Editorial Type:
Article
Article Type:
Research Article

Diagnoses of an Eddy-Resolving Atlantic Ocean Model Simulation in the Vicinity of the Gulf Stream. Part I: Potential Vorticity

Mototaka Nakamura Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

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Yi Chao Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

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Print Publication:
01 Feb 2001
DOI:
https://doi.org/10.1175/1520-0485(2001)031<0353:DOAERA>2.0.CO;2
Page(s):
353–378
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Abstract

Output of an eddy-resolving model of the North Atlantic is diagnosed in the vicinity of the Gulf Stream (GS), using quasigeostrophic potential vorticity (QGPV), Ertel’s potential vorticity (PV), and particle trajectories. Time series of QGPV show strong input of QGPV by the GS in the top 1000 m of the model ocean. Vigorous wave motions are observed in the vicinity of the model GS, mixing QGPV in the region. The time-mean horizontal QGPV structures show qualitative similarity to those of large-scale climatological PV calculated from hydrographic data by Keffer and that of Lozier. The top 1000 m of the model ocean is characterized by a tongue or an elongated island of high mean QGPV along the GS. It is demonstrated that the tongue is a product of strong QGPV input by the GS, vigorous mixing by eddies, and dissipation of QGPV along the path of the GS. At the intermediate depths, 1000–2500 m, a large region of nearly homogenized mean PV or weakly varying mean QGPV is found to the west of the Mid-Atlantic Ridge. It is located undernearth a region of strong near-surface eddy activity and is in qualitative agreement with a deep and large pool of nearly homogenized PV recently found by Lozier. Below the pool of nearly homogenized PV or weakly varying QGPV, the mean PV and QGPV show substantial horizontal gradient and some vertical gradient at deep levels. This structure is in qualitative agreement with results of idealized model experiments and a theory of baroclinic neutrality of the midlatitude atmosphere proposed by Lindzen that may well apply to this oceanic region of strong baroclinic wave activity.

Corresponding author address: Dr. Mototaka Nakamura, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 300-323, 4800 Oak Grove Drive, Pasadena, CA 91109.

Email: moto@pacific.jpl.nasa.gov

Abstract

Output of an eddy-resolving model of the North Atlantic is diagnosed in the vicinity of the Gulf Stream (GS), using quasigeostrophic potential vorticity (QGPV), Ertel’s potential vorticity (PV), and particle trajectories. Time series of QGPV show strong input of QGPV by the GS in the top 1000 m of the model ocean. Vigorous wave motions are observed in the vicinity of the model GS, mixing QGPV in the region. The time-mean horizontal QGPV structures show qualitative similarity to those of large-scale climatological PV calculated from hydrographic data by Keffer and that of Lozier. The top 1000 m of the model ocean is characterized by a tongue or an elongated island of high mean QGPV along the GS. It is demonstrated that the tongue is a product of strong QGPV input by the GS, vigorous mixing by eddies, and dissipation of QGPV along the path of the GS. At the intermediate depths, 1000–2500 m, a large region of nearly homogenized mean PV or weakly varying mean QGPV is found to the west of the Mid-Atlantic Ridge. It is located undernearth a region of strong near-surface eddy activity and is in qualitative agreement with a deep and large pool of nearly homogenized PV recently found by Lozier. Below the pool of nearly homogenized PV or weakly varying QGPV, the mean PV and QGPV show substantial horizontal gradient and some vertical gradient at deep levels. This structure is in qualitative agreement with results of idealized model experiments and a theory of baroclinic neutrality of the midlatitude atmosphere proposed by Lindzen that may well apply to this oceanic region of strong baroclinic wave activity.

Corresponding author address: Dr. Mototaka Nakamura, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 300-323, 4800 Oak Grove Drive, Pasadena, CA 91109.

Email: moto@pacific.jpl.nasa.gov

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