Interannual Variability of Tropical Rainfall Characteristics and the Impact of the Altitude Boost from TRMM PR 3A25 Data

Global and regional interannual variations of rainfall characteristics over the tropics were examined by applying empirical orthogonal function (EOF) analysis to TRMM PR 3A25 data from December 1997 to December 2007. The TRMM PR 3A25 data and other TRMM datasets detect the interannual variation of rainfall over the tropics, in concert with the SST change, which is closely related to the El Nino/La Nina cycle, including the pseudo-El Nino periods in 2002 and 2004. In addition, we examined the impact of the altitude boost of the TRMM satellite from 350 km to 400 km in August 2001 and found that the boost affects the annual cycle in light rain rates (total, convective, and stratiform). A baseline shift occurs in the annual cycle of light convective rain rate (convRainH) with more (less) frequent occurrence before (after) the boost. In addition, amplitude changes were observed in the annual cycle of light stratiform and total rain rates with more (less) frequent occurrence before (after) the boost. However, for the interannual variation, the coherent spatio-temporal structure of the El Nino/La Nina cycle is evident, and the interannual variation does not indicate any boost impact. In contrast, for heavy convRainH, the number events decreases after the boost, especially over land; however, it is difficult to conclude that this reduction is related to the boost.