A Two-way Coupled Modeling Study of Atmosphere-Ocean Interactions during Hurricane Frances (2004)

The prediction of hurricane intensity is a very challenging problem. The high winds associated with hurricanes increase the surface mixing and change the sea surface temperature distribution, which then modifies the surface flux distributions and this further affects the intensity and path of hurricanes. In this study, we use an air-ocean coupled model to investigate how the ocean responds to Hurricane Frances (2004).

Our simulations use the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPSŪ¹), which has a nonhydrostatic moving nested grid atmospheric model, and the NRL Coastal Ocean Model (NCOM). Three nested grids (27 km, 9 km, and 3 km) are used in the COAMPS atmospheric model to simulate Hurricane Frances. The 3 km grid moves with the hurricane center during the forecast. NCOM uses one grid with 3 km grid spacing. A coupler is used to handle the flux transfers from the atmosphere to the ocean, and vice versa between the ocean domain and three nested atmosphere domains.

Our preliminary results show that the circulation of Hurricane Frances causes a cooling in the SST on the right side of the hurricane path extending outward to about 100 km. The center of the cold SST area is about 8-10 hours behind the hurricane center and is associated with the ocean upwelling. The simulated SST cooling in the wake of Hurricane Frances is consistent with AMSR/TMI satellite SST imagery. Our simulations suggest that the SST and surface currents are very sensitive to the atmospheric forcing. The 3 km resolution forcing results in a cold pool that is larger than those found with 9 km and 27 km surfacing forcing. A stronger hurricane circulation is resolved on the 3 km grid and these stronger winds result in faster ocean responses, a larger area of cooling, and a deeper ocean mixed layer than a weaker atmospheric forcing from the coarser meshes.

¹COAMPSŪ is a registered trademark of the Naval Research Laboratory.