Ocean Response to Hurricane Ophelia: Observations and Simulations

Hurricanes are amongst the most destructive natural disasters known to mankind. The primary energy source driving these storms is the latent heat release due to the condensation of water vapor, which ultimately comes from the ocean. While the Sea Surface Temperature (SST) has a direct correlation with wind speeds, the oceanic heat content is dependent on the upper ocean vertical structure. Understanding the impact of these factors in the mutual interaction of hurricane-ocean is critical to more accurately forecasting intensity change in land-falling hurricanes.

The 2005 hurricane season is one of the more active hurricane seasons in recent history. Rightfully, more intense storms of this season, (i.e) Katrina, Rita and Wilma have received considerable research focus. In this paper, we focus on one of the weaker hurricanes of the season, hurricane Ophelia. During its life cycle, Ophelia moved very slowly in the Western Atlantic causing significant cooling in the upper ocean as indicated by the sea surface temperature observations from satellites and therefore presents a very special case of hurricane-ocean interaction. Here, analysis of all the available remotely sensed and in situ data are used to quantify the magnitude of the upper ocean response. In particular, available Argo profiling float data are analyzed along with the buoy data to correlate change in observed wind speeds with the upper ocean heat content changes. Maximum cooling from the satellite SST data exceeded 4 deg celsius whereas an NDBC located away from the center of the storm showed a cooling of up to 2.5 deg C. Heat content changes estimated from the in situ Argo data indicated a reduction of up to 500 MJ/m^2 after storm passage. To further understand the ocean response mechanisms, a regional model domain was set up with the Hybrid Coordinate Ocean Model (HYCOM). A detailed comparison of the numerical results with the in situ and satellite based observations will be presented in this paper. Model sensitivity to numerical parameterizations will also be discussed.