Diagnosis of the vertical motions in a mesoscale stirring region

A high-resolution survey was conducted as part of the 2001 Programme Ocean Multidisciplinaire Meso Echelle (POMME 2) experiment in a region of the northeast Atlantic Ocean characterized by a large number of strongly interacting mesoscale eddies. The survey was located between mesoscale eddies in an area where the horizontal stirring processes were dominant. Diagnosis, using SeaSoar data combined with the analysis of altimeter data, reveals an energetic vertical velocity field involving elongated thin structures with alternate signs and amplitude up to 20 m day(-1). The 3D dynamics involved in the appearance of these vertical motions is the restoration of the thermal wind balance within the small-scale density filaments that are elongated by the stirring processes. These experimental results reinforce the conclusions of previous numerical studies pointing out the necessity to explicitly include the effects of the filamentation process in ocean models.