Editorial Type:
Article
Article Type:
Research Article

Submesoscale Dynamics in the Northern Gulf of Mexico. Part I: Regional and Seasonal Characterization and the Role of River Outflow

Roy Barkan Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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James C. McWilliams Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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Alexander F. Shchepetkin Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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M. Jeroen Molemaker Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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Lionel Renault Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California

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Annalisa Bracco School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia

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Jun Choi School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia

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Print Publication:
01 Sep 2017
DOI:
https://doi.org/10.1175/JPO-D-17-0035.1
Page(s):
2325–2346
Restricted access

Abstract

Realistic, submesoscale-resolving numerical simulations are used to characterize the flow’s statistics and the geography of surface submesoscale currents in the northern Gulf of Mexico. This study examines the role of the Mississippi–Atchafalaya River system in driving submesoscale currents during winter and summer, on and off the shelf, by investigating two sets of statistically equilibrated solutions, with and without river forcing. In this paper, the first of three, the authors analyze vorticity ζ, horizontal divergence δ, and available potential energy to eddy kinetic energy conversion and show that river forcing has an important effect on the spatial distribution and magnitudes of submesoscale currents in both seasons. During winter, solutions without river forcing display an increase in seasonal-mean values of ζ, δ and compared to solutions with river forcing, particularly east of the Mississippi River delta and offshore. On the contrary, during summer, seasonal-mean values are larger in solutions with river forcing throughout the entire region. The river effects can be rationalized in terms of scaling arguments that relate submesoscale current magnitudes to the surface boundary layer depth and lateral buoyancy gradients. River outflow enhances submesoscale currents by increasing lateral buoyancy gradients but suppresses them by decreasing the boundary layer depth. A discussion of the submesoscale-generating mechanisms that in each season may determine whether the enhancement effect overcomes the suppression effect or vice versa is presented. Regional comparisons of horizontal velocity spectra, root-mean-square ζ, root-mean-square δ, and root‐mean‐square across different resolutions show no sign of convergence even at 150-m horizontal resolution. This demonstrates the numerical challenge of modeling the full range of submesoscale currents.

Supplemental information related to this paper is available at the Journals Online website: https://doi.org/10.1175/JPO-D-17-0035.s1.

© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Roy Barkan, rbarkan@atmos.ucla.edu

This article has companion articles which can be found at http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-17-0040.1 and http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-17-0036.1

Abstract

Realistic, submesoscale-resolving numerical simulations are used to characterize the flow’s statistics and the geography of surface submesoscale currents in the northern Gulf of Mexico. This study examines the role of the Mississippi–Atchafalaya River system in driving submesoscale currents during winter and summer, on and off the shelf, by investigating two sets of statistically equilibrated solutions, with and without river forcing. In this paper, the first of three, the authors analyze vorticity ζ, horizontal divergence δ, and available potential energy to eddy kinetic energy conversion and show that river forcing has an important effect on the spatial distribution and magnitudes of submesoscale currents in both seasons. During winter, solutions without river forcing display an increase in seasonal-mean values of ζ, δ and compared to solutions with river forcing, particularly east of the Mississippi River delta and offshore. On the contrary, during summer, seasonal-mean values are larger in solutions with river forcing throughout the entire region. The river effects can be rationalized in terms of scaling arguments that relate submesoscale current magnitudes to the surface boundary layer depth and lateral buoyancy gradients. River outflow enhances submesoscale currents by increasing lateral buoyancy gradients but suppresses them by decreasing the boundary layer depth. A discussion of the submesoscale-generating mechanisms that in each season may determine whether the enhancement effect overcomes the suppression effect or vice versa is presented. Regional comparisons of horizontal velocity spectra, root-mean-square ζ, root-mean-square δ, and root‐mean‐square across different resolutions show no sign of convergence even at 150-m horizontal resolution. This demonstrates the numerical challenge of modeling the full range of submesoscale currents.

Supplemental information related to this paper is available at the Journals Online website: https://doi.org/10.1175/JPO-D-17-0035.s1.

© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Roy Barkan, rbarkan@atmos.ucla.edu

This article has companion articles which can be found at http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-17-0040.1 and http://journals.ametsoc.org/doi/abs/10.1175/JPO-D-17-0036.1

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