P-33

Development of a Two-way Nested LETKF System for Cloud-resolving Model

H. Seko (MRI, AICS, JST, JAMSTEC), T. Tsuyuki (MRI), K. Saito (MRI, JAMSTEC), T. Miyoshi (RIKEN)

A two-way nested Local Ensemble Transform Kalman Filter (LETKF) system has been developed to improve the accuracy of numerical forecasts on local heavy rainfalls. In this system, mesoscale convergence which drives local heavy rainfalls, is first reproduced by the LETKF with a grid interval of 15 km (Outer LETKF) which assimilates conventional data. The convection cells associated with the local heavy rainfall are then reproduced by the higher resolution LETKF with a grid interval of 1.875 km (Inner LETKF) which assimilates local data. The boundary conditions of the Inner LETKF are given by the forecast of the Outer LETKF, and the forecast results of the Inner LETKF are reflected into the Outer LETKF. This system was applied to a local heavy rainfall event on the Osaka Plain. The rainfall distributions similar to the observed ones were reproduced in a few ensemble members of the Inner LETKF, although the observed scattered convection cells were expressed as weak rainfall regions in the Outer LETKF. When the precipitable water vapor obtained by GPS and radial wind data observed by Doppler radars were assimilated in the Inner LETKF, the number of ensemble forecasts, which reproduced the local heavy rainfall, increased.