NOAA/Nation Ocean Service Columbia River Estuary Operational Forecast System
The new National Ocean Service (NOS) operational forecast system is based on a three-dimensional hydrodynamic model, the Semi-implicit Eulerian-Lagrangian Finite Element (SELFE) model developed at OHSU. SELFE is an open-source, community-supported, finite-element model for river-to-ocean modeling, with an unstructured grid in the horizontal dimension, hybrid SZ coordinates in the vertical dimension (with Z layers being optional), and flexibility in representing the bathymetry and vertical structure of the water column.
The CREOFS grid consists of 74,061 nodes and 142,684 elements and includes the upper and lower Columbia River and estuary. Grid resolution ranges from 39 km on the open ocean boundary to approximately 100 m near the coast, indicating the flexibility of the grid size based on bathymetry from the deep ocean to the coast. In addition, finer elements (approximately 100 m to 10 m) are specified along in-bay navigational channels to better represent the currents.
The testing and setup of the CREOFS nowcast/forecast system was implemented by NOAA's Coast Survey Development Laboratory (CSDL), in coordination with NOAA's Center for Operational Oceanographic Products and Services (CO-OPS) and OHSU. Simulations were made to validate the performance of the model in both tidal and synoptic hindcast scenarios. The model's performance in these scenarios was then assessed through skill assessment criteria and software developed by CSDL.
A tidal simulation was conducted for the one-year period from April 2007 to April 2008. For operational model development, this tidal simulation is normally made using constant salinity/temperature and only a tidal forcing along the open ocean boundary. With the Columbia River, however, the tidal response at stations upstream of the main estuary is highly dependent on the interaction with the river discharge. Therefore, the tidal simulation for CREOFS was made using both an open ocean tidal forcing and observed time series of river discharge imposed along the Columbia, Willamette, Cowlitz, Clackamas, Lewis, and Fraser Rivers.
A synoptic hindcast simulation was set up for the two-year period of April 2007 to April 2008. In addition to the tidal forcing and river discharges, the model was also forced with atmospheric inputs from the North American Regional Reanalysis product. Also, salinity and temperature were initialized using the U.S. Navy Coastal Ocean Model (NCOM) and were slightly nudged to NCOM values in the open ocean during the simulation. Nontidal water levels from NCOM were also added on as a time series to the tidal forcing along the open ocean boundary. In the operational implementation of CREOFS at NCEP, NCOM will be replaced with the Global Real-Time Ocean Forecast System forecasts of salinity, temperature and nontidal water levels as a boundary condition. Both the tidal and synoptic hindcast simulations were evaluated using NOS' skill assessment software developed by CSDL. Outputs from the model simulations were saved at a 6-minute interval from station locations where observations were available, including stations maintained by CO-OPS, US Geological Survey, US Army Corps of Engineers, and OHSU. Variables evaluated included the total water levels, tidal water levels, currents, salinity and temperature.
Operational implementation of CREOFS is made on NOAA's Central Computer System (CCS) and has been developed to provide the maritime community with nowcasts (i.e. analysis) and short-term (2 day) forecast guidance of water levels, currents, water temperature, and salinity. Time series graphics at station locations (locations of CO-OPS observation stations or navigationally strategic locations, for example) and aerial animations of three subdomains for five parameters (wind, water levels, surface currents, surface water temperature and surface salinity) are displayed on a CO-OPS web site.