Typhoon rain retrievals using TMI, AMSU-A, and island gauge data sets

In this study, TRMM Microwave Imager (TMI) level-1B01 data, AMSU-A microwave data, and island gauge measurements from seven isolated islands near Taiwan were used to retrieve Typhoon rainfalls over oceans near Taiwan. One of the main purposes of this study is to establish statistical relationships between them. Several methods of correlating satellite microwave measurements to the observed island gauge data were tried, and a method involved the use of multiple linear regression to compute determination coefficients using the island gauge data as well as passive microwave multiple-channel data from either TMI or AMSU-A was adopted in this paper. This method allowed for the inclusion of different rainfall mechanisms (scattering-based and emission-based rainfall mechanisms), which had been found to be important factors in rain retrievals using passive microwave measurements. The island gauge data were treated as ground truth. The validation results show AMSU rain retrievals overestimate TMI rain retrievals. The multi-sensor technique established in this study was suitable to study the characteristics of typhoon rainfalls, especially for the analyses of rain intensities and rain distributions under cloud tops over oceans. The study results also are helpful for understanding the physical processes within typhoon rain bands, especially for those studies about data assimilation and model simulation. Ground based radar observations are expected in further research, which contribute to establish a typhoon rainfall observation net-work monitoring typhoons continuously.