Influence of Pacific trade winds on recent changes in SST and ocean heat content: external forcing and internal variability

The tropical Pacific SST warmed at a slower rate in the first decade of the 21st century than previous decades. It has been proposed that increased trade winds associated with a strengthened Walker Circulation may explain such relative SST cooling, via increased upwelling near the surface and heat uptake in the subsurface.

We designed an ensemble of partial coupling experiments using IPSL-CM5A-LR to quantify the influence of the trade winds on ocean heat content and SST, and to compare these impacts to those of external forcing for the recent decades. In the first ensemble, we prescribe the daily surface wind over the tropical Pacific to observed values. In the second ensemble, we apply daily climatological observed surface winds. Both simulations use historical external forcings, and are compared to the fully-coupled historical runs. Both ensembles are also compared with the signature of the internally-generated Interdecadal Pacific Oscillation in the IPSL-CM5A-LR.

We examine the SST responses to the prescribed trade winds, as well the responses of the vertical ocean temperature structure. Furthermore, the heat budgets of the Atlantic, Pacific and Indian Oceans will be studied to follow the heat perturbations due to greenhouse gases emissions. We will compare them to the changes due to observed trade winds, in order to attribute the recent changes observed in the heat content and sea level height.