Comparison of TRMM TMI and PR Version 5 and 6 Precipitation Data Products Under Cyclonic Weather Conditions

In 2004, the Tropical Rainfall Measuring Mission (TRMM) Science Project released a newer version of precipitation products, i.e., version 6 (V6), from its various instruments. The V6 data products are expected to be more accurate than the previous version 5 (V5). In this letter, we have attempted to analyze V5 and V6 products from two primary sensors on the TRMM, namely, the TRMM Microwave Imager (TMI) and the Precipitation Radar (PR), to unravel the quality of the V6 products vis-a-vis that of the V5 products. It is found that there are significant changes in the TMI-derived precipitation values, but the TMI brightness temperature (Tb) has not undergone any change from V5 to V6. Thus, the retrieval algorithm must have undergone some changes from V5 to V6. While the total number of TMI raining pixels is nearly unchanged, V5 moderate rain events (1 - 5 mm ldr h^-1) are more often classified as low rain events (< 1 mm ldr h^-1) in V6. Thus, TMI-based precipitation shows larger bias, particularly at low to moderate rain rates than that in V5. This results in a depression in the average Tb at around 2 mm ldr h^-1 in the Tb-rain-rate relationship with V6 measurements, which is implausible. This dip in average Tb value further complicates the Tb-rain-rate relationship by showing a continuous rise in Tb with rain rate, which is again implausible. On the other hand, PR-based rain rates have not undergone much change from V5 to V6. The relationship between Tb from TMI and rain rate from PR also does not show any anomalous behavior.