TURBULENCE IN THE STATICALLY UNSTABLE OCEANIC BOUNDARY-LAYER UNDER ARCTIC LEADS

Measurements of turbulent stress, heat flux, salinity flux, and turbul ent kinetic energy (TKE) dissipation were made in the oceanic boundary layer under freezing leads during the 1992 Lead Experiment project in the Arctic Ocean north of Alaska. Results from two instrument systems , one comprising a vertical array of four turbulence-measuring instrum ent clusters, the other an automated, loose-tethered microstructure pr ofiler, show that forcing by modest surface fluxes (surface friction v elocity u(0) similar to 0.7 cm s(-1), surface buoyancy flux (w'b')(0) similar to -0.7 x 10(-7) W kg(-1)) substantially changes the scales a nd character of boundary layer turbulence relative to forcing by stres s alone. Despite continuous freezing at the surface a diurnal cycle of heating and cooling of the mixed layer was seen, with downward oceani c heat flux as high as 70 W m(-2) observed at middepth in the mixed la yer near solar noon. Heat flux was determined both by direct eddy cova riance of temperature and vertical velocity at fixed levels and from T KE and thermal dissipation estimates from the profiling instrument, wi th reasonable agreement. Similarly, there was close correspondence bet ween TKE dissipation estimates obtained from inertial subrange spectra l levels at the fixed instruments and from microstructure shear profil es. TKE production was dominated by buoyancy flux through most of the boundary layer. Thermal and saline eddy diffusivities were computed fr om directly measured fluxes and mixed layer temperature and salinity g radients, with mean values of 0.046 and 0.049 m(2) s(-1) for temperatu re and salinity, respectively. Kolmogorov constants for relating therm al and saline dissipations to inertial subrange spectral levels were f ound to be 0.9 and 1.0, respectively, but with large scatter.