Tropical Cyclone-Ocean Interaction in Typhoon Megi (2010) - A Synergy Study based on ITOP Observations and Atmosphere-Ocean Coupled Model Simulations

Even though previous observational and numerical studies have shown that tropical cyclone (TC) intensity is restrained from the TC-induced SST cooling, some of the TCs still could achieve category 5. It is encouraging that unprecedented in situ atmospheric and oceanic data were obtained for the case of Typhoon Megi (2010) in the western North Pacific, including dropwindsondes, floats, and drifters deployed by aircrafts, and moorings, gliders, and drifters deployed by research vessels during ITOP (Impact of Typhoons on the Ocean in the Pacific). In this study, the dynamics of ocean responses to super typhoon Megi is investigated by using a comprehensive full-physics high-resolution coupled model based on the WRF model and 3D-PWP ocean model, with the atmospheric and oceanic data obtained during ITOP. In order to have a reasonable initial ocean structure, the HYCOM ocean data and satellite SST are used to construct the initial ocean condition. The coupled model simulation is compared with the observation from satellites, the in-situ measurement during ITOP (2010), and the reconstructed ocean field from the NRL Eastern Asian Seas Ocean Nowcast/Forecast System (EASNFS) with the atmospheric forcing from our analysis with ITOP data assimilated.

High-resolution sensitivity experiments with different ocean mixed layer depths are further conducted to identify the criteria of the mixed layer depth which could prevent SST from being cooled by the TC-induced wind stress, and thus can retain an oceanic environment conducive for the TC development. Sensitivity experiments to different processes of oceanic dynamics, including ocean current shear-induced entrainment, horizontal advection, vertical advection, and pressure gradient, are also performed to understand the dominant mechanisms of the TC-induced cold wake.