|Title||Estimating the mean diapycnal mixing using a finescale strain parameterization|
|Publication Type||Journal Article|
|Year of Publication||2015|
|Authors||Whalen C.B, MacKinnon JA, Talley LD, Waterhouse A.F|
|Journal||Journal of Physical Oceanography|
|Type of Article||Article|
|Keywords||abyssal ocean; fine-structure; hawaiian ridge; internal gravity-waves; kinetic-energy; rough topography; southern-ocean; spatial; statistical description; turbulent dissipation; variability|
Finescale methods are currently being applied to estimate the mean turbulent dissipation rate and diffusivity on regional and global scales. This study evaluates finescale estimates derived from isopycnal strain by comparing them with average microstructure profiles from six diverse environments including the equator, above ridges, near seamounts, and in strong currents. The finescale strain estimates are derived from at least 10 nearby Argo profiles (generally <60 km distant) with no temporal restrictions, including measurements separated by seasons or decades. The absence of temporal limits is reasonable in these cases, since the authors find the dissipation rate is steady over seasonal time scales at the latitudes being considered (0 degrees-30 degrees and 40 degrees-50 degrees). In contrast, a seasonal cycle of a factor of 2-5 in the upper 1000m is found under storm tracks (30 degrees-40 degrees) in both hemispheres. Agreement between the mean dissipation rate calculated using Argo profiles and mean from microstructure profiles is within a factor of 2-3 for 96% of the comparisons. This is both congruous with the physical scaling underlying the finescale parameterization and indicates that the method is effective for estimating the regional mean dissipation rates in the open ocean.
There are three main conclusions that arise from this study:
- First, the assumed fundamental physics behind the finescale parameterizations is consistent with our observations over a wide range of internal wave environments. Specifically, our findings are compatible with the notion that the majority of the turbulent energy dissipation in the open ocean is caused by internal waves transferring their energy to smaller scales through non-linear interactions.
- Second, the mean dissipation rate is generally steady in the upper ocean over monthly to seasonal time scales. One notable exception to this is a significant seasonal cycle beneath storm tracks.
- Finally, the finescale strain parameterization is an effective tool for estimating the mean dissipation rate and diffusivity in the open ocean, provided that appropriate averaging is done over the internal wave field environment of interest.