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Tidal currents in the northwest African upwelling region

Huthnance, J.M.; Baines, P.G.. 1982 Tidal currents in the northwest African upwelling region. Deep Sea Research Part A. Oceanographic Research Papers, 29 (3). 285-306. 10.1016/0198-0149(82)90097-8

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Abstract/Summary

Tidal currents are analysed from 27 instruments on five moorings having 28 days in common during “Auftrieb '75—Upwelling '75”. The diurnal currents are largely incoherent, probably owing to proximity of the local inertial frequency. The barotropic semi-diurnal currents are modelled by a Kelvin wave propagating northwards with an estimated M2 tidal energy flux of 2 × 1011 W across 23°N. The baroclinic semi-diurnal currents are much less coherent and are strongest at the moorings in 500-m water depth on the steep continental slope, where they are dominated by intermittent near-surface and bottom-intensified motion. These bottom-intesified currents are mostly aligned with the shelf and can only sometimes be modelled as a combination of Rhines' (1970, Geophysical Fluid Dynamics, 1, 273–302) bottom-trapped waves. The bottom currents are also much larger than the 0 (2 cm s−1) estimate for internal tides generated by the onshore component of the barotropic current according to conventional models. We suggest that the strong currents are caused by the stronger longshore component of the barotropic current interacting with longshore topographic irregularities in the shelf and slope. Variability in the basoclinic tide is mainly attributed to changing stratification in the upper 150 m. The M4 harmonic occurs intermittently at 500-m depth on the near-critical continental slope.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1016/0198-0149(82)90097-8
Programmes: POL Programmes
ISSN: 01980149
Date made live: 02 Jul 2013 13:29 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/502506

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