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¨
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