Kantha, L.H.

As part of the DART06B observational campaign in late August 2006, a microstructure profiler was deployed to make turbulence measurements in the upper layers of the Southern Adriatic Sea. Of the nearly 300 total casts, 163 were made near Station B90, where various moorings were deployed in the 90 m deep water column to measure water column properties and meteorological and surface wave conditions. We were able to measure turbulence properties in the upper layers under a variety of atmospheric forcing conditions that included strong wind forcing, night-time convection, mixed convection and wind forcing, weak wind forcing and strong insolation. The resulting dataset provides a kaleidoscope of turbulence properties and turbulent mixing above, below and in the strong pycnocline present at a depth of 15 to 25 m in the coastal waters of the Southern Adriatic Sea during late summer. A slightly modified scaling of the dissipation rate of turbulence kinetic energy in the mixed layer (ML), based on the observed friction velocity u* and the surface buoyancy flux Jb0, reproduces the measured values reasonably well. In the interior, below the ML, the dissipation rate scales like , where LT is the Thorpe scale and N is the buoyancy frequency. Analysis of velocity and density profile measurements from Station B90 and the nearby station B75 suggest that anticyclonic eddies and near-inertial waves can interact in these coastal waters to produce significant horizontal advective density fluxes in the pycnocline.

During the dedicated sea-truth cruise LIGURE2007, a part of the intensive observational campaign Ligurian Sea Air-Sea Interaction Experiment (LASIE) performed in the eastern Ligurian Sea (Italy) from 16th to 23rd June in 2007, the R/V Urania carried out an intensive microstructure measurement program. Most of these measurements were made between 17th and 20th, in the vicinity of a spar buoy anchored 60 km off the coast in a region with a water column depth of approximately 1500 m; the prevailing light wind conditions and intense solar radiation limited the depth of the upper mixed layer to about 10–15m. We carried out measurements of the structure of the upper water column to a depth exceeding about 200 m. Interestingly, the microstructure measurements revealed multiple layers of relatively elevated dissipation and diffusivity rates around a depth of about 100 m. Since the water column is shown not to be not conducive to double-diffusion, these layered structures must have been produced by small-scale shear due to other processes, such as breaking internal waves. In this paper, we describe the oceanographic conditions prevailing at the time of the measurements, as well as the general turbulent properties in the upper part of the water column. In particular, the layered structures below the mixed layer are discussed in detail, with suggestions as to the likely origin and possible ways of investigating these processes.