Water column structure and statistics of Denmark Strait Overflow Water cyclones |
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| Institution: | 1. Massachusetts Institute of Technology—Woods Hole Oceanographic Institution Joint Program in Oceanography, Woods Hole, MA, USA;2. Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, MA, USA;3. Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA;1. Institute of Agriculture and Environment, Massey University, Private Bag 11 222, Palmerston North, New Zealand;2. School of Science and Health, The University of Western Sydney, Penrith South DC 1797, New South Wales, Australia;3. Department of Infrastructure Engineering, The University of Melbourne, Melbourne, Victoria 3010, Australia;1. Adam Mickiewicz University Poznan, Institute of Physical Geography, Department of Hydrometry, Dziegielowa Street 27, 61-686 Poznan, Poland;2. Adam Mickiewicz University Poznan, Institute of Geology, Department of Hydrogeology and Water Protection, Makow Polnych Street 16, 61-606 Poznan, Poland;1. Universidad de Vigo, Departamento de Física Aplicada, Campus Lagoas-Marcosende, 36310 Vigo, Spain;2. CSIC Instituto de Investigaciones Marinas, Eduardo Cabello 6, 36208 Vigo, Spain;3. MeteoGalicia, Consellería de Medio Ambiente, Territorio e Infraestruturas, Xunta de Galicia, Roma 6. 15707 Santiago de Compostela, Spain;1. Mechanical Engineering, Brigham Young University, Provo, UT 84602, United States;2. Manufacturing Engineering Technology, Brigham Young University, Provo, UT 84602, United States;3. General Motors R&D Center, Warren, MI 48090, United States |
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| Abstract: | Data from seven moorings deployed across the East Greenland shelfbreak and slope 280 km downstream of Denmark Strait are used to investigate the characteristics and dynamics of Denmark Strait Overflow Water (DSOW) cyclones. On average, a cyclone passes the mooring array every other day near the 900 m isobath, dominating the variability of the boundary current system. There is considerable variation in both the frequency and location of the cyclones on the slope, but no apparent seasonality. Using the year-long data set from September 2007 to October 2008, we construct a composite DSOW cyclone that reveals the average scales of the features. The composite cyclone consists of a lens of dense overflow water on the bottom, up to 300 m thick, with cyclonic flow above the lens. The azimuthal flow is intensified in the middle and upper part of the water column and has the shape of a Gaussian eddy with a peak depth-mean speed of 0.22 m/s at a radius of 7.8 km. The lens is advected by the mean flow of 0.27 m/s and self propagates at 0.45 m/s, consistent with the topographic Rossby wave speed and the Nof speed. The total translation velocity along the East Greenland slope is 0.72 m/s. The self-propagation speed exceeds the cyclonic swirl speed, indicating that the azimuthal flow cannot kinematically trap fluid in the water column above the lens. This implies that the dense water anomaly and the cyclonic swirl velocity are dynamically linked, in line with previous theory. Satellite sea surface temperature (SST) data are investigated to study the surface expression of the cyclones. Disturbances to the SST field are found to propagate less quickly than the in situ DSOW cyclones, raising the possibility that the propagation of the SST signatures is not directly associated with the cyclones. |
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| Keywords: | Denmark Strait overflow water cyclone East Greenland boundary current system East Greenland Spill Jet Deep Western Boundary Current |
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