Code 613.1 Seminar: Dr. Shoichi Shige

Department of Aerospace Engineering, Osaka Prefecture University
The Tropical Rainfall Measuring Mission (TRMM) version-6 rainfall products show variability in the biases between Precipitation Radar (PR) and TRMM Microwave Imager (TMI) rainfall estimates across the equatorial Pacific. The PR is less than the TMI over the east Pacific, while they are in good agreement over the west Pacific, resulting in reverse west-east gradients of rainfall. We investigate consistency between TMI-observed brightness temperatures (TBs) at 19 GHz channel and those simulated from the PR and TMI rainfall estimates using a radiative transfer model. Discrepancies between observed TBs and simulated ones from PR are larger for the east Pacific than for the west Pacific, indicating that PR underestimates rainfall over the east Pacific. Larger population of warm rain and less precipitation-sized ice of stratiform rain are found in the east Pacific compared to the west Pacific. This suggests more maritimity (i.e., more small to medium size raindrops) of the drop size distribution (DSD) in the east Pacific than the initial DSD model of PR2A25, representative of "maritime". Akin to orographic lifting, the strong low-level upward motion in the east Pacific where meridional SST gradients are strong presumably have active cloud drop coalescence and produce a large number of small raindrops and, hence, the PR underestimate of rainfall.