Upper ocean response to a hurricane.

Abstract

The upper ocean response to a moving hurricane is studied using historical air-sea data and a three-dimensional numerical ocean model. Sea surface temperature (SST) response is emphasized. The model has a surface mixed-layer (ML) that entrains according to a velocity dependent parameterization, and two lower layers that simulate the response in the thermocline. The passage of Hurricane Eloise (1975) over buoy EB-10 is simulated in detail. Model results indicate that entrainment caused 85% of the irreversible heat flux into the ML; air-sea heat exchange accounted for the remainder. The rightward bias occurs in the model solution because the hurricane wind-stress vector turns clockwise with time on the right side of the track and is roughly resonant with the ML velocity. High ML velocities cause strong entrainment and thus a strong SST response. Model comparisons with EB-10 data suggest that a wind-speed-dependent drag coefficient is appropriate for hurricane conditions. Numerical experiments show that the response has a lively dependence on a number of air-sea parameters. Nonlocal processes are important to some aspects of the upper ocean response. (from author's abstract)