Abstract
A multi-decadal simulation of ocean circulation in the northern Gulf of Mexico produces strong submesoscale instabilities in the Mississippi/Atchafalaya plume fronts. The model skill in reproducing these submesoscale frontal eddies over the Texas-Louisiana shelf is assessed using simulated and observed salinity and velocity fields as a way to investigate simulation accuracy and quantify the variability of frontal eddies. The model successfully reproduces mean salinity structure observed in multi-year densely sampled CTD profiles. Variability associated with submesoscale eddies is the largest source of error in predicted salinity. On the other hand, the model is statistically able to reproduce the magnitude and characteristics of frontal eddies; metrics for eddy kinetic energy are similar between the observations and simulation, and observed horizontal salinity gradients have similar occurrence rates in the model when sampled in a manner similar to the observations. Seasonal and inter-annual variability of frontal eddies is associated with the volume of freshwater onto the shelf and wind stress. Wind stress, the highest in winter and lowest in summer, contributes to the suppression of baroclinic instability during non-summer seasons. River streamflow, highest in spring, creates strong horizontal and vertical density gradients. These strong horizontal density gradients, along with weak seasonal upwelling-favorable winds that tend to broaden the plume, are the primary factors in exciting submesoscale instabilities during summer on the Texas-Louisiana shelf. At decadal scales, streamflow, EKE, and salinity gradients have a positive correlation suggesting that long-term variability of frontal eddies may be influenced remotely by inter-annual variability in the Mississippi River outflow.
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Acknowledgements
The model was implemented on High Performance Computing Clusters, Ada maintained by Texas A&M University. The computational resources and in-kind supports were kindly provided by Texas A&M High Performance Research Computing. We acknowledge the following organizations, National Oceanic and Atmospheric Administration (NOAA), European Center for Medium-Range Weather Forecast (ECMWF), Copernicus Marine Service, U.S. Naval Research Laboratory (NRL), Geochemical Environmental Research Group, U.S. Army Corps of Engineers (USACE), and U.S. Geological Survey (USGS) for providing input data to run hindcast models and observing data to validate our model. The hindcast model output used in this study is accessible at http://barataria.tamu.edu:8080/thredds/catalog.html?dataset=txla_hindcast_agg.
Funding
This project was funded by Texas General Land Office (Grant number 10-096-000-3927).
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Kobashi, D., Hetland, R. Reproducibility and variability of submesoscale frontal eddies on a broad, low-energy shelf of freshwater influence. Ocean Dynamics 70, 1377–1395 (2020). https://doi.org/10.1007/s10236-020-01401-4
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DOI: https://doi.org/10.1007/s10236-020-01401-4