Research ArticleOCEANOGRAPHY

Submesoscale Rossby waves on the Antarctic circumpolar current

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Science Advances  28 Mar 2018:
Vol. 4, no. 3, eaao2824
DOI: 10.1126/sciadv.aao2824
  • Fig. 1 SeaSoar section and MVP survey.

    (A) Map of survey site with temperature (color, main panel) and Absolute Dynamic Topography (ADT), and locations of the Seasoar section and MVP survey with surface temperature (colored dots) and surface velocity vectors. (B) Seasoar section from 9 May with depth-averaged along-front current speed (top) and temperature and potential density (bottom, color shading and white contours). The corresponding model initial conditions (ICs) are also shown. The potential density contour interval is 0.01 kg m−1. (C) MVP survey conducted on 15 May at the location indicated in (A). The time of each section is converted to advected distance by multiplying the approximate speed of the ACC jet (1.2 m/s). The top surface shows temperature from the MVP, averaged above a depth of 20 m (shading), and from the ship’s flow-through intake (colored dots). The 3°C isotherm is interpolated into along-track, advected distance, and depth coordinates and displayed as a gray isosurface.

  • Fig. 2 Linear stability analysis of the model initial conditions shown in Fig. 1B.

    (A) Perturbation energy source terms for a basic state with (solid) and without (dotted) the ACC jet. Blue dots indicate the most unstable mode. (B) Density perturbations associated with the most unstable mode with (solid blue) and without (dotted blue) the ACC jet. Surface density contours (red) and the ACC jet profile (black) are also shown.

  • Fig. 3 Nonlinear numerical simulations.

    (A) Equivalent temperature contour length, Leq, as defined in Eq. 3, normalized by its minimum value, L0, and averaged from 3° to 4.5°C (solid lines). Shaded regions indicate ±1 SD about the average over the temperature range. Dashed lines indicate the mean value of Leq from each model, subsampled (with a resolution of 4 km × 400 m) to approximate the spacing of the MVP measurements. Insets show the temperature at a depth of 50 m. (B) Space-time diagram of the streamwise velocity at a depth of 50 m and a cross-stream distance of 4.25 km for the late stages of the model simulation with a jet included. Note that the velocity associated with the ACC jet at this location has been subtracted from u. White dashed lines have a slope equal to the phase speed calculated from Eq. 4 with the indicated along-stream wavelengths and independent of the cross-stream direction. (C) Power spectrum associated with the along-stream velocity at the same cross-stream distance as in (B), calculated for the full duration of the model with an ACC jet. Solid white and black lines indicate the dispersion relation from Eq. 4 for mixed layer baroclinic modes (n = 1) and barotropic modes (n = 0). In both cases, the cross-stream wave number is set to zero.

  • Fig. 4 Average temperature and density sections.

    (A) Composite temperature (color) and density (black contours), averaged for all MVP sections. (B) Along-stream (x) averaged temperature (color) and density (black contours) from the model with the ACC jet at 53 days. The initial temperature was independent of depth in the model.

  • Fig. 5 Vertical velocity and subduction.

    rms vertical velocity at z = 50 m depth with respect to an average in the x direction, from the model without (A) and with (B) the ACC jet. White contour lines show x-averaged density with a contour interval of 0.01 kg m−1. Volume of water with potential density σθ > 26.95 kg/m3 subducted below z = −50 m. The slope of the dashed lines corresponds to the labeled volumetric subduction rate.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaao2824/DC1

    Observations

    Numerical simulations

    Model initial conditions

    Subduction estimate

    fig. S1. Wind stress (N/m2) and wind angle (degrees from east) calculated using the algorithm of Large and Pond (36).

    fig. S2. Profiles of the buoyancy (blue), temperature (red), and depth-averaged velocity (green) associated with the model initial conditions and the linear stability analysis.

    fig. S3. Probability density functions of potential density at the end of each simulation.

    fig. S4. Subducted volume (units of m3) for the simulations reported in the main text with two opposing fronts surrounding a dense filament and two additional simulations with just the outer front present.

    References (3741)

  • Supplementary Materials

    This PDF file includes:

    • Observations
    • Numerical simulations
    • Model initial conditions
    • Subduction estimate
    • fig. S1. Wind stress (N/m2) and wind angle (degrees from east) calculated using the algorithm of Large and Pond (36).
    • fig. S2. Profiles of the buoyancy (blue), temperature (red), and depth-averaged velocity (green) associated with the model initial conditions and the linear stability analysis.
    • fig. S3. Probability density functions of potential density at the end of each simulation.
    • fig. S4. Subducted volume (units of m3) for the simulations reported in the main text with two opposing fronts surrounding a dense filament and two additional simulations with just the outer front present.
    • References (37–41)

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