The Gulf Stream
This page is kept for historical interest, see the
Gulf Stream example for up-to-date code and results.
The setup is as close as possible to that used by Hurlburt & Hogan, 2000 but uses the layered solver described in Popinet, 2020.
See Hurlburt & Hogan, 2000 for details but the main characteristics of the setup are:
- 5 isopycnal layers (see Table 2 of H&H, 2000 for the reference densities, thicknesses etc.)
- Wind stress in the top layer given by the monthly climatology of Hellerman & Rosenstein, 1983
- “Compressed bathymetry” as in H&H, 2000
- Quadratic bottom friction (Cb = 2 x 10-3), Laplacian horizontal viscosity (10 m2/s)
- Atlantic Meridional Overturning Circulation (AMOC) driven by fluxes at the northern and southern boundaries (see Table 2 of H&H, 2000 for the values of fluxes)
Some of the differences below can be due to the longer averages taken in Basilisk (> 10 years versus a few years for H&H, 2000).
Movie and snapshots
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Snapshot of SSH from Hurlburt & Hogan, 2000, fig. 4, 1/32 degree
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Snapshot of SSH, Basilisk, 1/24 degree
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Mean Sea Surface Height (SSH)
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Mean SSH from Hurlburt & Hogan, 2000, fig. 3, 1/32 degree
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Mean SSH, Basilisk, 1/24 degree
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Mean SSH from Hurlburt & Hogan, 2008, fig. 2, 1/32 degree
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Mean SSH, Basilisk, 1/24 degree
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SSH standard deviation
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SSH standard deviationfrom Hurlburt & Hogan, 2000, fig. 9, 1/32 degree
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SSH standard deviation, Basilisk, 1/24 degree
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Surface kinetic energies
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EKE difference from Chassignet & Xu, 2017, fig. 10, 1/50 degree
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EKE difference, Basilisk, 1/24 degree
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The high values in C&X, 2017 may be due to non-converged statistics (i.e. shorter averages in Basilisk show similar features/artefacts).
Field transects
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Zonal velocity at 55W, Basilisk, 1/24 degree, 5 layers
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EKE at 55W, Basilisk, 1/24 degree, 5 layers
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Abyssal currents
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Mean abyssal kinetic energy from H&H, 2000, fig. 11a, 1/32 degree
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Mean abyssal kinetic energy, Basilisk, 1/24 degree
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Mean abyssal layer pressure deviation from H&H, 2000, fig. 10, 1/32 degree
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Mean abyssal layer pressure deviation, Basilisk, 1/24 degree
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Note that there is a factor \rho_0 = 1000 missing in H&H, 2000.
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Abyssal layer EKE from H&H, 2000, fig. 12, 1/32 degree
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Abyssal layer EKE, Basilisk, 1/24 degree
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Abyssal layer mean current from H&H, 2008, fig. 4.a, 1/32 degree
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Abyssal layer mean current, Basilisk, 1/24 degree
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Abyssal layer interface depth from H&H, 2008, fig. 5.d, 1/32 degree
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Abyssal layer interface depth, Basilisk, 1/24 degree
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Top layer
Computational cost etc.
The 1/24 degree domain spans 98W to 14W and 9N to 51N using 2048 \times 1024 grid points. Only five (isopycnal) layers are used in the vertical as in H&H, 2000. The timestep is 150 seconds and the simulation ran for approx 20 years with averages taken after a spinup of 5 years.
The simulation ran at approximately 23 simulated years per day on 2048 cores of the Irene supercomputer at TGCC (i.e. a computational speed close to 109 cells \times timestep / second).
References
[chassignet2017]
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Eric P Chassignet and Xiaobiao Xu. Impact of horizontal resolution (1/12 to 1/50) on Gulf Stream separation, penetration, and variability. Journal of Physical Oceanography, 47(8):1999–2021, 2017. [ DOI ]
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[hurlburt2008]
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Harley E Hurlburt and Patrick J Hogan. The Gulf Stream pathway and the impacts of the eddy-driven abyssal circulation and the Deep Western Boundary Current. Dynamics of Atmospheres and Oceans, 45(3-4):71–101, 2008. [ DOI ]
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[hurlburt2000]
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Harley E Hurlburt and Patrick J Hogan. Impact of 1/8 to 1/64 resolution on Gulf Stream model–data comparisons in basin-scale subtropical Atlantic ocean models. Dynamics of Atmospheres and Oceans, 32(3-4):283–329, 2000. [ DOI ]
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