Evaluation of the Northern Gulf of Mexico Littoral Initiative Model Based on the Observed Temperature and Salinity in the Mississippi Bight

Abstract

Temperature and salinity measurements from the Northern Gulf of Mexico Littoral Initiative (NGLI) survey during August 30 - September 14, 2000 reveal a high level of temporal and spatial variability in the Mississippi Bight. To support scientific studies using a numerical model, a three-dimensional hydrodynamic Estuarine and Coastal Ocean Model (ECOM) is implemented in the Mississippi Bight. The ECOM is run with realistic topography, stratification and meteorological forcing to hindcast circulation on a shallow and highly variable shelf of the Mississippi Bight. The results of the model are compared with observation to evaluate the ECOM performance on different temporal scales. Based on the area oceanography and data availability, three temporal scales are chosen for model/data comparison: fine scale (less than an hour), diurnal, and large scale (a two-week period). Limitations of the ECOM application on each scale are discussed. The model is capable to reproduce observed water masses, describe spatial distribution of water properties, and simulate areas with high horizontal gradient such as freshwater plumes. However, delayed response to meteorological forcing, overestimated mixing rates and uncertainties in computation of river discharges result in statistically significant bias in the simulations. Along with traditional linear correlations from all observational points and spectral analysis over the diurnal cycle, a new technique of model validation is introduced. The technique is a new application of an existing variational interpolation method. Detailed description of the method and numerical procedure allow one to apply this technique to any oceanographic data with prescribed data variances for model/data comparison.