Response of the upper ocean to hurricane Eloise.

Abstract

Buoy data provided clear evidence of mixed layer deepening and an internal wave caused by Hurricane Eloise, September 1975. Logarithmic temperature profiles below an isothermal mixed layer were assumed and used to model thermocline oscillation and heat budget calculation as influenced by Eloise over a 21-day period. Results show that prior to the arrival of Eloise at the buoy, the average mixed layer depth was about 33m. As the winds increased due to hurricane approach, the mixed layer deepened steadily to about 42m before upwelling to approximately 22m. The thermocline then underwent three distinctly large oscillations of inertial periodicity, while the mixed layer continued to deepen. The post-storm average mixed layer depth was about 52m. Values of mixed layer depth were concluded to be accurate to within 2m. Vertical velocities, calculated first by assuming zero horizontal temperature advection in the material derivative equation and second by finding the mass transport necessary to balance the heat budget, show that in the upper 500m of the water column downward vertical motion of lm/hr or less prevailed during storm approach, followed by upward vertical velocity as great as 5.35m/hr during the 12 hr immediately following hurricane passage followed by downward vertical velocity during the large thermocline oscillations.