Water mass transformation following instability in the mixed layer of the East Greenland Current

Abstract

Observations show that strong southerly winds over the Irminger Sea can excite symmetric instability in the East Greenland Current, resulting in the generation of a low potential vorticity layer below the convectively mixed layer (Le Bras et al., 2022). The role of these downfront wind events on the formation of dense waters is not yet well understood.Using an ensemble of ultra-high resolution models (25 m in the horizontal)  we show that the low potential vorticity layer is virtually indistinguishable from the convectively mixed layer, implying the absence of symmetric instability in coarse models may lead to underestimates in the mixed layer depth and baroclinicity of the East Greenland Current. We explore the hypothesis that symmetric instability acts as the short time-scale response of the current to these southerly wind events and pre-conditions the mixed layer, making it more susceptible to baroclinic instability over longer time-scales. We then investigate whether baroclinic eddy activity is enhanced following these wind events and examine the implications of this on lateral and diapycnal mixing, including by calculating water mass transformation rates.