The authors improve the high-resolution Global Satellite Mapping of Precipitation (GSMaP) product for Typhoon Morakot (2009) over Taiwan by using an orographic/nonorographic rainfall classification scheme. For the estimation of the orographically forced upward motion used in the orographic/nonorographic rainfall classification scheme, the optimal horizontal length scale for averaging the elevation data is examined and found to be about 50 km. It is inferred that as the air ascends en masse on the horizontal scale, it becomes unstable and convection develops. The orographic/nonorographic rainfall classification scheme is extended to the GSMaP algorithm for all passive microwave radiometers in orbit, including not just microwave imagers but also microwave sounders. The retrieved rainfall rates, together with infrared images, are used for the highresolution rainfall products, which leads to much better agreement with rain gauge observations.

No abstract

Rain retrieval algorithms from satellite-borne microwave radiometers (MWR) utilize lookup tables (LUTs) related between MWR brightness temperatures (Tbs) and rain intensity and databases about precipitation characteristics. Since LUT is generated to simulate Tbs from vertical rain profiles through a radiative transfer model, the accuracy of estimation in precipitation amount depends on the input vertical rain profiles. Some previous studies reported that underestimation of precipitation occurred for generated or reinforced rain systems by orography and over high elevation area. In order to improve the underestimation, orographic precipitation identification was applied to the Global Satellite Mapping of Precipitation (GSMaP) algorithm.Upward wind by topography and moisture convergence at near the surface calculated by a re-analysis data and a digital elevation map were utilized to identify areas in orographic precipitation, and a new LUT based on a warm rain case was constructed and applied to the GSMaP algorithm. In addition to the case, we examined representative vertical profiles in precipitation for above mentioned precipitation characteristics. Compared to the standard GSMaP product, clear improvement can be found for a orographic precipitation case affected by a typhoon in Taiwan.