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On the Importance of Friction in two Typical Continental Waters: off Oregon and Spanish Sahara

Elsevier B.V.
DOI: 10.1016/s0422-9894(08)70842-0


Abstract The current meter data at various depths near the coasts of Oregon (water depth 100 m) and northwest Africa (water depth ≤ 67.m) have been analyzed. The results have been averaged over about seven day periods, so that stationary Ekman layer-like characteristics could be detected. It has been concluded that the entire water column off Africa is frictional, whereas the Oregon coastal dynamics are not so. This is due to the lower Coriolis parameter, larger friction velocity u, and the much lower stratification off Africa. The horizontal density gradients can explain the observed vertical velocity shears off Oregon, but not off Africa. A typical u near Africa is about 0.8 cm/s, whereas that near Oregon is about 0.3 cm/s. The thickness of the bottom Ekman layer is estimated to be about 60 m off Africa and 12 m off Oregon, whereas the thickness of the logarithmic layer is estimated to be about 9 m off Africa and 2 m off Oregon. Ekman turnings of 25°-40° have been observed off Africa. The upper surface layer data near Oregon display hodographs resembling the classical Ekman spiral, rather than the “slab” type mixed layer.

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