Comparison of vertical profile of raindrop size distribution from micro rain radar with global precipitation measurement over Western Java Island

Abstract

The NASA-JAXA Global Precipitation Measurement (GPM) mission core satellite, launched in February 2014, carries the Dual-Frequency Precipitation Radar (DPR), which retrieves the three-dimensional structure of precipitation from space, including raindrop size distribution (DSD) parameters: mass-weighted mean diameter (Dm, in mm) and normalized DSD scaling parameter for concentration (Nw, in mm−1 m−3). This study compares DSD's vertical structure from the observations of GPM and ground-based radar (24 GHz Micro Rain Radar MRR) for the first time in Indonesia, precisely in Serpong (6.359°S, 106.673°E). The vertical profile of radar reflectivity, Dm, and Nw gradient was used to express the vertical gradient of DSD in rain columns (0.75–3 km). The gradient was calculated using linear regression as a function of parameters and height. Negative values indicated a downward decrease (DD) of parameters toward the surface; while, positive rates indicated a downward increase (DI) pattern. The DI of radar reflectivity from MRR was found more dominant than that of GPM Ku-band and Ka-band, with DI/DD ratios for MRR, Ku-band, and Ka-band at 7.2, 1.1, and 2.2, respectively. The three observations showed that the DI/DD ratio for convective rain was larger than that of stratiform rain. Most of the rain profiles from GPM showed a DI gradient for Nw, with a DI/DD ratio of 1.9, different from the MRR with the ratio of 0.6 only, indicating much more dominantion of DD. Furthermore, the DI/DD ratio for Dm from GPM observation was 0.8, while for MRR it was 4.55. Thus, the vertical structure of DSD from MRR was different from the one obtained by GPM, especially in convective rain. Besides the difference in profile trends, the Nw value of MRR is much larger than GPM; on the other hand, the Dm value of MRR was found much lower. Although there were some differences in DSD's vertical structure between GPM and MRR, both instruments were able to capture seasonal and diurnal variations of the DSD parameters.