On the role of mesoscale ocean features on tropical cyclone-induced response.

摘要

Upper ocean response during the passage of hurricane Gilbert in the Gulf of Mexico is investigated based on high resolution observations and a three-dimensional numerical model. Oceanic observations indicated the presence of a Loop Current Warm Core Eddy (LCWCE) in the Gulf prior to the passage of the storm. Based upon conservation of heat and mass, the three-dimensional mixed layer processes are quantified from the data. Horizontal advection due to geostrophic velocities is significant in the eddy regime, suggesting that pre-storm, oceanic variability is important when background flows have the same magnitude as the mixed layer current response. Entrainment mixing is the dominant mechanism in the mixed layer and near-inertial shears at the mixed layer base indicate continued entrainment events up to the third day after storm passage.; The Miami Isopycnic Coordinate Ocean Model (MICOM) is initialized with realistic, climatological and quiescent conditions. Ocean response simulations indicate a clear modulation of the mixed layer temperatures (MLTs) and mixed layer depths (MLDs) by the LCWCE because of horizontal advection. Surface fluxes contributed up to 35% to the mixed layer cooling, and thus are important in the MLT evolution, and to the intensity of the storm. Comparison of simulated temperatures show improved agreement with the data for the realistic initial conditions.; Spatial and temporal evolution of mixed layer temperature and depth in the model are examined for four mixing parameterizations. Based on linear regression analysis, MLTs simulated using a closure scheme that depends only on near-inertial shears at the layer base fit the data better than the other three schemes. While the rates of simulated cooling and deepening differ for the four schemes, the pattern remains qualitatively similar. These numerical experiments demonstrate the need to evaluate the use of entrainment mixing schemes in the dynamics of a strongly forced oceanic mixed layer. Accordingly, high resolution measurement of background ocean conditions and currents in the upper ocean are essential for predictions of ocean heat potential and hurricane intensity change.