Frontogenesis and variability in Denmark Strait and its influence on overflow water

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Date
2019-07-01
Authors
Spall, Michael A.
Pickart, Robert S.
Lin, Peigen
von Appen, Wilken-Jon
Mastropole, Dana M.
Valdimarsson, Héðinn
Haine, Thomas W. N.
Almansi, Mattia
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DOI
10.1175/JPO-D-19-0053.1
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Keywords
Baroclinic flows
Frontogenesis/frontolysis
Meridional overturning circulation
Ocean dynamics
Topographic effects
Abstract
A high-resolution numerical model, together with in situ and satellite observations, is used to explore the nature and dynamics of the dominant high-frequency (from one day to one week) variability in Denmark Strait. Mooring measurements in the center of the strait reveal that warm water “flooding events” occur, whereby the North Icelandic Irminger Current (NIIC) propagates offshore and advects subtropical-origin water northward through the deepest part of the sill. Two other types of mesoscale processes in Denmark Strait have been described previously in the literature, known as “boluses” and “pulses,” associated with a raising and lowering of the overflow water interface. Our measurements reveal that flooding events occur in conjunction with especially pronounced pulses. The model indicates that the NIIC hydrographic front is maintained by a balance between frontogenesis by the large-scale flow and frontolysis by baroclinic instability. Specifically, the temperature and salinity tendency equations demonstrate that the eddies act to relax the front, while the mean flow acts to sharpen it. Furthermore, the model reveals that the two dense water processes—boluses and pulses (and hence flooding events)—are dynamically related to each other and tied to the meandering of the hydrographic front in the strait. Our study thus provides a general framework for interpreting the short-time-scale variability of Denmark Strait Overflow Water entering the Irminger Sea.
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Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(7), (2019): 1889-1904, doi:10.1175/JPO-D-19-0053.1.
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Spall, M. A., Pickart, R. S., Lin, P., von Appen, W., Mastropole, D., Valdimarsson, H., Haine, T. W. N., & Almansi, M. (2019). Frontogenesis and variability in Denmark Strait and its influence on overflow water. Journal of Physical Oceanography, 49(7), 1889-1904.
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