| dc.description.abstract | This study investigates the impact of atmosphere-ocean interactions on a massive rainfall event of 23 and 24 August 2018 over Taiwan, which associates with the tropical depression making landfall in the western portion of Taiwan. There are two ensemble forecast experiments conducting in the present study, which uses the coupled ocean-atmosphere-wave-sediment transport modeling system (COAWST) in two modes (coupled and uncoupled) and the atmospheric initial condition provided by the WRF-Local Ensemble Transform Kalman Filter (WRF-LETKF) data assimilation system.
Comparisons between the coupled and uncoupled ensemble forecasts show that the coupled run tends to have more rain than the uncoupled one from offshore to coastal region of southwestern Taiwan, a result from modifying the characteristics of weather systems by the air-sea interaction. The discrepancy in the magnitude of SST contributes to the difference in rainfall because the coupled run can simulate the SST′s diurnal cycle while the atmosphere-only uncoupled run does not. Besides, the heat fluxes play an essential role in the characteristic of this rainfall event because they are the primary sources of energy for TD′s development. In general, the uncoupled heat fluxes are stronger than that in the coupled run, especially over the offshore southeast of Taiwan. With air-sea coupling, both humidity and temperature are modified, leading to a higher latent heat flux over the open ocean southwest of Taiwan, causing the coupled run has more rainfall there.
The ensemble members of both runs are grouped into three groups with rainfall behaviors similar to, less than, or very different from the observed rainfall. The representative ensemble member from each group is used to illustrate the distinctive features corresponding to the rainfall distribution of each group with and without air-sea coupling. Generally, the uncoupled run tends to generate another low-pressure system southeast of China, which is unrealistic and contributes to the rainfall on 24 August. The emerging of this system is discouraged after air-sea coupling. | en_US |