Air-Sea Coupling-Induced Asymmetry in Hurricane Boundary Layer and Surface Fluxes

Forecasting hurricane structure and intensity change remians to be a challenging task, especially when storm moving over the complex ocean features, such as the Gulf Stream and warm eddies, which can result in a rapid intensification in some hurricanes under a favorable atmospheric environment. However, storm-to-storm variability is large. The lack of understanding of the full coupling process at the air-sea interface and its effects on storm structure has contributed to the relatively low skills in forecasting hurricane intensity change. This study focus on the air-sea coupling induced asymmetry in the atmospheric boundary layer, the ocean mixed layer, and the air-sea fluxes and their impact on storm structure using a fully coupled atmospheric-wave-ocean model. This model is consisted of the 5th generation Pennsylvania State University / National Center for Atmospheric Research mesoscale model (MM5), WAVEWATCH III (WW3), and the 3D Price-Weller-Pinkel (3DPWP) upper ocean model. Coupled model simulations of Hurricane Katrina are used in this study. To examine the coupling related the atmospheric and oceanic boundary layer processes, a more realistic upper-ocean initial condition based on the full physics Hybrid Coordinate Ocean Model (HYCOM) assimilation fields at 0000UTC 26 August 2005 is used. Experiments with and without WW3 are also compared to highlight the influence of the ocean surface waves. To fully understand the physical processes, a comprehensive analysis of the storm and boundary layer structure in the coupled model experiments and the efficiency of the warm ocean eddy with both varied eddy position and different initial vortex intensity are underway.