Near surface heat flux measurments with a towed vehicle
Date
1997
Authors
Wolk, Fabian
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Abstract
Simultaneous measurements of vertical velocity fluctuations, w', and temperature fluctuations, T', are obtained using a towed horizontal profiler. The instrument was towed at night in the oceanic boundary layer, between depths of 15 m to 25 m. w' and T' yield a direct measure of the turbulent heat flux, F.
The measurements of w' are significantly influenced by instrument motions and the orbital velocities induced by surface waves. A motion correction algorithm is presented that enables us to resolve length scales up to 50 m. The scales that contribute most significantly to F are about 14 m. The direct estimates are compared to simultaneous estimates, Fl, obtained from measurements of the dissipation rate of turbulent kinetic energy. A mixing efficiency, r 0 , is calculated based on the ratio of the direct to the c-flux estimates. The analysis is done for the stable, neutral, and unstable conditions that were encountered along the tow path. We find that the calculated mixing efficiency is in good agreement with the expected values of f 0 .
The direct heat flux estimates are also interpreted with special attention Langmuir circulation. The presence of the Langmuir cells during the tow was verified from the acoustic backscatter of bubble clouds near the sea surface. I seems that Langmuir circulation is not as efficient in transporting heat vertically through the boundary layer as incoherent turbulence.