Evaluation of Extreme Rain Estimates in the TRMM/PR Standard Product Version 7 Using High-Temporal-Resolution Rain Gauge Datasets over Japan

The Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) standard product version 7 (V7) is evaluated, particularly in terms of extreme event estimation, using rain gauge data of high-temporal-resolution over southern Japan. A 1-minute rain gauge dataset within PR's field-of-view (FOV) is desirable for the evaluation. However, such dataset included only one data match with near-surface rain rate estimates (NSR) higher than 50 mm h-1 (extreme NSR). By relaxing the spatial and temporal matchup conditions, several tens of matches with extreme NSR are obtained, and the bias ratio of extreme NSR to corresponding gauge value is calculated to range from +41% to +94%. Considering that the relaxed matchup conditions may exaggerate the positive bias, the conclusion can be made that extreme NSR has a positive bias of less than +50% in V7 and that estimates are largely reliable. A similar evaluation is performed for extreme NSR in the TRMM PR standard product version 6 (V6), which showed a bias ratio of greater than +100%. Many false extreme NSR are estimated in V6, but a large part of them are diminished in V7.