DIURNAL RESTRATIFICATION AND TURBULENCE IN THE OCEANIC SURFACE MIXED-LAYER .2. MODELING

We find that daytime restratification of the remnant layer is important to modeling both the decay of convective turbulence during the day and convective deepening the following night, Penetrating solar insolation accounted for about 60% of the observed restratification of the remnant layer. Of the other processes supplying the remaining restratification, we believe lateral advection is the most important and sets a limit on the capabilities of one-dimensional mixed-layer models. In the morning, with the end of convective forcing, there was an initial period lasting nearly an hour, similar to the convective time scale, during which epsilon in the remnant layer remained nearly constant. After that, turbulence in the remnant layer could be modeled in accordance with a balance between epsilon and the storage term for turbulent kinetic energy (TKE). Energy storage is computed using q2 = (epsilonl/C)2/3, where l = 0.84L(O), the Ozmidov scale, matches observed overturning scales during most of the decay. Calculating L(O) for the observed linearly increasing stratification gives a modified exponential form for the decay. A value of C = 0.04 gives the best fit. This decay lasted about 5 hours, until (epsilon) reached almost-equal-to 5 x 10(-10) W kg-1. Then for the remainder of the restratification period, dissipation and production of TKE due to vertical shear appeared to be approaching a balance.