Abstract
Daily rainfall datasets of 10 years (1998–2007) of Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) version 6 and India Meteorological Department (IMD) gridded rain gauge have been compared over the Indian landmass, both in large and small spatial scales. On the larger spatial scale, the pattern correlation between the two datasets on daily scales during individual years of the study period is ranging from 0.4 to 0.7. The correlation improved significantly (~0.9) when the study was confined to specific wet and dry spells each of about 5–8 days. Wavelet analysis of intra-seasonal oscillations (ISO) of the southwest monsoon rainfall show the percentage contribution of the major two modes (30–50 days and 10–20 days), to be ranging respectively between ~30–40% and 5–10% for the various years. Analysis of inter-annual variability shows the satellite data to be underestimating seasonal rainfall by ~110 mm during southwest monsoon and overestimating by ~150 mm during northeast monsoon season. At high spatio-temporal scales, viz., 1° ×1° grid, TMPA data do not correspond to ground truth. We have proposed here a new analysis procedure to assess the minimum spatial scale at which the two datasets are compatible with each other. This has been done by studying the contribution to total seasonal rainfall from different rainfall rate windows (at 1 mm intervals) on different spatial scales (at daily time scale). The compatibility spatial scale is seen to be beyond 5°×5° average spatial scale over the Indian landmass. This will help to decide the usability of TMPA products, if averaged at appropriate spatial scales, for specific process studies, e.g., cloud scale, meso scale or synoptic scale.
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