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
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