| The upper ocean, acting as a thermostat, modulates the thermal and dynamical structures of the overlying atmosphere, and hence plays a vital part in climate. In the tropics, its heat content is strongly affected by tropical cyclones (TCs). Specifically, intense winds associated with TCs generate vigorous vertical mixing, and thereby stir the surface warm water with the colder water beneath and alter the thermal structure of the upper ocean. This produces cold and warm anomalies respectively located in the surface and subsurface layers. Subsequently, the upper ocean tends to restore to its normal state through thermodynamic and dynamic processes. The surface cold anomaly is observed to disappear very quickly. At present, however, it is not clear whether only a thin surface layer is warmed or whether the warming affects a significant water mass, resulting in a net positive heat flux into the ocean. Also, taking into account the fact that TCs extract energy out of the ocean during their passage, it is still not known under what conditions TCs induce a net cooling (as they generally increase the ocean heat loss while they persist) or a net warming (due to decreased heat loss in the following weeks).;Integrating satellite observations and numerical simulations, this thesis seeks to better understand the effect of TCs on the upper-ocean heat content. In the first part, satellite-derived sea surface temperature data are used to characterize the spatial structure and temporal evolution of the TC-induced sea surface cooling. In the second part, we show how the translation speed of a TC strongly affects its intensity by modulating the amplitude of the surface cooling and thus the air-sea heat fluxes. Then, numerical simulations with idealized setups are performed to investigate the restratification process in the upper ocean after the passage of a TC and quantify the relative importance of different physical processes in setting the new equilibrium state. The last part of the thesis, based on a theory relating changes in upper-ocean heat content to changes in sea level, is devoted to estimating the impacts of TCs on the upper-ocean heat content using satellite altimetry data. |
