Where the Mississippi River Delta landmass protrudes out into the Gulf of Mexico, coastal currents can mix with offshore surface waters. "Oil that is initially offshore, it'll come near shore and bump up against the Mississippi River Delta. And then it gets whipped around and swept into this coastal current."
Additionally, there's an unusually deep feature on the ocean floor to the southwest of the Delta, called the Mississippi Canyon. The irregular ocean depths, or bathymetry, between the Delta and the Canyon; prevailing winds; and fresh water that drains from the Delta all contribute to water mass exchange.
To show oil would be concentrated where currents converge, and dispersed where currents diverge, "We had specific buoyancy restoring term in the model that would bring oil back to the surface." He was able to account for the tendency of oil, pulled under by currents, to rise back to the surface-critical to forecasting material transport. A three-dimensional framework made these zones of divergence and convergence easier to identify than in 2010 (Eulerian versus Lagrangian). (A future model that sought to include subsurface oil in the initial inputs would need a more complex accounting of how hydrocarbons interact with seawater and chemical dispersants.)
Jolliff doesn't compare his predictions to what federal agencies made at the time, because they were continuously updating their simulations. "The take home message is that COAMPS was able to forecast the atmospheric and oceanographic conditions that made that funnel [of water mass exchange] operate. And so what was happening in the model then happened in reality."
Mesoscale: why the oil spill didn't hurt Florida beaches
Next, Jolliff sought to explain what
|Contact: Kyra Wiens|
Naval Research Laboratory