| Outside topographic boundary layers, turbulence and mixing in the ocean is closely related to
breaking internal waves. Over the last two decades it has become common to exploit this
relationship to infer oceanic turbulence and mixing levels from measurements of
internal-wave parameters, such as vertical shear and strain, using a set of methods termed
“finestructure parameterization methods.” Here, we report on a newly discovered relationship
between vertical velocity in the internal-wave band and kinetic energy dissipation due to
turbulence.
Using a set of simultaneous profiles of hydrography, vertical velocity (from LADCP data)
and kinetic-energy dissipation collected in dynamically diverse settings (including the open
ocean, a rift valley on the MAR, Luzon Strait and Drake Passage), at latitudes between 10°
and 75°, and covering a large range of density stratifications, it is shown that vertical-velocity
finestructure is closely correlated with kinetic-energy dissipation. This correlation defines a
new finestructure parameterization method for oceanic turbulence based on internal-wave
vertical-velocity measurements. The available data indicate that the new method yields at
least as good agreement between parameterized and microstructure-derived kinetic
energy dissipation as the most recent of the shear/strain parameterizations, without
requiring any corrections for density stratification, latitude or internal-wave frequency
content.
Since current shear/strain-parameterizations and the new vertical-velocity based
parameterization are sensitive to different parts of the internal-wave frequency band, it is
anticipated that parameterizations based on combined vertical-shear, strain, and
vertical-velocity measurements will be associated with smaller uncertainties than either of the
currently available methods. |