The Impact of a New Set of IASI Channels on the Unified Model Global Precipitation Forecast

Abstract

This study attempts to assess the impact of data assimilation with newly selected Infrared Atmospheric Sounding Interferometer (IASI) channels on the global precipitation forecast, using the Korea Meteorological Administration (KMA) Unified Model (UM) system. The new IASI channels assimilated under the clear-sky condition give a positive impact on the global precipitation forecast, shown in the trial experiments. In particular, the overestimated horizontal size of forecasted precipitation in the control run with operational IASI channels significantly decreases in the experimental trial with the newly selected channels. In addition, the moist biases of moisture field in the model analysis as an initial condition are substantially reduced in the experiment run. Considering that the moisture in the troposphere is a main source of precipitation, the reduction of moist biases in the troposphere seems to contribute to the improvement of precipitation forecast in the UM system. Therefore, these results suggest that the improved moisture field even over clear areas is able to enhance the precipitation forecast accuracy. And because the difference between two trial runs is only a set of IASI channels used in the UM data assimilation system, the improved precipitation forecast is likely to due to the use of different H2O channels in the new set of IASI channel used in the experiment run, which are sensitive to the tropospheric water vapor.