Quantifying Residual, Eddy, and Mean Flow Effects on Mixing in an Idealized Circumpolar Current

Title Quantifying Residual, Eddy, and Mean Flow Effects on Mixing in an Idealized Circumpolar Current
Publication TypeJournal Article
Year of Publication2017
Authors
JournalJournal of Physical Oceanography
Volume47
Number8
Pages1897-1920
Date Published07/2017
Abstract

Meridional diffusivity is assessed for a baroclinically unstable jet in a high-latitude idealized circumpolar current (ICC) using the Model for Prediction across Scales Ocean (MPAS-O) and the online Lagrangian in Situ Global High-Performance Particle Tracking (LIGHT) diagnostic via space–time dispersion of particle clusters over 120 monthly realizations of O(10^6) particles on 11 potential density surfaces. Diffusivity in the jet reaches values of O(6000) m^2/s and is largest near the critical layer supporting mixing suppression and critical layer theory. Values in the vicinity of the shelf break are suppressed to O(100) m^2/s because of the presence of westward slope front currents. Diffusivity attenuates less rapidly with depth in the jet than both eddy velocity and kinetic energy scalings would suggest. Removal of the mean flow via high-pass filtering shifts the nonlinear parameter (ratio of the eddy velocity to eddy phase speed) into the linear wave regime by increasing the eddy phase speed via the depth-mean flow. Low-pass filtering, in contrast, quantifies the effect of mean shear. Diffusivity is decomposed into mean flow shear, linear waves, and the residual nonhomogeneous turbulence components, where turbulence dominates and eddy-produced filamentation strained by background mean shear enhances mixing, accounting for ≥80% of the total diffusivity relative to mean shear [O(100) m^2/s], linear waves [O(1000) m^2/s], and undecomposed full diffusivity [O(6000) m^2/s]. Diffusivity parameterizations accounting for both the nonhomogeneous turbulence residual and depth variability are needed.

URLhttp://journals.ametsoc.org/doi/full/10.1175/JPO-D-16-0101.1
DOI10.1175/JPO-D-16-0101.1
Funding Program: 
Journal: Journal of Physical Oceanography
Number: 8
Volume: 47

Meridional diffusivity is assessed for a baroclinically unstable jet in a high-latitude idealized circumpolar current (ICC) using the Model for Prediction across Scales Ocean (MPAS-O) and the online Lagrangian in Situ Global High-Performance Particle Tracking (LIGHT) diagnostic via space–time dispersion of particle clusters over 120 monthly realizations of O(10^6) particles on 11 potential density surfaces. Diffusivity in the jet reaches values of O(6000) m^2/s and is largest near the critical layer supporting mixing suppression and critical layer theory. Values in the vicinity of the shelf break are suppressed to O(100) m^2/s because of the presence of westward slope front currents. Diffusivity attenuates less rapidly with depth in the jet than both eddy velocity and kinetic energy scalings would suggest. Removal of the mean flow via high-pass filtering shifts the nonlinear parameter (ratio of the eddy velocity to eddy phase speed) into the linear wave regime by increasing the eddy phase speed via the depth-mean flow. Low-pass filtering, in contrast, quantifies the effect of mean shear. Diffusivity is decomposed into mean flow shear, linear waves, and the residual nonhomogeneous turbulence components, where turbulence dominates and eddy-produced filamentation strained by background mean shear enhances mixing, accounting for ≥80% of the total diffusivity relative to mean shear [O(100) m^2/s], linear waves [O(1000) m^2/s], and undecomposed full diffusivity [O(6000) m^2/s]. Diffusivity parameterizations accounting for both the nonhomogeneous turbulence residual and depth variability are needed.

DOI: 10.1175/JPO-D-16-0101.1
Year of Publication: 2017
Citation: " Quantifying Residual, Eddy, and Mean Flow Effects on Mixing in an Idealized Circumpolar Current." Journal of Physical Oceanography. 2017;47:1897-1920.