Numerical study of typhoon-induced ocean thermal content variations on the northern shelf of the South China Sea

摘要

This paper investigates the downwelling caused by tropical cyclones near the continental shelf. A numerical ocean model is used to simulate the ocean's response to storms moving along shelf across the northern South China Sea. Five westward-moving storms from this region were selected for the study. Data on the sea surface temperature and the height deviations showed that there was an increase in the water levels and delayed cooling on the shelf to the right of the track during these storms. Such phenomena were observed in regions south of China's coast and near Hainan Island, and the model's results also revealed that subsurface warming occurred at both locations. The site south of China's coast is associated with the strong post-storm convergent phase when warm water is brought both downward and seaward generating a temperature front on the shelf. The land barrier resulted in a cross-shelf circulation, which helped to block the movement of cold water towards the shore in the following divergent phases; therefore, the downwelling front continued for several days. The site east of Hainan resulted from an interesting combination of a westward storm path and coastal topography. The position of Hainan in relation to these storms greatly diminished the off-shelf path of storm-generated flows, so the region became a significant convergence zone. Therefore, the downwelling in this region increased with the storm's approach, and the warming continued until the storm passed. These examples indicate that the tropical cyclones' influence on the ocean's upper level heat content in the shelf region can be positive and may possibly have a significant effect on local or regional weather systems.