Comparisons of satellite and ship-borne radar precipitation estimates over the Pacific Ocean

Abstract:

Estimates of rainfall over the ocean are notoriously difficult to validate given the dearth of ground-based observations. Recently, the CSU polarimetric C-band SEA-POL radar was deployed on research vessels sailing the Pacific ocean for several field campaigns. The polarimetric capabilities of SEA-POL allow for more accurate rainfall mapping compared to single-polarization radars previously deployed on ships. Additionally, bulk microphysical characteristics can be inferred from SEA-POL, linking surface rainfall to vertical characteristics which can be compared with satellite measurements such as the GPM dual-frequency precipitation radar (DPR). Additionally, SEA-POL is used to evaluate the IMERG rainfall product which combines information from several space-borne passive and active remote sensors on an array of satellites. This study compares the derived rainfall, echo coverage areas, and convective and stratiform designations of the SEA-POL radar, GPM DPR, and IMERG. It is found that both GPM and IMERG underestimate the frequency of high intensity rain (> 60 mm/hr). IMERG tends to have large coverage area of precipitation compared to SEA-POL, but with lower rain intensities. These factors work together to produce seemingly valid integrated rain estimates, but for different reasons. These differences are investigated in terms of the spatial variability within a satellite footprint and the type of sensor.