Tropical Cyclone - Ocean Interaction in Typhoon Fanapi (2010) - A Synergy Study Based on ITOP Observations, EnKF Data Assimilation, and Coupled Atmosphere-Ocean Models

Even though the impacts of SST cooling, warm/cold ocean eddies, storm-induced cold wakes, and other upper-ocean thermal structure (UOTS) features on TC intensity have been qualitatively demonstrated in extant studies, quantitative evaluation remains to be carried out. The lack of in-situ measurement over the ocean, especially the western North Pacific, has always been a major roadblock in limiting the progress in fully understanding the interaction between TC and ocean. It is encouraging that unprecedented in-situ atmospheric and oceanic data were obtained from dropwindsondes, floats, and drifters deployed by aircrafts, and moorings, gliders, and drifters deployed by research vessels for the case of Typhoon Fanapi (2010) in the western North Pacific during ITOP (Impact of Typhoons on the Ocean in the Pacific). In this study, a comprehensive full-physics coupled atmosphere-ocean model based on WRF model and 3D-PWP ocean model is used to simulate Typhoon Fanapi with the initial atmospheric and oceanic field based on the observations during ITOP. In order to construct a reasonable initial storm structure, the 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 profiles obtained during ITOP, are performed to quantify the impact of ocean on the storm-induced cold wake and storm intensity. The results of simulation are also compared with the observation from satellites and the in-situ measurement during ITOP.