Oceanic Response to Tropical Cyclones

Abstract

In Section 3.1 we discussed the importance of sensible and latent heat addition from the ocean to the atmosphere in maintaining tropical cyclones. But the relationship between the ocean and the atmosphere during hurricane conditions is not a one-way interaction. The stress exerted by strong winds on the surface water and the negative atmospheric pressure anomaly associated with the hurricane both produce accelerations in the ocean and lead to important changes in the ocean circulation. The negative pressure anomaly leads to a rise of mean sea level under the storm of about 1 cm per millibar of pressure drop. This mound of water follows the storm and contributes to the storm surge when the hurricane makes landfall. The strong winds generate surface waves with amplitudes of 20 m or more.⁴ The curl of the stress generates divergence in the upper layer of the ocean, producing regions of upwelling and downwelling. Turbulence is also generated in the ocean by the wind stress and this turbulence mixes warm surface waters with deeper cooler water. The combination of upwelling and vertical mixing typically produces decreases in the surface ocean temperature of 1–3°C and may occasionally produce decreases as large as 5°C (Leipper, 1967; Landis and Leipper, 1968). As suggested by Fisher (1958) these decreases may affect the intensity of slow-moving or stationary storms by reducing evaporation into the atmosphere.