Impact of Tropical Cyclone Wind Forcing on the Global Climate in a Fully Coupled Climate Model
Tropical cyclones (TCs) alter upper-ocean temperature and influence ocean heat content via enhanced turbulent mixing. A better understanding of the role of TCs within the climate system requires a fully coupled modeling framework, where TC-induced ocean responses feed back to the atmosphere and subsequently to the climate mean state and variability. Here, we investigate the impacts of TC wind forcing on the global ocean and the associated feedbacks within the climate system using the fully coupled Community Earth System Model version 1.3 (CESM1.3). Using the low-resolution version of CESM1.3 (1° atmosphere and ocean grid spacing) with no intrinsic TCs, we conduct a suite of sensitivity experiments by inserting TC winds extracted from a high-resolution (0.25° atmosphere grid spacing) TC-permitting simulation into the low-resolution model. Results from the low-resolution TC experiment are compared to a low-resolution control simulation to diagnose TCs’ impact.
Understanding TCs’ feedbacks to the large-scale climate is important for restricting climate prediction uncertainties across various time scales. We conduct a suite of sensitivity experiments by inserting TC winds extracted from a high-resolution TC-permitting simulation into the low-resolution model. We found that the added TC winds can increase ocean heat content by affecting ocean vertical mixing, air–sea enthalpy fluxes, and cloud amount. The added TCs can influence mean SST, precipitation, ocean subsurface temperature, and ocean mixed layer depth. We found a strengthening of the wind-driven subtropical cells and a weakening of the Atlantic meridional overturning circulation. TCs in the model cause anomalous equatorward ocean heat convergence in the deep tropics and an increase of poleward ocean heat transport out of the subtropics. Our modeling results provide new insights into the multiscale interactions between TCs and the coupled climate system.
Tropical cyclones are expected to change with global warming, but these weather systems can also feed back to their environment, e.g. by strong winds that influence the upper ocean. While this effect has been studied in some ocean simulations, it is not clear to what degree the thus stimulated changes in sea surface temperatures affect the wider climate system. Here, we use a suite of fully coupled global Earth System Model simulations to assess these potential feedbacks. We find that TCs cool the ocean surface and warm the thermocline, linked to an increase in heat uptake. This in turn can influence the oceans' subtropical and subpolar gyres and slightly weakens the Atlantic meridional overturning circulation. These changes shift patterns of oceanic heat transport, which could feed back into the atmosphere. There, we find a shift in precipitation patterns, especially at low latitudes. These findings show that TC winds can change the oceans' surface conditions and circulation globally. Given the expected changes of TCs, these effects should therefore be considered in future climate projections.