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Titel |
In-situ estimate of submesoscale horizontal eddy diffusion coefficients across a front |
VerfasserIn |
Francesco Nencioli, Francesco d'Ovidio, Andrea Doglioli, Anne Petrenko |
Konferenz |
EGU General Assembly 2013
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 15 (2013) |
Datensatznummer |
250079383
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Zusammenfassung |
Fronts, jets and eddies are ubiquitous features of the world oceans, and play a key role in
regulating energy budget, heat transfer, horizontal and vertical transport, and biogeochemical
processes. Although recent advances in computational power have favored the analysis of
mesoscale and submesoscale dynamics from high-resolution numerical simulations, studies
from in-situ observations are still relatively scarce. The small dimensions and short duration
of such structures still pose major challenges for fine-scale dedicated field experiments.
As a consequence, in-situ quantitative estimates of key physical parameters for
high-resolution numerical models, such as horizontal eddy diffusion coefficients, are still
lacking.
The Latex10 campaign (September 1-24, 2010), within the LAgrangian Transport
EXperiment (LATEX), adopted an adaptive sampling strategy that included satellite data,
ship-based current measurements, and iterative Lagrangian drifter releases to successfully
map coherent transport structures in the western Gulf of Lion. Comparisons with AVHRR
imagery evidenced that the detected structures were associated with an intense frontal feature,
originated by the convergence and subsequent stirring of colder coastal waters with warmer
open-sea waters.
We present a method for computing horizontal eddy diffusion coefficients by combining
the stirring rates estimated from the Lagrangian drifter trajectories with the shapes of the
surface temperature and salinity gradient (assumed to be at the equilibrium) from the ship
thermosalinograph. The average value we obtained from various sections across the front is
2.5 m2s-1, with horizontal scales (width of the front) ranging between 0.5 and 2.5
km. This is in line with the values commonly used for high-resolution numerical
simulations. Further field experiment will be required to extend the results to different
ocean regions and regimes, and to thoroughly test the robustness of the equilibrium
hypothesis.
Remote sensed measurements of sea surface temperature and elevation could also be used
to compute fine-scale horizontal eddy diffusion coefficients over larger areas and for different
ocean regions. However, the coarse resolution of current sea surface topography observations,
and their unreliability over coastal regions, represent important limitations for this type of
application. The velocity fields provided by the SWOT mission will allow to retrieve
accurate high-resolution stirring rates across the ocean. Combining these rates with
remote-sensed SST gradients will make possible to extend our analysis and investigate
patterns and variability of submesoscale horizontal eddy diffusion at the global scale. |
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