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| Titel |
Ekman currents and Mixed Layer depth in the North Atlantic subtropical gyre. Observations and Mercator analysis PSY2V4R2-R4. |
| VerfasserIn |
Anna Sommer, Gilles Reverdin, Jacqueline Boutin, Yann Drillet |
| 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 |
250140264
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| Publikation (Nr.) |
 EGU/EGU2017-3628.pdf |
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| Zusammenfassung |
| The study is focused on the ocean currents and was motivated by estimating the role of
Ekman transport in seasonal salinity variability in the North Atlantic subtropical gyre region
of maximum salinity (SSS-max region). Traditionally, one separates in the ‘low frequency
currents’, geostrophic and Ekman components (stationary response to wind stress). The
surface geostrophic part can be estimated from altimetry, and estimates of ‘residuals’
(’Ekman’) are available at 15m from drifts of drogued SVP drifters. However, direct
estimates are usually not available at other depths, and there is an issue with its
vertical structure, and how deep it extends. Thus, we also examined Mercator analysis
PSYV4R2-R4 for the same period and region (August 2012-July 2014). We show
the comparison of average Ekman currents in ML estimated by the widely used
formula τei∗90-
ρfh (where h is MLD) and residual currents (difference between total
current in ML and geostrophic current estimated from SSH) in Mercator analysis
PSYV4R2-R4.
Residual Mercator current averaged in ML is larger than the Ekman current estimated by
the formula, with RMS differences on the order of 0.02 m/s. Part of the difference can be due
to the increments in Mercator data assimilation that we expect to be small at the
weekly time scales that we consider. The differences can also result from Ekman
transport penetrating below MLD (h). The issue might come from MLD not always
coinciding with the Ekman Depth and in the weekly averaging. We also find a difference
in the behavior of the Ekman currents at 15m between drifters and the Mercator
analysis.
Such differences strongly modify how Ekman contributes to advection and salinity
variability in the ML. For example, Ekman advection estimated from Mercator analysis for
the period August 2012-December 2014 in this SSS-max region is -0.88 pss/yr compared to
what we would deduce from observations and the formula τei∗90-
ρfh, which is estimated as -0.17
pss/yr. |
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