We examined how the topography over the Korean Peninsula influences rain retrievals from Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) measurements, in particular horizontal distribution and intensity of rain rate. It was motivated by the fact that more than 70% of Korean Peninsula is covered by complex terrains and thus microwave scattering methods are not an efficient way to detect warm rain processes because of different rain-forming mechanisms over the complex terrain area.

Simulation results using a numerical mesoscale model were used as inputs to the microwave radiative transfer model to examine the impacts of terrain, wind, and moisture on microwave scattering-based rainfall estimates. By relating numerical model outputs to radiative transfer model simulations, we derived topographical correction factors as a function of terrain slope, lower-level wind, and moisture information to modify retrieved rain rates. The developed method was then applied to TMI brightness measurements in conjunction with the Regional Data Assimilation and Prediction System (RDAPS) data produced by Korea Meteorological Administration (KMA). The corrected rain rates were compared with the rain estimates from TMI measurements alone, along with those from ground-based measurements. Results show that the method developed in this study provides an improved way to estimate rain rate over the complicate terrain areas. We were able to estimate rain rate down to the small scales and detect rainfall from TMI measurements although presence of ice phase is not distinct in the upper layer.