Submesoscale Vorticity and Divergence in the Alboran Sea: Scale and Depth Dependence

Giovanni Esposito, Maristella Berta, Luca Centurioni, T. M.Shaun Johnston, John Lodise, Tamay Özgökmen, Pierre Marie Poulain, Annalisa Griffa

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

The statistics of submesoscale divergence and vorticity (kinematic properties, KPs) in the Alboran Sea (Mediterranean Sea) are investigated, using data from drifters released during two experiments in June 2018 and April 2019 in the framework of the Coherent Lagrangian Pathways from the Surface Ocean to Interior (CALYPSO) project. Surface drifters sampling the first meter of water (CARTHE and CODE) and 15 m drifters (SVP) are considered. The area of interest is dominated by processes of strong frontogenesis and eddy formation as well as mixing, related to the high lateral gradients between Mediterranean and Atlantic waters. Drifter coverage and distribution allow to investigate the dependence of KPs on horizontal scales in a range between 1 and 16 km, that effectively bridges submesoscale and mesoscale processes, and at two depths, of 1 and 15 m. For both experiments, the surface flow is highly ageostrophic at 1 km scale, with positive vorticity skewness indicating the presence of submesoscale features. Surface divergence quickly decreases at increasing scales with a slope compatible with a turbulent process with broadband wavenumber spectrum, suggesting the influence of surface boundary layer processes such as wind effects, waves and Langmuir cells at the smaller scales. Vorticity, on the other hand, has a significantly slower decay, suggesting interaction between submesoscale and mesoscale dynamics. Results at 15 m are characterized by reduced ageostrophic dynamics with respect to the surface, especially for divergence. Submesoscale processes are present but appear attenuated in terms of KP magnitude and skewness. The results are generally consistent for the two experiments, despite the observed differences in the mixed layer stratification, suggesting that submesoscale instabilities occur mostly at surface fronts associated with filaments of Atlantic and Mediterranean waters that are present in both cases. The results are compared with previous literature results in other parts of the world ocean and a synthesis is provided. Good agreement with previous surface results is found, suggesting some general properties for divergence and vorticity scale dependence. The importance of further investigating very high resolution frontal processes at scales of tens of meters, as well as processes of interaction with high wind effects is highlighted.

Original languageEnglish (US)
Article number678304
JournalFrontiers in Marine Science
Volume8
DOIs
StatePublished - Jul 22 2021

Keywords

  • Alboran sea
  • divergence
  • drifter triplets
  • fronts
  • kinematic properties
  • scale/depth dependence
  • submesoscales
  • vorticity

ASJC Scopus subject areas

  • Oceanography
  • Global and Planetary Change
  • Aquatic Science
  • Water Science and Technology
  • Environmental Science (miscellaneous)
  • Ocean Engineering

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