On the development of a Regional Hydrodynamic Model around Florida Bay and the Florida Keys
Villy H. Kourafalou and Thomas N. Lee
University of Miami, RSMAS, Miami, Fl
A comprehensive, three-dimensional hydrodynamic model of the coastal seas adjacent to Florida Bay and the Florida Keys is under development (Figure 1). The study goal is to link the shallow coastal regions that encompass Florida Bay and the Florida Keys to adjacent oceanic and shelf flows that play an important role in the water circulation and exchange. The modeling strategy is to follow a nested and downscaling approach, where the regional model provides the link between coastal models of Florida Bay and the Florida Keys with a larger scale Atlantic Ocean and Gulf of Mexico hydrodynamic model. The regional model has an intermediate resolution (lying between the coarse resolution of the large scale model and the fine resolution of the coastal scale models) and it provides appropriate boundary conditions for the limited area models of the Florida Bay and Florida Keys regions. This approach ensures that the coastal models receive inputs from adjacent and remote sources, so that the calculated flows in the coastal areas of interest are realistic. Furthermore, the regional model provides downscaled fields of wind and heat and salt fluxes, that are the product of larger scale atmospheric models. These fields introduce the regional South Florida meteorological effects on the limited area coastal models.
The main objective of the study is to numerically simulate the key mechanisms that control the interaction between Florida Bay, the Florida Keys, the coastal waters of the adjacent shelf, and large-scale off-shore oceanic flows. The related processes have been identified through analysis of data from ongoing observational programs. Numerical simulations are being planned to test the data based hypotheses and determine which processes must be incorporated to successfully predict the transport rates and pathways of waters that exit Florida Bay toward environmentally sensitive areas such as the Florida Keys reef tract and the Dry Tortugas Ecological Reserve. An example is a process oriented numerical study on the net southward flow that couples the eastern Gulf and Atlantic coastal region of the Keys. This flow transports low-salinity discharges from rivers in the eastern Gulf and western Everglades around Cape Sable to western Florida Bay where they can interact with interior waters of the Bay as well as the Atlantic coastal waters of the Keys.
The regional hydrodynamic model is an implementation of the HYCOM (Hybrid Coordinate Ocean Model, http://panoramix.rsmas.miami.edu/hycom/), a finite-difference hybrid isopycnal/sigma/z-level model. This model has been developed on a hybrid vertical coordinate system, in order to overcome problems faced by traditional vertical coordinate choices (z-level, terrain-following sigma, isopycnic), that are not optimal everywhere in the ocean. HYCOM behaves like a conventional sigma model in very shallow and/or unstratified oceanic regions, like a z-level coordinate model in the mixed layer or other unstratified regions, and like an isopycnic-coordinate model in stratified regions. In doing so, the model combines the advantages of the different types of coordinates in optimally simulating coastal and open-ocean circulation features. Furthermore, depending on the application, HYCOM can be run in isopycnic, sigma or hybrid mode. This flexibility makes HYCOM an excellent choice for the current regional model development, as it can be easily coupled with a range of coastal Florida Bay and Florida Keys coastal models.
The South Florida regional HYCOM model is under development. It includes the southern part of the western Florida shelf and the Florida Straits on a 2-3 km resolution and it is being coupled with an existing large scale HYCOM model with 6-7 km resolution. The regional model encompasses the inner Florida Bay model domain (Figure 1) and it is thus suitable to provide boundary conditions for high resolution Florida Bay and Florida Keys coastal models. The regional South Florida model can perform suitable long term and event oriented simulations to compute and deliver all the necessary hydrodynamic parameters at the boundaries of the coastal models. This nested numerical approach ensures that simulations within Florida Bay and the Florida Keys are realistic, as they are sustained by interactive links to the adjacent large scale flows.
Preliminary results support the need for a nested modeling approach. The Loop Current and the Florida Current provide a mechanism for the connectivity of coastal waters around South Florida. This is a finding that is supported by the observations. Model results suggest that the summer period favors advection of low salinity waters from remote areas like the west Florida shelf and the Mississippi River toward Florida Bay and the Florida Keys. Supportive data from the summer of 1998 are presented.
Villy Kourafalou, University of Miami, RSMAS/MPO, 4600 Rickenbacker Causeway, Miami, Fl, 33149, Phone: 305-361-4905, Fax: 305-361-4696, email@example.com, Question 1
Figure 1: The seas adjacent to Florida Bay: Gulf of Mexico, West Florida shelf and Florida Straits; the thick rectangular frame marks the regional South Florida model area; the thick dashed line marks the inner Florida Bay model area.