Impact of an Ocean Model's Horizontal Resolution on the Ocean Response to a Hurricane

Hurricanes have a large impact on cooling the sea surface temperature (SST) and changing the ocean mixed layer depth. The SST is an important parameter for determining the air-sea heat fluxes and thus the intensity of a hurricane. The mixed layer depth is an important parameter for determining the depth of hurricane-induced vertical mixing in the upper ocean and the rate of SST cooling. While the SST cold wake typically decays on a time scale of days, the subsurface anomalies persist much longer and may impact the large-scale ocean circulation.

The Princeton Ocean Model (POM) is used to calculate the temperature and current profiles under a specified wind stress. One of the important parameters in an ocean model is the horizontal resolution, as finer grid spacing should allow for better representation of the hurricane eye and eyewall structure in the wind stress field. Sensitivity experiments were run for five different horizontal grid spacings: 1/2°, 1/3°, 1/6°, 1/12°, and 1/18° in latitude and longitude. Wind stress derived from an axisymmetric Holland wind field was applied over a horizontally-uniform ocean for 72 hours, with the wind stress field moving at a constant 4.8 m s^-1 translation speed. The experiments were repeated for two different radii of maximum winds (30km and 55km) and for either one-dimensional (1D) or three-dimensional (3D) ocean dynamics.

The higher resolution experiments better represent the structure of the eye and the eyewall, although little difference was seen between the 1/12° and 1/18° experiments. The lower resolution experiments showed less SST cooling and less cross-track asymmetry in the ocean response , especially to the right of the storm track. In all cases, the 3D experiments had more SST cooling than the 1D experiments, with the maximum difference of about 1°C. The spatial pattern of the mixed layer depth after storm passage varies much more dramatically in the 3D experiments than in the 1D experiments, due to the inclusion of upwelling and downwelling dynamics in the 3D experiments. It appears that higher resolution produces more SST cooling, more SST asymmetry, and enhanced mixed layer depth change than lower resolution; these differences are more pronounced with 3D ocean dynamics than with 1D ocean dynamics.