Study of Air-Sea Interactions during Typhoon “KAEMI”

Previous studies of the impacts of air-sea interaction on TC gradually agree on the significant reduction in intensity but the magnitude of reduction is not consensus. The source region of north Pacific western boundary current system is the key region of category 5 cyclones (typhoons) occurring and developing. The details of the evolution of typhoon with the air-sea interaction in this region have hardly been focused on, which is limited by the lack of observation and the imperfect numerical model. These issues are investigated numerically with a high-resolution mesoscale coupled model in the study.

In the study of "KEAMI" typhoon, the SST as an important factor of determining the magnitude of heat flux transportation is reduced when typhoon passes by and the maximum cooling rate is more than 4°C, which is related to the typhoon motion. Contrary to previous study, there is pronounced SST cooling leftward bias of typhoon track probably due to the maximum wind acceleration which releases a plenty of momentum flux into ocean and the strengthened upward convection in this region.

In terms of air-sea interaction on typhoon intensity, the SST cooling prohibits the upwelling transport of heat flux into atmosphere and the dynamical structure is changed when the downdraft is stronger than updraft according to divergence differences, which results in a weaker typhoon. Moreover, the coupling strengthens the asymmetry and gets it expanded to the lower troposphere.