No abstract

[1] The dependence of the mixed layer depth h D on the sea surface fluxes is analyzed based on measurements taken along a cross-Atlantic section 53°N. A linear function h D % 0.44L f , where L f = u * /f is the Ekman scale, well represents the influence of the wind stress u * and rotation f on the mixed-layer deepening, thus indicating that the influence of convective mixing in late spring at this latitude is of a lesser importance. Also, data showed reasonable correlation of h D with the stratified Ekman scale L fN = u * / ffiffiffiffiffiffiffiffi fN pc p , where N pc is the buoyancy frequency in the pycnocline, according to h D % 1.9L fN . In both cases the highest correlation between h D and the corresponding lengthscales is achieved when u * values taken 12 hours in advance of the mixed layer measurements were used, which may signify the adjustment time of inertial oscillations to produce critical shear at the base of the mixed layer. The vertical profiles of the dissipation rate e(z) are parameterized by two formulae that are based on the law of the wall scaling e s (z) = u * 3 /0.4z and the buoyancy flux J b : e 1 (z) = 2.6e s (z) + 0.6J b and e 2 (z) = e s (z) e s (z) + 3.7J b . The first parameterization is used to calculate the integrated dissipationẽ int over the mixing layer, which was found to be $3-7% (5% on the average) of the wind work E 10 . The positive correlation between h D andẽ int /E 10 suggests that in deeper quasi-homogeneous layers a larger portion of the wind work is consumed by viscous dissipation vis-à-vis that is used for entrainment. As such, the mixing efficiency, which is based on integral quantities, is expected to decrease with the growth of the mixed layer.

No abstract

No abstract

No abstract