km to 13 km, and increases almost linearly with the decrease in height. For most weak convective precipitation, the reflectivity factor distributes from 15dBZ to 28 dBZ with the height from 4 km to 9 km. For weak precipitation, the reflectivity factor mainly distributes in range of 15–25 dBZ with height within 4–10 km. It is also shows that weak precipitation is the dominant rain type in summer TP, accounting for 40%–80%, followed by weak convective precipitation (25%–40%), and strong convective precipitation has the least proportion (less than 30%).