Development of a Precipitation Climate Record from Spaceborne Precipitation Radar Data. Part I: Mitigation of the Effects of Switching to Redundancy Electronics in the TRMM Precipitation Radar

Abstract

Precipitation observation with the Tropical Rainfall Measuring Mission’s (TRMM’s) precipitation radar (PR) lasted for more than 17 years. To study the changes in the water and energy cycle related to interannual and decadal variabilities of climate, homogeneity of long-term PR data is essential. The aim of the study is to develop a precipitation climate record from the 17-yr PR observation. The focus was on mitigating the discontinuities associated with the switching to redundant electronics in the PR in June 2009. In version 7 of the level-1 PR product, a discontinuity in noise power is found at this timing, indicating a change in the signal-to-noise ratio. To mitigate the effect of this discontinuity on climate studies, the noise power of the B-side PR obtained after June 2009 is artificially increased to match that of the A-side PR. Simulation results show that the storm height and the precipitation frequency detected by the PR relatively decrease by 2.17% and 5.15% in the TRMM coverage area (35°S–35°N), respectively, and that the obvious discontinuity of the time series by the storm height and the precipitation fraction caused by the switching to the redundancy electronics is mitigated. Differences in the statistics of other precipitation parameters caused by the switching are also mitigated. The unconditional precipitation rate derived from the adjusted data obtained over the TRMM coverage area decreases by 0.90% as compared with that determined from the original data. This decrease is mainly caused by reductions in the detection of light precipitation.

Calibration of the Dual-Frequency Precipitation Radar Onboard the Global Precipitation Measurement Core Observatory

“…As a result, the correction value of the PR Rx B-side system (C rB ) was 1.9 dB, and C t of the PR was −0.92 dB. Note that the PR's Rx system was switched from A-to B-side system in June 2009 on account of A-side Rx system issue [28]. Since the A-side system was not directly calibrated with the DPR-ARC, the correction value of the PR Rx A-side system (C rA ) was determined by using results of DPR-ARC and PR-ARC by taking a difference in results between those into account; then, C rA was given to be −0.37 dB.…”

“…With the new parameters, the Z m increased by about 1.1 dB relative to the V7 values. To evaluate the Z min and R min , the same methods described in Section VI-D were used as well as the DPR and we calculated them for the satellite altitudes of 350 and 402.5 km taking into account the TRMM boost [28]. As a result, Z min was 19.34 dBZ in 350-km altitude and 20.21 dBZ in 402.5-km altitude.…”

“…Although the Z min was degraded by 1.2 dB (= 20log(402.5/305)) due to the changes in the satellite altitude from 350 to 402.5 km as reported by Takahashi and Iguchi [29], our results slightly differ from them. One reason is the difference in sensitivity between A-and B-side system [28].…”

Progress from TRMM to GPM

“…System calibration was conducted using internal house-keeping data and a ground-based external active calibrator that transmitted or received radiowaves to and from the PR (Kanemaru et al 2017;Masaki et al 2020). The accuracy of data continuity was subsequently evaluated and confirmed using the statistics of rain totals, storm top height, and long-term rain total trends.…”

Examining the Consistency of Precipitation Rate Estimates between the TRMM and GPM Ku-Band Radars

“…The Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) normally operated from December 1997 to October 2014 (Kanemaru et al 2017). As a successor, the Dual-frequency Precipitation Radar (DPR) on the Global Precipitation Measurement (GPM) mission core satellite has been operating since March 2014.…”