Processes that influence sea surface temperature and ocean mixed layer depth variability in a coupled model

A 50-year coupled atmosphere-ocean model integration is used to study sea s urface temperature (SST) and mixed layer depth (h), and the processes which influence them. The model consists of an atmospheric general circulation m odel coupled to an ocean mixed layer model in ice-free regions. The midlati tude SST variability is simulated fairly well, although the maximum varianc e is underestimated and located farther south than observed. The model is c learly deficient in the vicinity of the Gulf Stream and in the eastern trop ical Pacific where advective processes are important. The model generally r eproduces the observed structure of the mean h in both March and September but underestimates it in the North Atlantic during winter. The net surface heat flux strongly regulates both the mean ((-)) and the anomalous (') SSTs throughout the year. The entrainment heat flux, which is proportional to t he product of the entrainment rate (W-e) and the temperature jump at the ba se of the mixed layer (Delta T), influences SSTs in summer and fall, especi ally north of similar to 35 degrees N (45 degrees N) in the Pacific (Atlant ic). W(e)Delta T is more important for the development of SST' in fall comp ared to W(e)Delta T, which is larger in summer. The entrainment rate is dom inated by wind-induced mixing in summer and surface buoyancy forcing in win ter; the density jump at the base of the mixed layer is of secondary import ance. In addition, anomalies in h have a significant impact on the heat bal ance of the mixed layer during spring and summer. Deep winter mixed layers and the storage of thermal anomalies beneath the shallow mixed layer in sum mer leads to large winter-to-winter persistence of SST anomalies in the far North Atlantic, in accord with observations and stochastic climate theory.