Numerical simulations and diagnostic analysis of the interaction of three tropical cyclones in 2009

Using the U.S. National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data at 1°×1° resolution and WRF meso-scale model, the thesis carries out numerical simulations of the three tropical cyclones process, which occurred in August, 2009. The result indicates that the movement of typhoon Morakot is related with the interaction of typhoon Morakot with typhoon Goni and the typhoon Etau around the time of landfall. The result of the sensitivity experiments show that according to the principle of angular momentum conservation, when the radial of the monsoon depression changes, the typhoon´s wind speed of the part which is close to the of the monsoon low will increase, which in turn changes the typhoon track. In the presence of two typhoons, when the radial of the monsoon low decreases, the north wind becomes stronger preventing typhoon to the west of the monsoon low from moving towards north. Due to the increased south wind, the eastern part of typhoon can not move northward, and the typhoon intensity is increasing. This is verified by the results of the computation control experiment and the sensitivity experiments of the steering flow at the deep level. Therefore, when there are more than one typhoon occurred at the same time, the changes of the monsoon low should be considered.