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| Titel |
Fine-resolution altimetry data for a regional application in the Bay of Biscay |
| VerfasserIn |
Renaud Dussurget, Florence Birol, Rosemary A. Morrow |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250048750
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| Zusammenfassung |
| The Bay of Biscay, in the North-East Atlantic, is a complex environment with a chaotic
topography and a wide range of ocean dynamics, including a weak anticyclonic basin-wide
circulation, a coastal poleward current, mesoscale propagating features and also high
frequency shelf dynamics. The region has strong cloud cover, so visible and infra-rouge
satellite observations are sparsely distributed. Satellite altimetry measurements are also
limited near the coasts by missing data, but also by the need for complex coastal dynamic
atmospheric corrections and tidal models. Recent studies have shown that the use of
state-of-the-art de-aliasing models and improved data processing significantly improves the
quality of the data in these highly dynamic regions and enables analysis of finer scale
dynamical processes.
The combined use of altimetric maps and along-track altimeter data is a keypoint of this
study. First, along-track data provide fine scale information about local circulation (ie. at
instrumental resolution), especially in the coastal zone where the slope currents can be
observed using data from the X-TRACK coastal oriented processor. On the other hand,
AVISO gridded data have a coarser resolution (1/3Ë ) but are widely used for mesoscale
studies, as they estimate the sea level variability over 2 dimensions.
A Wavelet Analysis has been applied to the along-track data to assess characteristics of
the mesoscale dynamics at a regional level. This has revealed fine scale dynamics,
with greater occurrences closer to the generation sites. Detected eddies also tend to
increase in diameter and amplitude offshore, suggesting an inverse cascade from
smaller scales to larger scales, in agreement with the 2D geostrophic turbulence
theory.
Inter-comparisons between along-track data and altimetric maps suggested that the latter
is not able to reproduce properly the local dynamical scales, which results in a weaker eddy
field, with geostrophic velocities reduced by a factor of 2, though some evidence of westward
propagation can be observed. Indeed, the mapped and alongtrack spectral slopes
diverge significantly at scales larger than the decorrelation scale used to produce these
maps.
Based on these results, we propose a higher resolution multi-scale Optimal
Interpolation scheme, adapted to the region and its dynamics. This involves applying a
detailed knowledge of the local scales, and how they evolve spatially and temporally,
using observations and/or modelling. Resulting maps allow the investigation of
finer-scale features ( |
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