No abstract

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.

From the analysis of thermistor chain data recorded in a small clongatcd lake, compared with the results of numerical simulations, second vertical modes of the internal scichcs are shown to be active during more than twothirds of the whole stratifcd period, although no rcsonancc with the wind is observed. On the other hand, due to the wind pattern, transversal seiches (mainly the first vertical mode) are also usually excited and they somctimcs dominate. At the end of the stratified period, however, when the thermocline is very sharp, first vertical modeslongitudinal and transversal-are the only ones that are excited. Finally, due to the wind, a forced oscillation of the whole lake is excited.

[1] Microstructure measurements of a triple-diffusive staircase with a stability ratio of 1.1 are presented. Data were recorded at Lake Banyoles, a small lake in Catalonia, Spain, with a warm, salty, and turbid underground inflow. Turbulent scales are well resolved in the two observed convective layers and allow determination of the dissipation rates of the turbulent kinetic energy, e, and of the turbulent temperature fluctuations, c, which are found to be 3.3 Â 10 À7 C 2 /s and 2.7 Â 10 À9 W/kg for one of the layers and 5.9 Â 10 À7 C 2 /s and 3.8 Â 10 À9 W/kg for the other. Thermal spectra for the convective layers look universal in viscous-diffusive and viscous-convective subranges. Characteristic vertical displacements within convective layers could also be obtained on the basis of Thorpe scales and were found to be 0.3 times the layer thickness. Vertical convective fluctuations were estimated and found to be of the order of 10 À4 m/s. When turbulent fluxes were determined within the convective layers on the basis of microstructure data and compared to those at the diffusive interfaces, they showed a stationary state with a mean thermal flux of 3.5 Â 10 À6 C m/s. A comparison of experimental heat fluxes to different models favors the scaling model of Grossman and Lohse (2000) for RayleighBénard convection and the double-diffusive convection model of Fernando (1979aFernando ( , 1979b for low stability. If the 4/3 power law is assumed, then the parameterization proposed by Taylor (1988) for diffusive interfaces at low values of the density ratio is also in accordance with our data.Citation: Sánchez, X., and E. Roget (2007), Microstructure measurements and heat flux calculations of a triple-diffusive process in a lake within the diffusive layer convection regime,