A sketch of density σt, Richardson number Ri and Austausch coefficient Av as functions of depth.
The data are from the coastal upwelling region off Chile where the Ekman layer ususally is very shallow (about 10 m in this case). The thermocline (pycnocline) is seen between 10 m and 25 m, followed by a more moderate increase in density underneath.
In the absence of current measurements, the Richardson number was calculated (as is often done for the estimation of mixing coefficients) assuming constant current shear; it is thus proportional to the density gradient. The Austausch coefficient is inversely proportional to the Richardson number. Only a density scale is shown; the absolute values of Ri and Av depend on the assumptions relating to current shear.
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