The structure and atmospheric forcing of the mesoscale velocity field in Fram Strait

Abstract

We consider the connection between the wind field and the mesoscale circulation in the northern Greenland Sea, using over 50 record years of current observations to define the current structure in space and time. We find that east of the East Greenland Polar Front the motion is highly coherent in the vertical and that it scales in the horizontal as the internal Rossby radius. The structure depends very little on frequency. The East Greenland Current is dominated by smaller‐scale phenomena in both space and time, and the kinetic energy is low. The available energy in the wind field may be the largest in the world, especially over the Greenland and Iceland seas. The wind power shows a marked seasonal signal that east of the East Greenland Polar Front is paralleled by a similar signal in the fluctuating kinetic energy of the current, and the former leads the current fluctuations by 1–2 months. The mesoscale motions are probably dominated by nonlinear interactions, and the observed vertical and horizontal structure is in general agreement with predictions of the theory of quasi‐geostrophic turbulence forced by atmospheric fluctuations. We conclude that the majority of the mesoscale fluctuations in Fram Strait east of the East Greenland Polar Front are generated by the wind field. However, with few exceptions, the current field is not coherent with the curl of the wind stress, probably primarily owing to the isolating effect of the rough topography. The extent to which the wind field also generates mesoscale motions in the East Greenland Current is uncertain, although the eddy kinetic energy east of the East Greenland Polar Front is probably sufficient to account for conditions in the East Greenland Current by westward advection of eddies.