Abstract
This study conducted data assimilation experiments using the operational mesoscale four-dimensional variational data assimilation (4D-Var DA) system for Mesoscale Model (MSM) and three-dimensional variational data assimilation (3D-Var DA) system for Non-hydrostatic Model (NHM) of the Japan Meteorological Agency (JMA). Experiments investigated the impacts of GPS-derived water vapor and Doppler radar-derived radial wind (RW) on precipitation prediction for a heavy rain event on 21 July 1999. Mesoscale model (MSM) is a hydrostatic model with the horizontal grid interval of 10 km. If the only conventional meteorological data was assimilated into MSM, precipitation regions were generated over a mountainous area far from Tokyo. If GPS-derived water vapor data, RW data, and conventional data were all simultaneously assimilated, the precipitation position was modeled correctly, and precipitation onset occurred as observed. However, the intensity of the precipitation was much weaker than observed one. The fields obtained by MSM-4DVar DA system were used as the initial condition of NHM, which was expected to improve intensity of precipitation. However, the convections over the southern Kanto were not reproduced. To strengthen updraft, RW data was further assimilated by NHM-3DVar DA system. The convective cells were also considered by saturating water vapor at intense updraft grids within the precipitation region. Evolution of the precipitation system was considered by introducing rain water, snow estimated from observed reflectivity fields, and relative humidity (RH) at the grids of downdraft within the precipitation region. From this modified condition, intense convective system was well reproduced by NHM.
Published Version
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