The western North Pacific has the highest concentation and most destructive tropical cyclones in the world. South China Sea (SCS), which is the largest marginal seas of western north Pacific and adajcent to the TCs main development region of the western north Pacific, suffers the most frequent tropical cyclones (TCs) in the world, potentially imposing devastating threats to nearly half-billion coastal residents of East and Southeast Asia, to the flourishing fishery, oil and natural gas industries, and to the mostly used maritime routes. However, despite of favorable atmosphere and ocean conditions, intense (catagory 3 and above) TCs in SCS are surprisingly rare with the smallest area-averaged percentage number-count in the world. Previous studies may attributed the lack of intense TCs to the limited ocean basin size for intense TCs to intensify, but we can still surveille intense TCs in similar oceans, such as the Gulf of Mexico, Bay of Bengal.
During the half-year visiting to University of Hawaii (2016.03.29-2016.09.25), Dr. Fei-Fei Jin and I evaluated the suppressive effects of internal tides on the intensification of tropical cyclones in the South China Sea, through a comprehensive comparison with respect to open oceans. We show evidences to demonstrate that intense TC intensification is largely muted when TCs encounter the world’s most powerful ocean internal tides (ITs) in SCS. SCS TCs greatly amplify the vertical mixing and entrainment because of the prsence of the strong background ITs and thus induce strong sea surface temperature (SST) cooling. As the result, SCS features largest SST cooling, smallest enthalpy flux to TCs and hence the lowest TC intensification rate, especially for intense TCs, when compared with all other TC actively regions. This uncovering of the important role of SCS ITs in suppressing TC intensity may have impications in TC intensity forecasting and TC activity prejecting in the future warming climate.
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