Can mesoscale eddy kinetic energy sources and sinks be inferred from sea
surface height in the Agulhas Current ?
Western boundaries (WB) have been suggested to be hotspots of mesoscale
eddy decay, using an eddy kinetic energy (EKE) flux divergence based on
sea surface height (η). The η-based diagnostic requires approximations,
including the use of geostrophic velocities. Here, we assess to what
extent mesoscale EKE flux divergence can be inferred from η using a
numerical simulation of the Agulhas Current. The EKE flux divergence is
composed of two terms: the eddy-pressure work (linear component) and the
advection of EKE (nonlinear component). Both are mainly positive in the
WB region (net EKE sources). However, it is not reliably accounted by
both η-based diagnostics. The η-based eddy-pressure work has a net
contribution in the WB region of the opposite sign than the true one.
Ageostrophic eddy-pressure work dominates the geostrophic one
(corresponding to a β-contribution). It is explained by mesoscale
eddies’s scale to fall below the scale of ζ/β (ζ: root mean square of
normalized relative vorticity for mesoscale eddies; β: latitudinal
variations of Coriolis parameter). The advection done by geostrophic EKE
flux dominates the EKE flux divergence in the WB region. It results in
the EKE flux divergence to be qualitatively estimable using η (up to 54
% of the net EKE source). Our results in the Agulhas Current show a
mesoscale eddy dynamics in contrast with the decay’s paradigm at western
boundaries. Further analysis in other western boundaries are required to
complete our understanding of mesoscale eddies dynamics.