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