Comparisons of Rain Rate and Reflectivity Factor Derived from the TRMM Precipitation Radar and the WSR-88D over the Melbourne, Florida, Site

Abstract

Validating the results from the spaceborne Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) requires comparisons with well-calibrated ground-based radar measurements. At altitudes near the storm top, where effects of PR signal attenuation are small, the data are used to check the relative calibration accuracy of the radars. Near the surface, where attenuation effects at the PR frequency of 13.8 GHz can be significant, the data provide an assessment of the performance of the PR attenuation correction algorithm. The ground-based data are taken from the Doppler Weather Surveillance (WSR-88D) radar located at Melbourne, Florida. In 1998, 24 overpasses of the TRMM satellite over the Melbourne site occurred during times when significant precipitation was present in the overlap region of the PR and WSR-88D. Resampling the ground-based and spaceborne datasets to a common grid provides a means by which the radar reflectivity factors (dBZ) can be compared at different heights and for different rain types over ocean and land. The results from 1998 show that the dBZ fields derived from the PR data after attenuation correction agree to within about 1 dB of those obtained from the WSR-88D with relatively minor variations (0.3 dB) in this difference with height. Comparisons of rain rates also yield good agreement with the conditional mean rain rate from the PR and WSR-88D of 8.5 and 7.6 mm h?1, respectively. The agreement improves in the comparison of area-averaged rain rates where the PR and WSR-88D yield values of 1.25 and 1.21 mm h?1, respectively, with a correlation coefficient for the 24 overpasses of 0.95.