Significant impacts of the TRMM satellite orbit boost on climatological records of tropical precipitation

With the unprecedented spaceborne precipitation radar (PR), the Tropical Rainfall Measuring Mission (TRMM) satellite has collected high-quality precipitation measurements for over ten years. The TRMM/PR data are nowadays extensively exploited in numerous meteorological and hydrological fields. Yet an artificial orbit boost of the TRMM satellite in August 2001 modulated the observation parameters, which inevitably affects climatological applications of the PR data and needs to be clarified. This study investigates the orbit boost effects of the TRMM satellite on the PR-derived precipitation characteristics. Both the potential impacts on precipitation frequency (PF) and precipitation intensity (PI) are carefully analyzed. The results show that the total PF decreases by 8.3% and PI increases by 4.0% over the tropics after the orbit boost. Such changes significantly exceed the natural variabilities and imply the strong effects of orbit boost on precipitation characteristics. The impacts on stratiform precipitation and convective precipitation are inconsistent, which is attributed to their distinct precipitation features. Further analysis reveal that the increased PI of stratiform precipitation is mainly due to the decreased frequencies of light precipitation, while the semi-constant PI of convective precipitation is caused by the concurrently decreased frequencies of light and heavy precipitation. A modification is applied to the post-boost PR precipitation data to retrieve the actual trends of tropical precipitation characteristics. It is found that the PI of total-precipitation approximately keeps invariable from 1998 to 2005. The total PF has no obvious trend over tropical oceans but decreases considerably over tropical lands.