| dc.description.abstract | This study aims to investigate whether the salinity stratification in the East China Sea and the Yellow Sea caused the abnormal intensification of Typhoon Bavi in August 2020. The salinity stratification is caused by the freshwater input from the Changjiang River, which can form a barrier layer (BL) that reduces the sea surface cooling due to vertical mixing, favoring the development of typhoons. This study uses the COAWST coupled model, combining the atmospheric model (WRF) and the ocean model (ROMS), to simulate the three-dimensional process of Typhoon Bavi passing through the East China Sea and the Yellow Sea, and compares how the typhoon intensity changes with and without salinity stratification.
This study is divided into three parts. First, the initial fields and boundary conditions of the atmospheric model (WRF) and the ocean model (ROMS) in the coupled model are tested. The atmospheric model has good performance in simulating the typhoon track and intensity, the average track error is 39.6 km, and the average intensity error is 6 kts, indicating that the model can accurately simulate the interaction between the typhoon and the environmental wind field. In the ocean model, three global ocean models, HYCOM, GLORYS, and ORAS5, are used for initial field testing. The results show that GLORYS has a better performance in simulating the ocean characteristics in the East China Sea and Yellow Sea regions, and therefore is selected as the initial field of the ocean model for the subsequent coupled model.
The second part of the study tests the simulation effects of three vertical mixing parameterization schemes (LMD, MY2.5, GLS) on the sea surface temperature cooling (SSTC) caused by typhoons in the East China Sea and Yellow Sea regions. The experimental results show that after the typhoon passes, the sea surface temperature under and to the right of the typhoon path experiences significant cooling and intense vertical mixing. Among the three schemes, the LMD scheme presents the strongest cooling effect, while the MY2.5 scheme is the weakest. Although there are certain differences between the simulation and satellite observations, overall, the LMD scheme is closest to the observations in simulating SSTC, so the LMD scheme is chosen as the vertical mixing parameterization scheme in the coupled model.
The third part conducted two simulations, one simulating a real ocean with salinity stratification, and the other replacing the ocean salinity with the same value, an ocean environment without salinity stratification. The comparative experimental results of having and not having salinity stratification show that in the experiment without salinity stratification, the maximum SSTC caused by the typhoon is about 3°C less than the salinity stratification experiment, the ocean surface cooling is weaker, the latent heat flux obtained by the typhoon is 9.5% more, the latent heat flux is higher, making the typhoon stronger. In the case of salinity stratification, when the typhoon passes, the sea surface cools more strongly, the latent heat flux is less, thereby making the typhoon relatively weaker. | en_US |