Mixing in the ocean produced by tropical cyclones

Abstract

Tropical cyclones induce entrainment in the upper ocean, and the associated mixing may cool the sea surface significantly. In this paper, the significance of mixing produced by tropical cyclones in the Atlantic is considered. Observed hydrography and tropical cyclone data are used to force an ocean model, which predicts changes in the temperature field due to wind-generated entrainment. The knowledge of the temperature field is used to translate the mixing into volume flow and heat flux, across isotherms. A calculation of the mean, cross isothermal volume flow produced by Atlantic tropical cyclones is presented. Tropical cyclones mix water in the temperature interval between 18 °C and 29 °C. Below 24 °C, the mixing moves water masses towards increasing temperature, and vice versa above 24 °C. The strength of this flow is about 1 × 10⁶ m³ s^-1. Turbulent heat-transport is associated with the mixing, and the diffusive heat-flux across the 24 °C isotherm is estimated to be 4 × 10¹² W. Feedback between tropical-cyclone activity and the area of surface water warmer than 26.5 °C is discussed. This feedback may attenuate large-scale sea-surface temperature anomalies, and its time-scale is estimated to be about 10 years