Oceanic mixed layer feedback and tropical Atlantic variability

Abstract

Models of atmospheric circulation are usually forced by prescribing the sea surface temperature (SST), which is equivalent to assuming an infinite heat capacity for the ocean. This assumption breaks down on timescales of a month or longer, when the finite heat capacity of the oceanic mixed layer allows the SST to respond to atmospheric forcing. Experiments using an atmospheric general circulation model coupled to a slab ocean model demonstrate that this SST feedback can play an important role in tropical Atlantic variability. The amplitude of surface heat flux variability is attenuated by this feedback and the persistence of atmospheric flow anomalies is enhanced. The latter effect could have important implications for atmospheric predictability on monthly to seasonal timescales. The results also show that modeling the spatial variations in mixed layer depth is important for an accurate simulation of SST variability.