MAIN FACTORS OF THE DIFFERENCES IN RAIN RATES ESTIMATED BY TRMM/PR STANDARD ALGORITHM VERSION7 AND VERSION8

Abstract

 Precipitation Radar (PR) onboard the TRMM satellite was operated for more than 17 years and the standard algorithm has been developed up to version 7 (V7). The standard algorithm version 06 originally developed for GPM’s Ku-band radar (KuPR) is ported to be applied to PR measurements and it is treated as PR standard algorithm version 8 (V8). In this study, rain rates R estimated by V7 and V8 are compared. (1) calculation of measured radar reflectivity factor Z_m, (2) attenuation correction and (3) conversion from attenuation-corrected radar reflectivity factor Z_e to R are considered as factors of the differences in R. (1) In V8, Z_m is higher because of the recalibration of PR, which increases R by about 17%. (2) attenuation correction does not affect the average value of R as siginificantly as (1) and (3). (3) In V8, as ε estimated by attenuation correction is generally smaller than V7, and smaller R is resulted from Z_e. On the other hand, R more than several ten mm/h is estimated more frequently in V8, because the upper limit of ε is not used.