Lead convection measured with an autonomous underwater vehicle

The winter Lead Experiment (LeadEx) was conducted during 1992 in the Beaufort Sea. There the Autonomous Conductivity Temperature Vehicle (ACTV) was operated under and around leads. These are the first measurements of this kind. Measurements of temperature, salinity, and turbulence parameters were also made at lead edges with sensors fixed to rigid masts. By combining information from the fixed measurements and the ACTV an inertial dissipation method is used to derive horizontal profiles of salt flux from ACTV salinity measurements. Comparisons also show that turbulent vertical velocity perturbations can be estimated from the vertical motion of the ACTV. With these velocity estimates, horizontal profiles of the turbulent fluxes of heat, w′T′, and salt, w′S′, are also computed directly. Data from a wide (1000-m-wide) lead with rapid ice motion indicate stronger turbulence under the lead than downstream, but the character of the flow is that of a convective boundary layer modified by a change in surface buoyancy flux. The convection is characterized by multiple, intermittent plumes that scale in size with the mixed layer depth. At a medium-sized (100-m-wide) lead with slower ice motion the convective circulation set up by the lead is more apparent. Convective plumes are stronger and more prevalent at the lead edges, particularly the downstream edge. The comparison between the horizontal profiles from the ACTV and time series from fixed sensors suggests that lead convection is a combination of a near surface convective boundary layer and a deeper quasi-stationary convection pattern.

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