Volume 12 (2016) Pages 75-79
The impact of additional radiosonde observations during the Vietnam-Philippines Rainfall Experiment 2010 (VPREX2010) was investigated by performing observing system experiments using the local ensemble transform Kalman filter (LETKF) and the atmospheric general circulation model for the Earth Simulator (AFES). During the experimental period from 15 September to 15 October, 2010, a westward-propagating disturbance was developed in the South China Sea and caused heavy rainfall on the east coast of Vietnam and Hainan Island. By assimilating the additional radiosondes, significant increases in wind speed, temperature and specific humidity were detected in the lower troposphere around the disturbance. In addition, the analysis ensemble spread for meridional wind decreased by 5-25% across the Indochina Peninsula, Philippines Sea and western Pacific to the south of Japan. Moreover, winds became stronger around the disturbance due to the additional observations, and the ensemble spread for wind speed became larger. The results show that the disturbance in an early stage of development was not well detected in the South China Sea without the use of additional radiosonde observations. Therefore, it is suggested that continuous and intensive radiosonde observations in Vietnam and the Philippines are essential for the improvement of the objective analysis of such disturbances.