Tropical Cyclones' influence on the ocean: from event scale processes to climate scale consequences

Strong winds associated with Tropical Cyclones (TCs) trigger intense mixing in the upper ocean. While the resulting surface cooling feeds back negatively on TCs intensity, the associated sub-surface warming has been suggested to substantially modify the ocean heat budget. A half-degree global ocean model experiment that realistically samples the ocean response to more than 3,000 TCs over the last 30 years is used to investigate the processes induced by TCs at the local scale and their impact on the ocean at the climate scale.

Vertical mixing is the dominant process explaining surface cooling close to the strongest TCs' track. This process has received the largest attention from previous studies investigating the climatic importance of TC-ocean interaction, but surface cooling is increasingly due to heat fluxes as we consider larger space scales. Both heat fluxes and vertical advection induced by TCs also influence the ocean mean state. Vertical mixing does induce an enhanced ocean heat uptake (OHU) consistent with previous estimates. However, two processes have to be taken into account when evaluating the importance of this OHU for climate:
1) about half the ocean heat uptake is in fact used to compensate ocean heat loss by enhanced surface fluxes due to TCs,
2) most of the remaining heat injected into the ocean during TC seasons is re-entrained by the deepening of the mixed layer in fall and winter.
As a consequence of this later point, the main TCs' climatological impact is to reduce the amplitude of surface temperature seasonal cycle more than to modify the ocean heat transport.

references:

Vincent et al. (2012) Processes setting the Characteristics of Sea Surface Cooling induced by Tropical Cyclones. JGR, 117, C02020

Vincent et al. (2012) Influence of Tropical Cyclones on sea surface temperature seasonal cycle and ocean heat transport. Climate Dynamics