SEASONALITY OF SUBMESOSCALE COHERENT VORTICES IN THE NORTHERN BALTIC PROPER: A MODEL STUDY

Väli G., Zhurbas V.M.

A very high-resolution modelling of the northern Baltic Proper shows that in summer the cyclonic and anticyclonic submesoscale coherent vortices (SCVs) with the extremum of vertical vorticity in the surface layer are formed, while the subsurface anticyclonic SCVs in the shape of convex lenses in the density field prevail over the cyclonic SCVs – concave lenses, with the vertical vorticity extremum in the cold intermediate layer below the seasonal thermocline and above the permanent halocline. In winter the seasonal thermocline and cold intermediate layer are replaced by a relatively deep convectively-mixed layer which makes the formation of subsurface concave cyclonic and convex anticyclonic lenses impossible there. Instead, the winter-time cyclonic SCVs with the vertical vorticity extremum at the surface dominate. The core of winter-time cyclonic SCVs is characterized by a negative temperature anomaly throughout the mixed layer. During its life cycle lasting up to several months and more, the modelled SCVs can repeatedly merge with other SCVs of the same sign of vorticity, and the merger makes the eddy stronger thereby contributing to its longevity.

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