On the structure of the Lofoten Basin Eddy

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A small anticyclonic eddy of extraordinary intensity sits in the center of the Lofoten Basin near 69°40′N, 3°E. This paper gives a first detailed description of its kinematics and lowest-order dynamic balances. Using a 75 kHz vessel-mounted acoustic Doppler current profiler, hydrography, and six RAFOS floats to probe the eddy, we document a solid body core with 7-8 km radius and relative vorticity very close to -f, where f is the local Coriolis parameter. Maximum orbital velocities close to 0.8 ms-1 were observed at 18 km radius. One float, trapped in the core of the eddy for 9 months, indicated undiminished strength throughout that period, possibly even intensifying in winter. Hydrography revealed adiabatic conditions from the bottom of a shallow seasonal thermocline to 1000 m depth in early July 2010. Thermal convection in winter maintains an already deep pycnostad, and may also play a key role in intensifying the eddy, quite possibly through penetrative convection that deepens and sharpens the underlying pycnocline. Heat lost to the atmosphere has to be replenished from warm anticyclonic eddies shed off the eastern branch of the Norwegian Atlantic Current, but the mechanism(s) by which it is added to the eddy remains to be studied. Examination of historical data sets suggests the eddy is a permanent feature of the Lofoten Basin. Two hydrocasts from the 1960s also show a similar adiabatic mixed layer albeit 1°C cooler than in 2010, perhaps reflecting the generally cold winter conditions that prevailed then. © 2013. American Geophysical Union. All Rights Reserved.

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Journal of Geophysical Research: Oceans