The calibration/validation of a Mississippi Sound/Bight model

Abstract

A regional scale forecast modeling system of the Mississippi Sound/Bight and adjoining estuaries and bays has been developed as part of the Northern Gulf of Mexico Littoral Initiative (NGLI), a multi-agency program spearheaded by NAVOCEANO and USEPA Office of Gulf of Mexico Program. The system, based on the model called ECOMSED, provides a reliable means of predicting the littoral circulation and the salinity and temperature structure of the region. The modeling framework adopts a high-resolution orthogonal curvilinear grid which resolves the relevant bathymetric and coastline features, especially in the vicinity of the barrier islands and ship channels. In order to ensure that the model is capable of predicting the oceanography of the Mississippi Sound/Bight, a thorough calibration and validation effort has been conducted against field observations during September 2000. Point-to-point and spatial comparisons of sea surface elevation, temperature, salinity and water currents have been conducted. The calibration and validation efforts have been supplemented by rigorous analyses to understand the sensitivity of the model predictions to various forcing functions. The estuarine processes controlled by winds and freshwater discharges have been identified and quantified for Mobile Bay, Biloxi Back Bay, Bay St. Louis and Mississippi Sound/Bight through a series of model sensitivity simulations. Estimates of the variances in model predictions have been made using a First Order Variance Analysis (FOVA) method. Percent contribution of bathymetry, temperature and salinity boundary conditions, meteorological conditions and freshwater inflows to variances in model prediction has been determined. The bathymetry and freshwater flows are found to contribute most in the variances in temperature, salinity and transport in the Mississippi sound area. Where as wind plays a major role in the variances in model prediction in the Mississippi Bight (mid shelf) region. The ECOM model, calibrated and validated in this study, is currently in operational mode in the Major Shared Resource Center (MRSC) of NAVOCEANO at Stennis Space Center, Mississippi and the model results are available in the NGLI website at www.navo.navy.mil/NGLI.