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Texas-Louisiana cross-shelf transport due to submesoscale eddies

Kristen Thyng
February 27, 2014

Texas-Louisiana cross-shelf transport due to submesoscale eddies

Poster presented at the AGU Ocean Sciences meeting in Honolulu, HI, in February 2014.

Kristen Thyng

February 27, 2014

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  1. Texas-Louisiana
    Cross-shelf Transport due
    to Submesoscale Eddies
    Kristen M. Thyng and Robert D. Hetland
    Oceanography, Texas A&M University,
    [email protected]
    Study enhanced dispersion and cross-shelf transport due to baroclinic instabilities along river
    plume edge
    TX-LA shelf numerical grid
    Numerical Model
    Regional Ocean Modeling System (ROMS) circulation model of the
    Texas-Louisiana shelf
    Includes wind and rivers, nested in HYCOM Gulf model
    Validation: (Zhang et al., 2012a,b)
    Particle Tracker
    TRACMASS, runs trajectories natively on staggered Arakawa C
    grid (D¨

    os et al., 2013)
    ...wrapped in Python: TracPy
    Drifter Simulations: From River Inputs
    Drifters started every model output (4 hours), May-August
    Run for 90 days
    2007 and 2008
    Started where Mississippi and Atchafalaya rivers are input
    Each associated with part of the river volume transport inflow
    Drifter Simulations: Uniformly Distributed
    Started daily sets of drifters seeded 1 km apart in x and y which
    ran for 30 days
    Included diffusion to the particle trajectories with AH = 5 m2s 1
    Used for mean separation distance calculation
    Surface salinity from 2007 and 2008 with drifters
    Salinity [color], drifters [grey]
    Wind was similar in 2007 and 2008 but more river
    discharge in 2008
    ) ... expect more instabilities on shelf in 2008
    Loop Current Eddies are mesoscale O(100s) km
    Shelf instabilities are O(20 50) km
    Ri ⇠ 2 10

    os, K., Kjellsson, J., and J¨
    onsson, B. (2013). Tracmass - A La-
    grangian trajectory model. In Preventive Methods for Coastal Pro-
    tection, pages 225–249. Springer.
    LaCasce, J. and Ohlmann, C. (2003). Relative dispersion at the sur-
    face of the Gulf of Mexico. Journal of Marine Research, 61(3):285–
    Zhang, X., Hetland, R. D., Marta-Almeida, M., and DiMarco,
    S. F. (2012a). A numerical investigation of the Mississippi and
    Atchafalaya freshwater transport, filling and flushing times on
    the Texas-Louisiana Shelf. Journal of Geophysical Research,
    Zhang, X., Marta-Almeida, M., and Hetland, R. D. (2012b). A
    high-resolution pre-operational forecast model of circulation on the
    Texas-Louisiana continental shelf and slope. Journal of Opera-
    tional Oceanography, 5(1):19–34.
    This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative
    2014 Ocean Sciences Meeting, February 23–28, 2014, Honolulu, Hawaii

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  2. Surface transport for drifters started in each month
    Transport associated with drifters started in each month and run for 90 days shows largest cross-shelf transport in May
    and run through the summer
    Baroclinic instabilities, present in the summer, enhance
    dispersion. Data from LaCasce and Ohlmann (2003).
    - More river input (2008), with similar winds, can lead to
    more effects from baroclinic instabilities
    - River water input in May leads to eddies in June-July
    - Baroclinic instabilities enhance lateral dispersion
    - Baroclinic instabilities enhance cross-shelf transport
    River connectivity over time
    River water input throughout May shows spreading over shelf throughout July
    2014 Ocean Sciences Meeting, February 23–28, 2014, Honolulu, Hawaii

    View Slide