Barocoupling of the atmosphere and ocean

Abstract

A stability analysis for a two-layer system with a high density contrast is presented, and applied to a simple model of the coupled ocean-atmosphere which consists of a barotropic atmosphere above an oceanic mixed layer of variable depth. Instability (which we call “barocoupling”), in which a topographic mixed layer Rossby wave is coupled with a divergent barotropic Rossby wave in the atmosphere steered by the wind velocity, occurs for westerly winds above a mixed layer whose depth shallows towards the equator. For the most unstable wave, typical e-folding times are 75 days. Oceanic data indicate that mixed layer depth variability is consistent with a barocoupling response. The implications are that weather patterns have a seasonal memory which results from mixed layer-atmospheric interactions of a few months earlier, particularly in the maritime environment of the southern hemisphere. The significance of barocoupling could be tested using a general circulation model which correctly represents mixed layer dynamics.