Assessment of DSDs of GPM‐DPR with ground‐based disdrometer at seasonal scale over Gadanki, India

Characteristics of raindrop size distribution (DSD) obtained by Global Precipitation Measurement (GPM) mission dual‐frequency precipitation radar (DPR) are assessed over Gadanki region during southwest (SW) and northeast (NE) monsoon seasons utilizing 2 years (2014–2015) of DSD measurements by an impact‐type disdrometer. The mass weighted mean diameter (Dm in mm) and normalized DSD scaling parameter for concentration (Nw in mm−1 m−3) show pronounced seasonal differences at low to medium rain rates in the disdrometer data, in accordance with the previous studies, but not in the GPM‐DPR data. Similar features are observed every year in disdrometer measurements and over different spatial domains in GPM‐DPR measurements, indicating that sampling mismatch errors are insignificant. The reasons for the absence of seasonal differences in DSDs derived from GPM‐DPR are examined by simulating the reflectivities at Ku‐ and Ka‐bands, utilizing the disdrometer measurements and T‐matrix scattering indices. Results suggest that the Dm and Nw retrieved from single‐frequency and dual‐frequency algorithms utilizing the disdrometer data also show seasonal differences in accordance with the observations with under and overestimation of Dm and Nw, respectively. When compared with the disdrometer, the Dm values retrieved from the GPM‐DPR (official products) are severely underestimated at high rain rates (R > 8 mm h−1) during the SW monsoon season. On the other hand, during low rain rates (R < 8 mm h−1), a slight underestimation (overestimation) of Dm is seen during the SW (NE) monsoon. The mean Nw values retrieved from GPM‐DPR agree poorly with disdrometer data during both the monsoon seasons.