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| Titel |
Study of the air-sea interactions at the mesoscale: the SEMAPHORE experiment |
| VerfasserIn |
L. Eymard, S. Planton, P. Durand, C. Visage, P. Y. Traon, L. Prieur, A. Weill, D. Hauser, J. Rolland, J. Pelon, F. Baudin, B. Bénech, J. L. Brenguier, G. Caniaux, P. Mey, E. Dombrowski, A. Druilhet, H. Dupuis, B. Ferret, C. Flamant, P. Flamant, F. Hernandez, D. Jourdan, K. Katsaros, D. Lambert, J. M. Lefèvre, P. Borgne, B. Squere, A. Marsoin, H. Roquet, J. Tournadre, V. Trouillet, A. Tychensky, B. Zakardjian |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 14, no. 9 ; Nr. 14, no. 9, S.986-1015 |
| Datensatznummer |
250012419
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| Publikation (Nr.) |
 copernicus.org/angeo-14-986-1996.pdf |
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| Zusammenfassung |
| The SEMAPHORE (Structure des Echanges
Mer-Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche
Expérimentale) experiment has been conducted from June to November 1993 in the
Northeast Atlantic between the Azores and Madeira. It was centered on the study
of the mesoscale ocean circulation and air-sea interactions. The experimental
investigation was achieved at the mesoscale using moorings, floats, and ship
hydrological survey, and at a smaller scale by one dedicated ship, two
instrumented aircraft, and surface drifting buoys, for one and a half month in
October-November (IOP: intense observing period). Observations from
meteorological operational satellites as well as spaceborne microwave sensors
were used in complement. The main studies undertaken concern the mesoscale
ocean, the upper ocean, the atmospheric boundary layer, and the sea surface, and
first results are presented for the various topics. From data analysis and model
simulations, the main characteristics of the ocean circulation were deduced,
showing the close relationship between the Azores front meander and the
occurrence of Mediterranean water lenses (meddies), and the shift between the
Azores current frontal signature at the surface and within the thermocline.
Using drifting buoys and ship data in the upper ocean, the gap between the
scales of the atmospheric forcing and the oceanic variability was made evident.
A 2 °C decrease and a 40-m deepening of the mixed layer were measured within
the IOP, associated with a heating loss of about 100 W m-2. This
evolution was shown to be strongly connected to the occurrence of storms at the
beginning and the end of October. Above the surface, turbulent measurements from
ship and aircraft were analyzed across the surface thermal front, showing a 30%
difference in heat fluxes between both sides during a 4-day period, and the
respective contributions of the wind and the surface temperature were evaluated.
The classical momentum flux bulk parameterization was found to fail in low wind
and unstable conditions. Finally, the sea surface was investigated using
airborne and satellite radars and wave buoys. A wave model, operationally used,
was found to get better results compared with radar and wave-buoy measurements,
when initialized using an improved wind field, obtained by assimilating
satellite and buoy wind data in a meteorological model. A detailed analysis of a
2-day period showed that the swell component, propagating from a far source
area, is underestimated in the wave model. A data base has been created,
containing all experimental measurements. It will allow us to pursue the
interpretation of observations and to test model simulations in the ocean, at
the surface and in the atmospheric boundary layer, and to investigate the
ocean-atmosphere coupling at the local and mesoscales. |
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