Improving satellite-based sub-hourly surface rain estimates using vertical rain profile information

Quantifying sub-hourly time averaged rain rate is essential information for high quality satellite rain mapping. This study proposes a novel idea to estimate sub-hourly time averaged surface rain rate based on instantaneous vertical rain profile information observed from low Earth orbiting satellites. Instantaneous rain estimates by Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) are compared with 1-minute surface rain gauges over North America for the warm seasons (April - October) of 2005 - 2014. Time-lagged correlation analysis between PR rain rates at various height levels and surface rain gauge data shows that the peak of the correlations tends to be delayed for PR rain at higher levels up to around 6 km altitude. PR estimates for low to middle height levels have better correlations with time-delayed surface gauge data than PR's estimated surface rain rate (i.e., e_SurfRain in TRMM 2A25). It implies that rain estimates for lower to middle heights may have skill to estimate the eventual surface rain rate that occurs 1 - 30 minutes later. Therefore, in this study, the vertically distributed TRMM/PR rain estimates are averaged to represent time averaged surface rain rate. It was shown that vertically averaged PR estimate up to middle heights ( 4.5 km) exhibit better skill, compared to PR's eSurfRain, to represent sub-hourly ( 30 minutes) time averaged surface rain rate. These findings highlight the merit of additional incorporation of vertical rain profiles, not only instantaneous surface rain rate, to improve sub-hourly surface estimates of satellite-based rain mapping products.