Kusuma G Rao * and Kenji Nakamura
An attempt is made here to examine the Indian monsoon rainfall variability on seasonal, inter annual, active-break and rain-event time scales in TRMM 3B42 V7 and IMD gridded data. Inter-comparisons in rainfall composites for the TRMM period, 1998-2015, based on one-to-one data sets prepared on the common grid structure, reveal that all India seasonal mean monsoon rainfall compare well between TRMM and IMD data, however, TRMM is underestimated along the west coast, the extreme north and north-east of India. For the first time, it is shown here that the rainfall contributions of active monsoon spells to all India seasonal monsoon rainfall are at 20.76% and 21.50% in IMD and TRMM data; with the Root Mean Square Error (RMSE) at 19.2 mm day-1. Comparisons in inter annual variability of all India seasonal rainfall between the TRMM and IMD data sets are consistent with the anomalies captured with marginal differences in magnitudes. Inter-comparisons in daily rainfall between IMD and TRMM associated with Medium Rain (MR, 7.5 ≤ rain ≤ 35.4mm day-1), Heavy Rain (HR, 35.5 ≤ rain ≤ 124.4 mm day-1), Very Heavy Rain (VHR, rain ≥ 124.5 mm day-1) categories reveal that the respective RMSEs are at 10.12 mm day-1, 27.47 mm day-1 and 61.89 mm day-1 for Central India. This analysis is based on 37.4% of good data representing rain-rain data points in both IMD and TRMM data. The RMSE (Root Mean Square Error) between TRMM and IMD data for overlapping VHR category is higher by 12.6% than the average standard deviation over both the data.