Sampling of the Diurnal Cycle of Precipitation Using TRMM

The temporal sampling of tropical regions is examined using observations from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and precipitation radar (PR). It is concluded that PR estimates at any one hour, even using three years of data, are inadequate to describe the diurnal cycle of precipitation over regions smaller than 12, due to high spatial variability in sampling. It is shown that the optimum period of accumulation is 4 h. Diurnal signatures display half as much sampling error when averaged over 4 h of local time. A similar pattern of sampling variability is found in the TMI data, despite the TMI's wider swath and increased sampling. These results are verified using an orbital model. The sensitivity of the sampling to satellite altitude is presented, as well as sampling patterns at the new TRMM altitude of 402.5 km.