Estimation of midlatitude rainfall parameters from satellite microwave radiometers using the area-time integral concept

Weather Surveillance Radar-1988 Doppler (WSR-88D) level II data and special sensor microwave imager (SSM/I) brightness temperature data were collocated to further investigate the use of the area-time integral (ATI) technique in the estimation of satellite microwave rainfall amount based on the storm area coverage information. The concept of a strong relationship between the areal extent and time duration of precipitation and the total amount of precipitation seems to have been extant in radar meteorology for some time, primarily in the tropics. This strong relationship is again demonstrated using WSR-88D data. However, it was found that this correlation strongly depends on the Z-R relationship used in computing rain rate from radar reflectivity data. This study conducted two experiments: (1) using one Z-R relationship for the whole storm rain area and (2) separating rain into two parts, convective and stratiform, and applying two Z-R relationships. The area-wide average rain rate from the storm as viewed from the satellite was calculated from the ATI formalism based on the relationships developed from the WSR-88D data, The estimates were compared with the SSM/I 85-GHz scattering algorithm estimates and verified using Next Generation Weather Radar (NEXRAD) observations and hourly rain gauge measurements. The results reveal that the ATI technique can be used as an alternative approach for determining and validating satellite precipitation parameters, The separation of convective and stratiform precipitation improved the relationship between the area-wide average rain rate and fractional rainfall area and consequently improved the accuracy of satellite rainfall estimation.