sandbox/popinet/gulf-stream.md

    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

    Animation of the relative vorticity (approx. 2 years), min and max are \pm 10-4 s-1. The spatial resolution is 1/24 degree.

    Snapshot of SSH from Hurlburt & Hogan, 2000 Snapshot of SSH, Basilisk, 1/24 degree
    Snapshot of SSH from Hurlburt & Hogan, 2000, fig. 4, 1/32 degree
    Snapshot of SSH, Basilisk, 1/24 degree

    Mean Sea Surface Height (SSH)

    Mean SSH from Hurlburt & Hogan, 2000 Mean SSH, Basilisk, 1/24 degree
    Mean SSH from Hurlburt & Hogan, 2000, fig. 3, 1/32 degree
    Mean SSH, Basilisk, 1/24 degree
    Mean SSH from Hurlburt & Hogan, 2008 Mean SSH, Basilisk, 1/24 degree
    Mean SSH from Hurlburt & Hogan, 2008, fig. 2, 1/32 degree
    Mean SSH, Basilisk, 1/24 degree

    SSH standard deviation

    SSH standard deviation from Hurlburt & Hogan, 2000 SSH standard deviation, Basilisk, 1/24 degree
    SSH standard deviationfrom Hurlburt & Hogan, 2000, fig. 9, 1/32 degree
    SSH standard deviation, Basilisk, 1/24 degree
    SSH standard deviation from Chassignet & Xu, 2017, fig. 7

    SSH standard deviation from Chassignet & Xu, 2017, fig. 7

    SSH standard deviation, Basilisk, 1/24 degree

    SSH standard deviation, Basilisk, 1/24 degree

    Surface kinetic energies

    Mean surface kinetic energy from Chassignet & Xu, 2017, fig. 4

    Mean surface kinetic energy from Chassignet & Xu, 2017, fig. 4

    Mean surface kinetic energy, Basilisk, 1/24 degree

    Mean surface kinetic energy, Basilisk, 1/24 degree

    Surface eddy kinetic energy from Chassignet & Xu, 2017, fig. 14

    Surface eddy kinetic energy from Chassignet & Xu, 2017, fig. 14

    Surface eddy kinetic energy, Basilisk, 1/24 degree

    Surface eddy kinetic energy, Basilisk, 1/24 degree

    EKE difference from Chassignet & Xu, 2017, fig. 10, 1/50 degree
    EKE difference, Basilisk, 1/24 degree

    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

    The TOPEX transect from Figure 5 of C&X, 2017

    The “TOPEX” transect from Figure 5 of C&X, 2017

    The Oleander transect from Figure 6 of C&X, 2017

    The “Oleander” transect from Figure 6 of C&X, 2017

    The Oleander transect, Basilisk, 1/24 degree

    The “Oleander” transect, Basilisk, 1/24 degree

    Cross-section at 55W from Figure 15 of C&X, 2017, 32 layers

    Cross-section at 55W from Figure 15 of C&X, 2017, 32 layers

    Zonal velocity at 55W, Basilisk, 1/24 degree, 5 layers
    EKE at 55W, Basilisk, 1/24 degree, 5 layers

    Abyssal currents

    Mean abyssal kinetic energy from H&H, 2000, fig. 11a, 1/32 degree
    Mean abyssal kinetic energy, Basilisk, 1/24 degree
    Mean abyssal layer pressure deviation from H&H, 2000, fig. 10, 1/32 degree
    Mean abyssal layer pressure deviation, Basilisk, 1/24 degree

    Note that there is a factor \rho_0 = 1000 missing in H&H, 2000.

    Abyssal layer EKE from H&H, 2000, fig. 12, 1/32 degree
    Abyssal layer EKE, Basilisk, 1/24 degree
    Abyssal layer mean current from Figure 3 of H&H, 2008, 1/32 degree

    Abyssal layer mean current from Figure 3 of H&H, 2008, 1/32 degree

    Abyssal layer mean current, Basilisk, 1/24 degree

    Abyssal layer mean current, Basilisk, 1/24 degree

    Abyssal layer mean current from H&H, 2008, fig. 4.a, 1/32 degree
    Abyssal layer mean current, Basilisk, 1/24 degree
    Abyssal layer interface depth from H&H, 2008, fig. 5.d, 1/32 degree
    Abyssal layer interface depth, Basilisk, 1/24 degree
    EKE at 700 m from Chassignet & Xu, 2017, fig. 17

    EKE at 700 m from Chassignet & Xu, 2017, fig. 17

    EKE in layer 2 (750–500 m), Basilisk, 1/24 degree

    EKE in layer 2 (750–500 m), Basilisk, 1/24 degree

    EKE at 1000 m from Chassignet & Xu, 2017, fig. 18

    EKE at 1000 m from Chassignet & Xu, 2017, fig. 18

    EKE in layer 1 (1000–750 m), Basilisk, 1/24 degree

    EKE in layer 1 (1000–750 m), Basilisk, 1/24 degree

    Top layer

    Mean top layer thickness (m)

    Mean top layer thickness (m)

    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]

    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 ]

    [hurlburt2008]

    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 ]

    [hurlburt2000]

    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 ]