A multifaceted isoneutral eddy transport diagnostic framework and its
application in the Southern Ocean
Abstract
We propose a multifaceted isoneutral eddy transport diagnostic framework
that combines the stationary-transient and Leonard’s decomposition in
large eddy simulation (LES). We diagnose the subfilter flux, the
isotropic transport coefficient, and the anisotropic transport tensor or
eigenvalues in the Southern Ocean (SO). The anisotropic tensor greatly
reduces the reconstruction error of the subfilter flux because of its
ability to distinguish the directionality of dynamic information,
especially the topographic effect. A thorough analysis of the
anisotropic tensor or transport eigenvalues reveals that the sign
combination of the transport eigenvalues of the symmetric tensor links
to the evolution of domainintegral large-scale PV enstrophy and the
combination of different signs is most often, meaning the dominance of
filamentation process in the SO. In the region with intense anisotropy,
the dominant eigenvector tends to be perpendicular to the large-scale PV
gradient, indicating an important role of the PV barrier mechanism in
the SO transport process. The two distinct decompositions leveraged in
our framework generate intriguing and profound results. Under the
stationary-transient decomposition, we find a significant stationary
contribution and the duality of the topographic effect which can not
only anchors stationary structures but also organizes transient motions.
Leonard’s decomposition, allows us to investigate the collective effects
of the standing wave train, cross-scale interaction, and subfilter
eddy-eddy interaction on the filtered space-time scale. We emphasize the
complete subgrid flux, not the mere Reynolds term, and the LES framework
needs to be considered in the subgrid parameterization of the coarse
resolution ocean model.