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Can mesoscale eddy kinetic energy sources and sinks be inferred from sea surface height in the Agulhas Current ?
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  • Pauline Tedesco,
  • Jonathan Gula,
  • Pierrick Penven,
  • Claire Menesguen,
  • Quentin Jamet,
  • Clément Vic
Pauline Tedesco
Imperial College London

Corresponding Author:[email protected]

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Jonathan Gula
Université de Bretagne Occidentale
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Pierrick Penven
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Claire Menesguen
Ifremer - Laboratoire d'Océanographie Physique et Spatiale
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Quentin Jamet
Institut des Géosciences de l'Environnement
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Clément Vic
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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.