A description and analysis of mesoscale variability in the Färoe‐Shetland Channel

Abstract

A large part of the surface inflow to the Nordic Seas coalesces into a narrow slope current in the Färoe‐Shetland Channel, and flows along the Shetland shelf edge with mean speeds of order 0.4 m/s. Observations reveal that the flow is unstable and forms large mesoscale meanders with current speeds of up to 0.9 m/s in a front between two water masses that lies along the channel. The meanders tend to form at two specific locations. Long‐term analyses of drifter and altimeter archive data show hot spots in eddy kinetic energy that are greater than 300 cm2/s, and in surface elevation variance that are nearly 40 cm2. A baroclinic instability analysis suggests that the growth time of the meanders should be a few days, with a separation distance of order 65 km, and that their group velocity could be very close to zero depending on the strength of the southward outflow below 500 m. Thus, unlike their counterparts in the Norwegian Coastal Current, for example, the instabilities do not propagate. Decay of the anticyclonic meanders probably leads to the formation of cyclonic eddies that mix North Atlantic Water and Modified North Atlantic Water (MNAW) and create the more homogeneous forms of Atlantic water that are observed as the water moves northward through the channel and into the Norwegian Sea. Mesoscale driven entrainment may help to draw MNAW into the Färoe‐Shetland Channel from around Färoe.