Propagation, Diffusion, and Decay of SST Anomalies beneath an Advective Atmosphere

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Abstract A simple conceptual model is used to illustrate aspects of how the midlatitude atmosphere, in the absence of ocean dynamics, responds to and feeds back on sea surface temperature (SST) anomalies. In the model, a dynamically passive ocean mixed layer of fixed depth exchanges heat with a single-level, energy-balance atmosphere with a constant mean wind, U. The temperatures of the two subsystems, TO and TA, respectively, strive to equilibrate through surface heat exchange, which is parameterized as λ(TO − TA). Atmospheric advection of heat has two important effects on the evolution of SST anomalies. First, the SST anomalies propagate downwind at the speed (cA/cO)U, where cA and cO are the heat capacities of the atmosphere and the oceanic mixed layer, respectively. Second, the damping rate of SST anomalies is scale dependent: the distance an atmospheric column travels before it equilibrates with the ocean through surface heat exchange (UcA/λ) introduces a length scale that discriminates between small...