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| Titel |
Dynamics of a vertical turbulent plume in a stratification typical of Greenland fjords: an idealized model of subglacial discharge |
| VerfasserIn |
Erik Stenberg, Ekaterina Ezhova, Claudia Cenedese, Luca Brandt |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148244
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| Publikation (Nr.) |
 EGU/EGU2017-12482.pdf |
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| Zusammenfassung |
| We the report results of large eddy simulations of a turbulent buoyant plume in a
configuration providing an idealized model of subglacial discharge from a submarine glacier
in stratifications typical of Greenland Fjords. We neglect a horizontal momentum of the
plume and assume that its influence on the plume dynamics is small and important only
close to the source. Moreover, idealized models have considered the plume adjacent
to the glacier as a half-conical plume (e.g., [1]). Thus, to compare the results for
such plume with the classical plume theory, developed for free plumes entraining
ambient fluid from all directions, it is convenient to add the second half-conical part
and consider a free plume with double the total discharge as a model. Given the
estimate of the total subglacial discharge for Helheim Glacier in Sermilik Fjord [2],
we perform simulations with double the total discharge in order to investigate the
dynamics of the flow in typical winter and summer stratifications in Greenland fjords
[3].
The plume is discharged from a round source of various diameters. In winter, when the
stratification is similar to an idealised two-layers case, turbulent entrainment and generation
of internal waves by the plume top are in agreement with the theoretical and numerical
results obtained for turbulent jets in a two-layer stratification. In summer, instead, the
stratification is more complex and turbulent entrainment is significantly reduced. The
subsurface layer in summer is characterized by a strong density gradient and the
oscillating plume generates non-linear internal waves which are able to mix this layer
even if the plume does not penetrate to the surface. The classical theory for the
integral parameters of a turbulent plume in a homogeneous fluid gives accurate
predictions of the plume parameters in the weakly stratified lower layer up to the
pycnocline.
[1] Mankoff, K. D., F. Straneo, C. Cenedese, S. B. Das, C. D. Richards, and H. Singh,
2016: Structure and dynamics of a subglacial discharge plume in a Greenland Fjord. J.
Geophys. Res., 121, doi:10.1002/2016JC011764.
[2] Sciascia, R., F. Straneo, C. Cenedese, and P. Heimbach, 2013: Seasonal variability of
submarine melt rate and circulation in an East Greenland fjord. J. Geophys. Res., 118,
2492-2506.
[3] Straneo, F., R. Curry, D. Sutherland, G. Hamilton, C. Cenedese, K. Vage, and L.
Stearns, 2011: Impact of fjord dynamics and glacial runoff on the circulation near Helheim
Glacier. Nature Geosci., 4, 322-327. |
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