Mixed layer depth parameterization and ocean surface cooling induced by tropical cyclones

Abstract

Cooling of the ocean surface, induced by the tropical cyclone (TC), provides strong negative feedback leading to TC weakening. Parameterization of the upper ocean mixed layer (ML) depth and the sea surface temperature (SST) anomalies induced by TC is a key issue which is addressed in this paper. Using the one-dimensional heat balance equation and pre-storm vertical profiles of temperature, ML depths are estimated from SST anomalies observed by satellites in wakes of 417 TCs in different regions the World Ocean. To analyze the data, a self-similar approach is used that relates the ML depth to the ML transport and the buoyancy drop at the base of the ML. Expressing the ML wind drift transport in terms of TC parameters (maximum wind speed, translation speed and radius), the Coriolis parameter and underlying stratification, and also taking into account the influence of TC-induced upwelling, a parameterization of the ML depth is proposed, which is quite general. This parameterization combined with the heat conservation equation constitutes parameterization of the SST anomaly induced by the TC. Comparison with observations demonstrates effectiveness of the suggested parameterization in reproducing the SST anomalies in a wide range of surface cooling values (up to −10 °C) produced by TCs of different categories moving across various basins of the World Ocean with different stratification.