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.

Transcript

1. Cross-shelf transport and dispersion due to baroclinic
   instabilities
   Kristen M. Thyng and Robert D. Hetland
   Oceanography, Texas A&M University, kthyng@tamu.edu
   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¨
   o¨
   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
   D¨
   o¨
   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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