Title page for ETD etd-01092015-211259

Type of Document Dissertation
Author Allahdadi, Mohammadnabi
Author's Email Address mallah1@lsu.edu
URN etd-01092015-211259
Title Numerical Experiments of Hurricane Impact on Vertical Mixing and De-Stratification of the Louisiana Shelf Waters
Degree Doctor of Philosophy (Ph.D.)
Department Oceanography
Advisory Committee
Advisor Name Title
Li, Chunyan Committee Chair
Keim, Barry D Committee Member
Rabalais, Nancy Committee Member
Walker, Nan D. Committee Member
Ikuma, Laura Dean's Representative
  • Hypoxia
  • Sea Surface Temperature
  • Hurricane-induced Hydrodynamics
  • Richardson Number
  • Upwelling and Downwelling
Date of Defense 2014-11-12
Availability unrestricted
The numerical model FVCOM (Finite Volume Community Ocean Model) was applied to study the effects of Hurricane Katrina on the vertical mixing over the Louisiana shelf and the process of post-storm re-stratification. Wind field from Hurricane Katrina was generated using a single vortex analytical model and was evaluated using available wind measurements over the shelf. Simulations of shelf circulation under Hurricane Katrina were done through several numerical tests to find the best approach for treating vertical eddy viscosity. Model results for the shelf during Katrina demonstrated opposite currents between surface and bottom for most of the shelf area. Results also show current intensification between the eye and the Birds-foot delta, where current speed reached ~ 3.5 m/s at one time.

Shelf-wide mixing and re-stratification during and after Katrina were studied by examining the salt and heat transports. Climatological salinity and temperature profiles for August from NOAA were used as the initial conditions. Model performance in simulating water temperature was evaluated using the cloud transparent microwave band SST data (OI-MW) along the shelf break. Model was also evaluated for the mixed layer depth (MLD) calculated from model results which were compared with that from the OI-MW SST data and a theoretical model.

During Katrina, the SST decreased up to 1C for areas outside of the 1-1.5 Radius of maximum wind (RMW), while inside the RMW and west of the Birds-foot delta 2-3.5 C. Consequently, the mixed layer depth (MLD) left of the 1-1.5 RMW region was smaller than 10 meter. Inside this region the MLD was up to 40 meters. By inspecting the mixing and re-stratification pattern using the model outputs, conceptual models for water column mixing during the hurricane and re-stratification were proposed. It was concluded that the complete recovery of the water column temperature was not achieved even after 14 days following the landfall and it is likely that the effect of solar radiation may qualitatively change the conclusion. Hence, the effect of solar insolation on the shelf heating was simulated separately for non-hurricane summertime conditions. This simulation demonstrated the significant effect of solar insolation on the shelf heating and stratification of the water column.

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