Editorial Type:
Article
Article Type:
Research Article

Prognostic Modeling Studies of the Keweenaw Current in Lake Superior. Part I: Formation and Evolution

Changsheng Chen Department of Marine Sciences, University of Georgia, Athens, Georgia

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Jianrong Zhu State Key Laboratory for Estuarine and Coastal Research, East China Normal University, Shanghai, China

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Elise Ralph Great Lakes Observatory, University of Minnesota, Duluth, Minnesota

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Sarah A. Green Department of Chemistry, Michigan Technological University, Houghton, Michigan

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Judith Wells Budd Department of Geological Engineering and Sciences, Michigan Technological University, Houghton, Michigan

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Frank Y. Zhang Department of Biology, Kean University, Union, New Jersey

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Print Publication:
01 Feb 2001
DOI:
https://doi.org/10.1175/1520-0485(2001)031<0379:PMSOTK>2.0.CO;2
Page(s):
379–395
Restricted access

Abstract

The formation and evolution of the Keweenaw Current in Lake Superior were examined using a nonorthogonal-coordinate primitive equation numerical model. The model was initialized by the monthly averaged temperaturefield observed in June and September 1973 and run prognostically under different forcing conditions with and without winds. As a Rossby adjustment problem, the model predicted the formation of a well-defined coastal current jet within an inertial period of 16.4 h after the current field adjusted to the initial temperature field. The magnitude and direction of this current jet varied with the cross-shelf temperature gradient and wind velocity. It tended to intensify during northeastward (downwelling favorable) winds, and to lessen, or even reverse, during southwestward to northwestward (upwelling favorable) or southeastward (downwelling favorable) winds. In a case with strong stratification and without external atmospheric forcings, a well-defined clockwise warm-core eddy formed near the northeastern coast of the Keweenaw Peninsula as a result of baroclinic instability. A warm-core eddy was detected recently from satellite surface temperature images, the shape and location of which were very similar to those of the model-predicted eddy. The energy budget analysis suggested that the eddy kinetic energy grew exponentially over a timescale of 7 days. Growth was due to a rapid energy transfer from available eddy potential energy. The subsequent decline of the eddy kinetic energy was the result of turbulent diffusion, transfer from the eddy kinetic energy to mean kinetic energy, and outward net energy flux.

Corresponding author address: Dr. Changsheng Chen, Dept. of Marine Sciences, University of Georgia, Athens, GA 30602.

Abstract

The formation and evolution of the Keweenaw Current in Lake Superior were examined using a nonorthogonal-coordinate primitive equation numerical model. The model was initialized by the monthly averaged temperaturefield observed in June and September 1973 and run prognostically under different forcing conditions with and without winds. As a Rossby adjustment problem, the model predicted the formation of a well-defined coastal current jet within an inertial period of 16.4 h after the current field adjusted to the initial temperature field. The magnitude and direction of this current jet varied with the cross-shelf temperature gradient and wind velocity. It tended to intensify during northeastward (downwelling favorable) winds, and to lessen, or even reverse, during southwestward to northwestward (upwelling favorable) or southeastward (downwelling favorable) winds. In a case with strong stratification and without external atmospheric forcings, a well-defined clockwise warm-core eddy formed near the northeastern coast of the Keweenaw Peninsula as a result of baroclinic instability. A warm-core eddy was detected recently from satellite surface temperature images, the shape and location of which were very similar to those of the model-predicted eddy. The energy budget analysis suggested that the eddy kinetic energy grew exponentially over a timescale of 7 days. Growth was due to a rapid energy transfer from available eddy potential energy. The subsequent decline of the eddy kinetic energy was the result of turbulent diffusion, transfer from the eddy kinetic energy to mean kinetic energy, and outward net energy flux.

Corresponding author address: Dr. Changsheng Chen, Dept. of Marine Sciences, University of Georgia, Athens, GA 30602.

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Journal of Physical Oceanography

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