Modification of ocean eddies by air‐sea interaction

A mixed‐layer model is developed for seasonal time scales and used to investigate the modification of ocean eddies by air‐sea interaction. An eddy is modified by the air‐sea interaction for the local envionment and the feedback from its surface temperature signal, which alters the surface heat and water fluxes. This buoyancy forcing tends to decrease the eddy temperature anomaly, and seasonal changes in mixed‐layer depth lead to the surface signal being removed in summer and reappearing in winter. The dynamical adjustment of the eddy is assessed by coupling the mixed‐layer model to a quasi‐geostrophic model: the buoyancy forcing alters the eddy velocity profile and, over several seasons, may lead to the formation of a subsurface velocity maximum. After the spring decrease in mixed‐layer depth, the eddy potential vorticity anomaly is reduced, and lateral mixing may subsequently play a role in further eroding the eddy. These modelling predictions are supported by the observations of a cold‐core eddy in the seasonal boundary layer of the northeast Atlantic.