Climate impacts of stochastic atmospheric perturbations on the ocean

An Interactive Ensemble (IE) platform was established based on a Standard Coupled (SC) climate model with seven atmosphere-land model realizations coupled to a single ocean model and a single sea ice model. The IE strategy reduces stochastic noise generated by atmospheric dynamics and therefore can be used to estimate the impact of atmospheric perturbations on the ocean. The atmospheric noise reduction shallows the mixed layer, modifies the oceanic upwelling/downwelling, and cools the surface. It is assumed that the deterministic part of the surface cooling is due to the reduced heat capacity of the mixed layer in high latitudes and the changed surface wind curl that causes upwelling/downwelling. The positive albedo feedback is responsible for the polar amplified changes. The weakening of meridional overturning circulation (MOC) further suppresses ocean heat transport to the Northern Hemisphere. The model results suggest that the irregular El Niño Southern Oscillation (ENSO) cycle partly arises from the stochastic perturbation in the atmosphere. Comparison between the IE and the SC simulations also indicates the overestimated atmospheric perturbations in the SC model.