Direct validation of TRMM/PR near surface rain over the northeastern Indian subcontinent using a tipping bucket raingauge network

Abstract

The near surface rain (NSR) dataset of the Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR) 2A25 V7 was validated using 36 tipping bucket raingauges installed over the northeastern Indian subcontinent, which correspond with the rain center of the Asian summer monsoon. This raingauge network covers the Brahmaputra flood plains and mountainous areas, including the Meghalaya Plateau, which is one of the wettest places in the world. We analyzed data from 2004 to 2013, and obtained 28,207 TRMM/PR-raingauge matchups with 2,170 TRMM/PR rainy field of views. Using them, we detected a reasonable time lag of around 300 seconds between the estimates from the TRMM/PR NSR and raingauges. Significant and large underestimations of TRMM/PR NSR were detected during the monsoon season (June-September) over the large areas of Meghalaya, Sylhet, and Barak. The bias ratios were -51.3% and -35.2% for the Meghalaya and Sylhet-Barak areas, respectively. In the Meghalaya subregion, major contribution to underestimation came from moderate TRMM/PR NSR from stratiform systems, and missed detection error was secondary contributor. In Sylhet-Barak subregion, moderate TRMM/PR NSR from convective systems largely contributed. Underestimation was not detected in premonsoon season (March-May).