Validation of the NOS Galveston Bay Nowcast/Forecast SystemHydrodynamic Models: Review and New Perspectives

摘要

The National Ocean Service (NOS) has developed an operationalnowcast/forecast system for Galveston Bay using a modified version of the Blumberg-Mellor (1987) three-dimensional hydrodynamic model extended to orthogonalcoordinates by Blumberg and Herring (1987) as discussed by Schmalz (1996, 2001). Thenowcast component works directly from the National Water Level Operational Networkdatabase using standardized readers. During the forecast component the NationalWeather Service's North American Mesoscale, River, and Extratropical Storm Surgemodels are used to provide the meteorological, surface water inflow, and Gulf of Mexicosubtidal water level forcings, respectively. In addition, a one-way coupled higherresolution Houston Ship Channel model (Schmalz, 2000) has also been incorporated intothe system. Hourly nowcasts of the previous 24 hour period and four times daily 30 hourforecasts of water surface elevation and currents, as well as three-dimensionaltemperature and salinity are performed using both bay and channel models.Initially, hindcast studies over June 1995, January 1995, October 1994, and April1996 were performed to validate the models for tidal and subtidal effects. Next, prior tooperational implementation, the experimental nowcast and forecast results were assessedover the one-year period April 2000 through March 2001 based on the NOS (1999)formal acceptance statistical criteria.The methods to estimate numerical uncertainty in computational fluid dynamiccomputations proposed by Roache (1997, 1998) are investigated as to theirappropriateness for these three-dimensional, unsteady, stratified, estuarine flow models.We first examine the basic procedures. Next we suggest how they might be applied to thebay and channel hydrodynamic model calculations. We consider both the hindcast andnowcast/forecast calculations. Potential difficulties and challenges are outlined for bothcalculation types. Finally, next steps are advanced to seek to improve the validationprocedure.