Kounta L., Capet X., Jouanno Julien, Kolodziejczyk N., Sow B., Gaye A. T. (2018). A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic. Part 1 : the poleward slope currents along West Africa. Ocean Science, 14 (5), p. 971-997. ISSN 1812-0784.
Titre du document
A model perspective on the dynamics of the shadow zone of the eastern tropical North Atlantic. Part 1 : the poleward slope currents along West Africa
Kounta L., Capet X., Jouanno Julien, Kolodziejczyk N., Sow B., Gaye A. T.
Source
Ocean Science, 2018,
14 (5), p. 971-997 ISSN 1812-0784
The West African seaboard is one of the upwelling sectors that has received the least attention, and in situ observations relevant to its dynamics are particularly scarce. The current system in this sector is not well known and understood, e.g., in terms of seasonal variability, across-shore structure, and forcing processes. This knowledge gap is addressed in two studies that analyze the mean seasonal cycle of an eddy-permitting numerical simulation of the tropical Atlantic. Part 1 is concerned with the circulation over the West African continental slope at the southernmost reach of the Canary Current system, between similar to 8 and 20 degrees N. The focus is on the depth range most directly implicated in the wind-driven circulation (offshore and coastal upwellings and Sverdrup transport) located above the potential density sigma(t) = 26.7 kg M-3 in the model (approx. above 250 m of depth). In this sector and for this depth range, the flow is predominantly poleward as a direct consequence of positive wind stress curl forcing, but the degree to which the magnitude of the upper ocean poleward transport reflects Sverdrup theory varies with latitude. The model poleward flow also exhibits a marked semiannual cycle with transport maxima in spring and fall. Dynamical rationalizations of these characteristics are offered in terms of wind forcing of coastal trapped waves and Rossby wave dynamics. Remote forcing by seasonal fluctuations of coastal winds in the Gulf of Guinea plays an instrumental role in the fall intensification of the poleward flow. The spring intensification appears to be related to wind fluctuations taking place at shorter distances north of the Gulf of Guinea entrance and also locally. Rossby wave activity accompanying the semiannual fluctuations of the poleward flow in the coastal waveguide varies greatly with latitude, which in turn exerts a major influence on the vertical structure of the poleward flow. Although the realism of the model West African boundary currents is difficult to determine precisely, the present in-depth investigation provides a renewed framework for future observational programs in the region.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Limnologie physique / Océanographie physique [032]
Description Géographique
ATLANTIQUE NORD ; ZONE TROPICALE ; AFRIQUE DE L'OUEST
