Institut für Ostseeforschung Warnemünde
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TRR181 Energy transfer in atmosphere and ocean, subproject T2: Energy budget of the ocean surface mixed layer

Submesoscale Frontal Instability and Turbulence

contact person: Jen-Ping Peng (jen-nullping.peng@io-warnemuende.de)

Theory and numerical simulations suggest that submesoscale fronts and filaments are subject to various types of instabilities, providing a potentially important pathway for the downscale transport and dissipation of mesoscale kinetic energy in the ocean. This research discusses the real-ocean relevance of these recent concepts based on high-resolution turbulence microstructure and near-surface velocity data from transient submesoscale upwelling filaments in the Benguela upwelling system (South-East Atlantic).

The focus of this study is a sharp submesoscale front located at the edge of the filaments, characterized by persistent downfront winds, a strong frontal jet, and vigorous turbulence under conditions with a steady destabilizing buoyancy forcing. The analysis reveals three distinct frontal stability regimes: (i) forced symmetric instability (FSI) on the light side of the front; (ii) inertial/symmetric instability (ISI) on the anticyclonic side of the front; (iii) marginal shear instability on the cyclonic side of the front, as summarized in the figure below. The data in this study provide direct evidence for the relevance of FSI, ISI, and marginal shear instability for overall kinetic energy dissipation in submesoscale fronts and filaments (see Peng et al., 2020 for more details, doi: https://doi.org/10.1175/JPO-D-19-0270.1)

tl_files/staff/peng/Fig11.png
Sketch of the submesoscale frontal structure and frontal instabilities at the edge of a dense upwelling filament. Figure taken from the PhD thesis of Peng (2020).