Gulf Stream Transport and Mixing Processes via Coherent Structure Dynamics

Yi Liu, Chris Wilson, Melissa A. Green, Chris W. Hughes

Research output: Contribution to journalArticlepeer-review

Abstract

The Gulf Stream has been characterized as either a barrier or blender to fluid transfer, a duality relevant to gyre-scale climate adjustment. However, previous characterization depended on relatively sparse, Lagrangian in situ observations. The finite-time Lyapunov exponent (FTLE) is calculated from satellite altimetry to identify Lagrangian coherent structures (LCS) in the Gulf Stream region. These LCS provide dense sampling of flow and capture distinct regions associated with mixing. Independent observations of ocean color contain similar flow-dependent structures, providing verification of the method and highlighting transport and mixing processes that influence sea surface temperature and chlorophyll, among other water properties. Diagnosed LCS support the existing Bower kinematic model of the Gulf Stream, but also highlight novel behavior of comparable importance. These include vortex pinch-off and formation of spiral eddies, clearly identified by LCS and which may be explained by considering changes to flow topology and the dynamics of shear-flow instability at both small and large Rossby number. Such processes, seen though LCS, may further enable validation of climate models. The spatial distribution of these intermittent processes is characterized in terms of the criticality of jet dynamics with respect to Rossby wave propagation, and whether the jet is in an unstable or wave-maker regime. The generation and connectivity of hyperbolic trajectories in the flow appears to play an important role in governing large-scale transport and mixing across the Gulf Stream.

Original languageEnglish (US)
Pages (from-to)3014-3037
Number of pages24
JournalJournal of Geophysical Research: Oceans
Volume123
Issue number4
DOIs
StatePublished - Apr 2018
Externally publishedYes

Bibliographical note

Funding Information:
The altimeter products were produced by SSALTO/DUACS and distributed by AVISO, with support from CNES (http://www.aviso.altimetry.fr/duacs). The FTLE diagnosed in this study from this altimeter data are available from doi:10.5281/zenodo.1145909 (pFTLE) and doi:10.5281/zenodo.1145850 (nFTLE). We thank Norman Kuring for creating the original MODIS SST and Chl images that we adapted. CW is supported by the UK Natural Environment Research Council and the UK-OSNAP project (NE/K010875/1). We also thank the Syracuse University OrangeGrid, supported by National Science Foundation (NSF) award ACI-1341006, for providing computational resources. We are grateful to two anonymous reviewers for their constructive comments, which strengthened this paper. Thanks also to J?el Hirschi for discussion on the relative contribution to the MOC east of the Gulf Stream.

Funding Information:
The altimeter products were produced by SSALTO/DUACS and distributed by AVISO, with support from CNES (http:// www.aviso.altimetry.fr/duacs). The FTLE diagnosed in this study from this altimeter data are available from doi:10.5281/zenodo.1145909 (pFTLE) and doi:10.5281/zenodo.1145850 (nFTLE). We thank Norman Kuring for creating the original MODIS SST and Chl images that we adapted. CW is supported by the UK Natural Environment Research Council and the UK-OSNAP project (NE/K010875/1). We also thank the Syracuse University OrangeGrid, supported by National Science Foundation (NSF) award ACI- 1341006, for providing computational resources. We are grateful to two anonymous reviewers for their constructive comments, which strengthened this paper. Thanks also to Jo€el Hirschi for discussion on the relative contribution to the MOC east of the Gulf Stream.

Publisher Copyright:
© 2018. American Geophysical Union. All Rights Reserved.

Keywords

  • Gulf Stream
  • Lagrangian coherent structure
  • mixing
  • satellite altimetry
  • spiral eddies
  • transport barrier

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