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ACCESS NUMBER: 30660-19936
variability. It was also able to reproduce observed stratification moderately well
(Wiseman et al., 2000).
OBJECTIVES: This study presents some new physical oceanographic modeling
results obtained for the Texas-Louisiana shelf, as well as a review and assessment of
past modeling efforts for this region. Extensive data sets are available from the
Louisiana-Texas inner shelf region, and provide a vast source of information for model
development, model forcing, and model verification.
DESCRIPTIONS: Several simple local models were successfully run for hindcasting
observations, and results are presented in this study. Existing reduced dimensionality
models, local wind-driven models, and a fully three-dimensional, time-dependant model
of the region were employed in hindcast mode. Model output obtained for this study was
compared with observational data, and information from independent data was used in
model development and forcing. The value of including such factors as bottom
dissipation, far field forcing, and alongshore pressure gradients in modeling the
Louisiana Coastal Current was examined. These models have had some limited
success in hindcasting observations, but all have issues that remain and these are
discussed.
SIGNIFICANT CONCLUSIONS: In an attempt to discern the plausibility of treating the
Louisiana Coastal Current as an arrested topographic wave (Csanady, 1978), we
applied an existing vertically-integrated, non-linear numerical model forced by monthly
mean wind fields. The results were intriguing but inconclusive. While the momentum
balance generally appeared to be in quasi-steady state, i.e. the local accelerations were
negligible compared to other forces, the advective accelerations in the model were, at
specific sites, non-negligible. More interesting was the fact that the dominant balance of
forces in the model was between the Coriolis forces, the surface wind stress, and the
pressure gradients.
A qualitatively acceptable comparison of output from the Yankovsky and Chapman
model with observations suggests that further development of a robust, time-dependent
theory would be beneficial.
Comparisons of full water column velocity measurements from a bottom-mounted
ADCP and alongshore bottom pressure gradients are far less satisfying. The bottom
layer alongshore currents are significantly coherent with the observed alongshore
pressure gradients in bands between 25 to 33 hours and near 50 and 100 hours. The
source of the pressure gradient is unclear.
STUDY RESULTS: A summary and critique of model results is presented, as well as
suggestions for fruitful areas of future progress and appropriate uses for these various
types of models on the Louisiana-Texas inner shelf region.
There appear to exist situations in time and space along the Louisiana-Texas inner shelf
where the bathymetry is sufficiently simple and a single forcing function sufficiently
