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Cross-shelf transport and dispersion due to baroclinic instabilities

Kristen Thyng
April 30, 2014

Cross-shelf transport and dispersion due to baroclinic instabilities

Poster presented at the European Geophysics Union (EGU) General Assembly in Vienna, Austria, in April 2014.

Kristen Thyng

April 30, 2014
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  1. Cross-shelf transport and dispersion due to baroclinic
    instabilities
    Kristen M. Thyng and Robert D. Hetland
    Oceanography, Texas A&M University, [email protected]
    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
    https://github.com/kthyng/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
    Surface-limited
    2004-2010
    Mostly without subgrid diffusion
    Used for metric calculations
    Surface salinity from 2007 and 2008 with drifters
    Salinity [color], drifters [grey]
    Submesoscale?
    Loop Current Eddies are mesoscale O(100s) km
    Shelf instabilities are O(20 − 50) km
    Sub-observational
    Ri ∼ 2 − 10
    Conclusions and Questions
    - More river input (2008), with similar winds, can lead to more
    effects from baroclinic instabilities
    - Eddies present in summer
    - Baroclinic instabilities enhance lateral dispersion and
    cross-shelf transport
    - Subgrid diffusion enhances both D and FSLE but
    changes shape of FSLE — is this correct submesoscale
    behavior in the region?
    - Want to back out velocity field characteristics with
    E(k) ∼ k−β using data
    References


    os, K., Kjellsson, J., and J¨
    onsson, B. (2013). Tracmassa la-
    grangian trajectory model. In Preventive Methods for Coastal
    Protection, pages 225–249. Springer.
    LaCasce, J. and Ohlmann, C. (2003). Relative dispersion at
    the surface of the gulf of mexico. Journal of marine research,
    61(3):285–312.
    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,
    117(C11):C11009.
    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 Operational Oceanography, 5(1):19–34.
    Surface transport more cross-shelf in 2008
    Enhanced dispersion due to eddies
    Data from LaCasce and Ohlmann (2003).
    Seasonal patterns for cross-shelf transport
    European Geosciences Union General Assembly 2014, April 27 – May 2, Vienna, Austria

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