Texas-Louisiana cross-shelf transport due to submesoscale eddies

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

Transcript

1. Texas-Louisiana
   Cross-shelf Transport due
   to Submesoscale Eddies
   Kristen M. Thyng and Robert D. Hetland
   Oceanography, Texas A&M University,
   kthyng@tamu.edu
   Goal
   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¨
   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
   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
   Submesoscale?
   Loop Current Eddies are mesoscale O(100s) km
   Shelf instabilities are O(20 50) km
   Sub-observational
   Ri ⇠ 2 10
   References
   D¨
   o¨
   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–
   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 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
   Dispersion
   Baroclinic instabilities, present in the summer, enhance
   dispersion. Data from LaCasce and Ohlmann (2003).
   Conclusions
   - 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
   Text
   

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