The Response of the Ocean to Short-Term Cooling

The role of the ocean in modulating the relaxation of the climate system to short-term, global radiative cooling is explored using a ocean general circulation model. The rate at which SST is damped backed to a background state depends on both atmospheric and oceanic processes; the former is prescribed as simple relaxation of SST, whereas the latter is resolved in the ocean model. In a series of different simulations, we are able quantify the importance of diapycnal mixing, background circulation, and anomalous circulation in transmission of the cooling signal below the mixed layer. Results are shown to be readily interpreted using a simple, analytical two-layer ocean model. We find that oceanic processes play a larger role that atmospheric feedbacks in relaxation back to equilibrium, with ocean mixing the dominant process. Ocean dynamics and climate feedbacks however play a comparable role. Finally, we compare our simple model results with observed cooling due to volcanic eruptions, to assess how well such events can be used to constrain transient climate response.