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| Titel |
Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves |
| VerfasserIn |
C. Guiavarch, A. M. Treguier, A. Vangriesheim |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 5, no. 2 ; Nr. 5, no. 2 (2009-05-18), S.141-153 |
| Datensatznummer |
250002419
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| Publikation (Nr.) |
 copernicus.org/os-5-141-2009.pdf |
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| Zusammenfassung |
| In the Gulf of Guinea, intraseasonal variability is large at the equator and
along the coast. Current data on the continental slope near 7.5° S
show very energetic biweekly oscillations at 1300 m depth. A high resolution
primitive equation numerical model demonstrates that this deep variability is
forced by equatorial winds, through the generation of equatorial Yanai waves
that propagate eastward and at depth, and then poleward as coastally-trapped
waves upon reaching the coast of Africa. Intraseasonal variability is
intensified along the coast of the Gulf of Guinea, especially in the 10–20 day
period range and at depths between 500 and 1500 m. The kinetic energy
distribution is well explained at first order by linear theory. Along the
equator, eastward intensification of energy and bottom intensification are in
qualitative agreement with vertically propagating Yanai waves, although the
signal is influenced by the details of the bathymetry. Along the coast,
baroclinic modes 3 to 5 are important close to the equator, and the signal is
dominated by lower vertical modes farther south. Additional current meter
data on the continental slope near 3° N display an energy profile in
the 10–20 day period band that is strikingly different from the one at
7.5° S, with surface intensification rather than bottom
intensification and a secondary maximum near 800 m. The model reproduces
these features and explains them: the surface intensification in the north is
due to the regional wind forcing, and the north-south asymmetry of the deep
signal is due to the presence of the zonal African coast near 5° N. A
4 years time series of current measurements at 7.5° S shows that the
biweekly oscillations are intermittent and vary from year to year. This
intermittency is not well correlated with fluctuations of the equatorial
winds and does not seem to be a simple linear response to the wind forcing. |
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