Version 7 algorithm for the TRMM Precipitation Radar

This paper presents the major changes made in the version 7 algorithm for the Precipiation Radar in the Tropical Rainfall Measuring Mission (TRMM). Changes were made in both level 1 and 2 algorithms. Among them, the major changes that affect the final rain estimates are as follows: 1) the evaluation of the error in the path-integrated attenuation (PIA), 2) the definitions of convective rain and stratiform rain, 3) the method for estimating the freezing height, 4) the estimation method, 5) the raindrop shape model, 6) the drop size distribution model for stratiform rain, 7) the ice/water mixture profile above the freezing height, and 8) the non-uniform beam filling correction.

The reason for each change is presented. The overall effect of the changes is an increase in the final estimates of annual rain by about 3.4 percent over ocean and 8.2 percent over land on average. Possible sources of error and remaining issues will also be mentioned.