Portland State University: Christopher Mooers
University of California, Los Angeles: Yi Chao
August 2009 – January 2011
We propose to use the Regional Ocean Modeling System (ROMS) for this proposed Gulf of Mexico (GoM) data assimilation and forecasting system. ROMS is a new community ocean circulation model that is in widespread use for estuarine, shelf, and coastal applications. Its computational kernel includes high-order advection and time-stepping schemes, weighted temporal averaging of the barotropic mode to reduce aliasing into the slow baroclinic motions, and conservative parabolic splines for vertical discretization. A redefinition of the pressure-gradient term is also applied in ROMS to reduce the pressure-gradient truncation error, which has previously limited the accuracy of terrain-following coordinate models.
The GoM model configuration will use the South Atlantic Bight and Gulf of Mexico Circulation Nowcast/Forecast (SABGOM N/F) Modeling System developed, operated and maintained by Dr. Ruoying He’s group at North Carolina State University. The spatial resolution of this operational SABGOM N/F system is 5 km. Vertically, it has 36 layers weighted to better resolve surface and bottom boundary layers. Currently, the N/F system is using the open boundary condition from the operational 1/12 degree global data assimilative HYCOM NCODA analysis, superimposed by tidal harmonics from ADCIRC western Atlantic tidal database. Surface forcing is obtained from NOAA National Operational Model Archive and Distribution System (NOMADS). We will work closely with Dr. Yi Chao of UCLA to implement a 3-dimensional variational data (3DVAR) assimilation scheme into the GoM ROMS. The ROMS 3DVAR incorporates weak constraints based on hydrostatic and geostrophic balance. The balance constraints are applied to the increment, rather than the total field. The internal dynamic consistency makes it particularly suitable for coastal regions, where there are complex coastlines, bottom topography, upwelling, fronts and eddies.