Mixing processes near boundaries
Date
2018-11-14
Authors
Colbo, Keir Murray
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Abstract
Using a large eddy simulation (LES) model the cross-cell diffusion of
neutrally buoyant and buoyant particles in Langmuir circulation is studied.
The non-dimensional diffusivity is found to asymptote to a constant value for
sufficiently small Langmuir number. This allows a parameterization for the
cross-cell diffusivity that depends only on well known physical properties
of the wind and wave field. Buoyant particles are found to behave similarly,
but with a substantial reduction of the cross-cell diffusivity.
Lateral Reynolds stresses from an array of acoustic Doppler current profilers
(ADCPs) are computed for fluctuations about a tidal mean. The results
are compared with the observed lateral shear to estimate the horizontal eddy
viscosity, O (10 m2/s). Possible parameterizations of the eddy viscosity are
discussed. The lateral Reynolds stresses acting on the estuarine mean flow
are also calculated.
The velocity data from the ADCPs along with density data from temperature
chain moorings are used to examine the partition of energy between
internal waves and the vortical mode. Consistency relations for the ratio
of counterclockwise to clockwise energy (CCW/CW) and potential to horizontal
kinetic energy (PE/HKE) are modified to account for the effect of
boundaries and Doppler shifting. Exact partitioning of the energy is not
possible, but the signature of both internal waves and vortical modes can be
detected.
Description
Keywords
Waves, Doppler effect, Ocean currents, Measurement