Comparison between TRMM/PR and AMeDAS ground rain gauge network in terms of annual rainfall

We have analyzed rainfall data observed by Precipitation Radar (PR) on board Tropical Precipitation Measuring Mission (TRMM) to compare with the data from AMeDAS ground rain gauge network in Japan. PR has observed latitudes of 35°N-35°S and visited Japan a few times a day. Annual rainfall amounts of 1998-2008, excluding 2001, are calculated in boxes of area size of 0.5°×0.5°-3°×3° and more. It is found that PR rainfall amounts are smaller than the Automated Meteorological Data Acquisition System (AMeDAS) rainfall amounts over Japan (~-23% in the wide area). We also estimated sampling errors and retrieval errors respectively, and found that sampling errors are sufficiently small in large areas, and retrieval errors are large and account for most of all errors. In addition, retrieval errors are small in the Seto inland sea area with light rainfall, and large in the Pacific Ocean side with heavy rainfall and the mountain district with heavy snowfall. Retrieval errors seem to depend on the rain system and geographical features. In order to investigate factors caused large errors, PR and AMeDAS rainfalls observed in same times are compared. It shows that PR has a tendency to underestimate heavy rain over 10mm/h.