Hurricane-ocean interactions during warm climates

Small-scale mixing plays a significant role in large-scale ocean circulation problems, and modeling studies have confirmed a great sensitivity to the magnitude of the vertical or diapycnal diffusivity. But unlike the homogeneous mixing imposed in most models, real ocean mixing varies considerably in space and time; scant attention has been paid to how such variability affects the larger scales. Recent measurements from the eastern Pacific have shown that tropical, upper-ocean mixing may be highly nonlinear, responding most significantly to the strongest blasts of wind.

This talk will review the sensitivity of the large-scale circulations and heat flux to mixing in the upper tropical oceans and explore the implications for hurricane-induced mixing during warm climates such as the Late Cretaceous and Eocene epochs.

I estimate the temporal and spatial mean value of mixing provided by tropical cyclones around the globe, and apply it in a coupled atmosphere-ocean model. The magnitude of the oceans' heat flux and the latitudes at which the ocean makes an important contribution to the total meridional transport of heat increase in warmer climates.

In additional experiments, mixing varies inversely with stratification. This holds the energy available to mixing constant with climate, rather than the diffusivity itself. While the abyssal circulation can be strongly modulated by such a parameterization, the heat flux is less strongly affected.

Finally, I combine these parameterizations to test a more realistic dependence of mixing on tropical climate. The diapycnal diffusivity varies inversely with stratification, but the amplitude is modified in the upper tropical oceans based on the depth to which tropical cyclones directly mix. The cumulative effects of tropical cyclone mixing could make a modest contribution to the oceans' heat flux in the present climate, and could have made a more substantial one during the warmer ones in the geologic past.