Tropical Cyclone – Ocean Interaction in Typhoon Fanapi (2010) during ITOP

Even though the roles of ocean eddies, cold wakes, and upper-ocean thermal structure (UOTS) on tropical cyclones have been qualitatively demonstrated in extant studies, impact of UOTS on TC intensity remains to be quantified. The lack of in situ measurement over the ocean has always been a major roadblock in limiting our progress in understanding the interaction between TC and ocean more thoroughly and quantitatively. It is encouraging that unprecedented in situ atmospheric and oceanic data were obtained for the case of Typhoon Fanapi (2010) in the western North Pacific from dropwindsondes, floats, and drifters deployed by airplanes, and moorings, gliders, and drifters deployed by research vessels during ITOP (Impact of Typhoons on the Ocean in the Pacific). In this study, we use a comprehensive full-physics coupled atmosphere-ocean model based on WRF model and PWP ocean model to simulate Typhoon Fanapi with the atmospheric and oceanic data obtained during ITOP. In order to have a reasonable initial typhoon structure, a new TC initialization method based on Ensemble Kalman Filter (EnKF) is applied before conducting the high-resolution coupled model simulation. Numerical experiments with different initial temperature profiles of the upper ocean, including the climatology and the data obtained during ITOP, are performed to quantify the impact of ocean on the storm-induced cold wake and intensity of Fanapi. The simulation is also compared with the observation from satellites and the in situ measurement during ITOP.

Several high-resolution sensitivity experiments are conducted in this study to quantify the impact of ocean eddies on the storm-induced cold wakes, as well as the storm intensity. The sensitivity experiments with different sizes of warm/cold eddy and its locations related to the storm, including different directions and distances, are also studied.