Gulf of Mexico Nature Run

Gulf of Mexico Nature Run
The Gulf of Mexico (GoM) has been chosen by OMOC for performing future ocean OSSEs that are able to span a wide variety of ocean processes. The GoM combines coastal and shelf areas with a very energetic western boundary current, typical of the open ocean, namely the Gulf Stream (GS). Within the Gulf, the GS branch is called Loop Current (LC), feeding to the Florida Current (FC) through the Florida Straits. The LC/FC system is prone to instabilities and is accompanied by a rich eddy field. The coastal and shelf areas are characterized by intense coastal-to-offshore processes. Examples are: the transport of low salinity waters controlled by the Mississippi River plume and wind influence on the shelf, with further interaction with the LC and its associated eddy field; shelf break processes controlled by LC intrusions on the West Florida Shelf or FC intrusions along the Florida Keys archipelago. This project focuses on high-resolution simulations of the GoM to be used as a Nature Run in future prototype ocean OSSEs, mimicking ocean processes of interest that the observing system under study will sample.
The OMOC regional GoM-HYCOM model has a horizontal resolution of 1/50° (~2 km) and 32 vertical levels, which are optimized for resolving the Mississippi River plume dynamics (Schiller et al., 2012; Kourafalou and Androulidakis, 2013; Androulidakis and Kourafalou, 2013), as well as the deep GoM dynamics. The river forcing uses daily discharges for 15 major rivers, while other rivers are represented by monthly climatological values. The simulation uses a high-resolution bathymetry compiled at FSU-COAPS, based on 3 datasets of bottom topography and coastlines. The atmospheric forcing is adapted from the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) model run by the U.S. Navy (27 km, 3 hourly outputs). The OMOC 1/50° GoM-HYCOM is nested into the operational Global HYCOMsimulation, using daily outputs. This project extends the work performed with the free-running GoM-HYCOM model at 1/25° resolution, which was evaluated with observations as another regional Nature Run candidate for ocean OSSEs by Le Hénaff et al. (2012).

Maps of GoM-HYCOM Sea Surface Salinity (SSS, right panels) for July 31st, 2011 (top) and September 15th, 2011 (bottom), exhibiting the signature of Mississippi river-borne fresher waters, as they are advected eastward and offshore. MODIS Ocean Color maps for the same dates (left panels) illustrate similar patterns of riverine waters, observed through their associated biological productivity, due to their high nutrient content. The good qualitative agreement highlights how the 1/50° GoM-HYCOM, developed as an OMOC regional Nature Run, is able to represent coastal and shelf dynamics, as well as the realistic variability of the Mississippi River (MR) plume, under variable river discharge and wind conditions, with further modifications by offshore circulation. On July 31st, the plume was directed eastward (under westerly winds) and partially toward the GoM interior (under the influence from offshore mesoscale eddies). On September 15th, the wind turned to a westward direction, limiting the eastward plume extension; Mississippi waters remained close to the Delta, in both model and observations. (Note: For a bigger view please click on the figure.


Androulidakis, Y.S. and V.H. Kourafalou, 2013. On the processes that influence the transport and fate of Mississippi waters under flooding outflow conditions. Ocean Dynamics, doi:10.1007/s10236-012-0587-8.
Kourafalou, V.H. and Y.S. Androulidakis, 2013. Influence of Mississippi induced circulation on the Deepwater Horizon Oil Spill transport. J. Geophys. Res., 118, 1–20, doi:10.1002/jgrc.20272.
Le Hénaff, M., V.H. Kourafalou, Y. Morel and A. Srinivasan, 2012. Simulating the dynamics and intensification of cyclonic Loop Current frontal eddies in the Gulf of Mexico. J. Geophys. Res., 117, C02034, doi:10.1029/2011JC007279.
Schiller, R.V., V.H. Kourafalou, P.J. Hogan and N.D. Walker, 2011. The dynamics of the Mississippi River plume: impact of topography, wind and offshore forcing on the fate of plume waters. J. Geophys. Res., doi:10.1029/2010JC006883, 116, C06029.