Over the Pacific, the Comprehensive Pacific Rainfall Database (PACRAIN) of 24h rain gauge observations is utilized as reference data. The evaluation is performed on two different terrain types: low-lying atoll sites (assumed to represent open-ocean conditions) and coastal and island sites (over land). The results show that TRMM 3B42 has good skill at detecting intense TC rainfall, with good correlation and pattern matching with PACRAIN observations. However, it tends to overestimate heavy rain frequency on atoll sites, but tends to underestimate heavy rain frequency on coastal and island sites. Overall, TRMM 3B42 is better able to estimate the intensity of TC heavy rain over ocean than over land. It is least skillful at coastal and island sites with high elevation, where it significantly underestimates TC heavy rainfall, suggesting that TRMM 3B42 is unable to capture orographic enhancement during TC landfall.
The evaluation is also performed over Australia region using a high quality gauge-based gridded rainfall product from the Australian Water Availability Project (AWAP). The results show that TC intensity, location, terrain and TC seasons all have impacts on TRMM 3B42's detection skill. For TC heavy rain, TRMM 3B42 shows better agreement with AWAP during more intense TCs (CAT3-5), in eyewall as opposed to the rain bands, in tropics as opposed to sub-tropics, and in late TC seasons as opposed to early and peak TC seasons.
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