Over the last five years, part of the CESR group developed a unique simulation and modeling code. This code accounts for the many scales that must be considered when studying broad ocean phenomena, as well as coastal circulation systems. Called the Regional Oceanic Modeling System (ROMS), the code is used at UCLA and at several other places. Most of the various numerical pieces (computation kernel, realistic vertical mixing parametrization model, robust boundary conditions adapted to long-term integrations, variable biogeochemistry model, sediment model and Lagrangian capability) were fit together in ROMS. We are now in a position to be able to study any regional coastal system and how it and global systems influence each other. We are running ROMS simulations on NCSA's supercomputers, using several hundred thousand hours of computation time each year. [UCLA ROMS group photo includes, back row: Xavier Capet, Alexander Shchepetkin, Hartmut Frenzel, Keith Stolzenbach, and Olaf Haupt; front row: Patrick Marchesiello, James McWilliams, and Nicolas Gruber.]

Our initial goal has been to create an accurate model of the North American West Coast (NAWC) regional system and to perform realistic long-term integrations of the California Current System (CCS). Solutions in statistical quasi-equilibrium have been obtained and analyzed to unravel the intricate dynamics of the CCS.  Similarly, a description of the CCS ecosystem quasi-equilibrium is underway.

To cope simultaneously with phenomena that involve time and length scales with different orders of magnitude (rapid air temperature and wind changes versus carbon dioxide levels or slow salinity variations in the water; local circulation patterns influenced by localized winds, storms, and coastline irregularities versus large scale circulation strongly tied to broad atmospheric weather systems), we have chosen an approach based on the nesting of grids with increasingly high resolution. These nested grids work much like Adaptive Mesh Refinement techniques. A simulation starts with the coarsest resolution grid (the parent grid) that measures a mesoscale phenomena. Finer resolution "child" grids are then advanced by one step with boundary conditions provided an uptodate parent solution. This goes on as long as child grids exist. The parent grid is then modified using the information obtained from the child grids, to create a more accurate model that measures both large- and small-scale events over time. So far, we have run simulations that use as many as three grid levels off the Central California Coast and four grid levels off Southern California (with a finest grid measuring at 500-meter intervals in the Santa Monica Bay).  The high resolution solutions obtained on the highest grid levels allow us to develop coastal engeneering and water quality applications.

In the same spirit of looking at interactions between different time and length scale dynamics, we began generating simulations of the circulation (and soon ecosystems and geochemistry) for the entire Pacific basin and then scaling down those simulations to examine conditions specific to the NAWC. This work is aimed at a better understanding of large-scale low frequency climate fluctuations  (e.g., the periodic warming of the sea surface temperature in the tropical Pacific El Niño Southern Oscillation, also the lower frequency signals of the Pacific Decadal Oscillation)  affect regional currents and ecosystems.