Published in

American Meteorological Society, Journal of Physical Oceanography, 7(43), p. 1525-1532, 2013

DOI: 10.1175/jpo-d-13-059.1

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Observations of Barotropic Oscillations and Their Influence on Mixing in the Faroe Bank Channel Overflow Region

Journal article published in 2013 by Elin Maria K. Darelius ORCID, Jenny E. Ullgren, Ilker Fer
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

Observations of hydrography, currents, and microstructure are presented together with sea surface height (SSH) patterns from concurrent satellite tracks to describe the subinertial oscillations in the region downstream of the Faroe Bank Channel overflow. Energetic oscillations with a dominant 3-5-day period have previously been observed in the dense bottom layer and found to be consistent with topographic Rossby waves. Here, the authors present evidence that the oscillations extend over the whole water column and are connected to a wave-like pattern in SSH along the continental slope. The waves are observed in two satellite tracks running parallel to the slope and indicate a wavelength of 50-75 km, an amplitude of about 5 cm, and a phase speed of 15-20 cm s(-1). The pattern extends at least 450 km along the slope. Repeat occupations of a section through a 4-day period show a barotropic velocity anomaly that is associated with an increase in plume transport [from 0.5 to 2.5 Sv (1 Sv 10(6) m(3) s(-1))] and interface height (from 100 to 200 m) as well as changes in dissipation rates and mixing. Estimates of entrainment velocity w(E) vary with a factor of 10(2) over the oscillation period, and there is an inverse relation between w(E) and plume thickness, that is, mixing is most intense when the dense bottom layer is thin. High values of w(E) coincide with a large percentage of critical Richardson numbers in the interfacial layer. The rotational motion, or the horizontal stirring, is observed to bring water from the south, traceable because of its low oxygen concentrations, into the plume.