A Prototype Storm Response Monitoring and Forecast System for the Western Gulf of Maine
This proposed research addresses the issue of the importance of ocean waves and hydrodynamic nonlinearities for the accurate prediction of the response of the western Gulf of Maine to storm forcing. Here, "response" means the added rise in sea level (above normal tides) due to the combined effects of storm-related waves, high winds and decreased atmospheric pressure.
We hypothesize that both the nonlinear interaction between storm-wind-induced surface gravity wave currents and the relatively large tidal and wind-induced currents in the coastal ocean significantly alter the response of coastal Gulf of Maine sea level to storm forcing.
To test this hypothesis, we propose to add a surface wave model to the three-dimensional, nonlinear Dartmouth numerical circulation model and to evaluate the accuracy of the combined model hindcasts (past scenarios) in terms of archived data sets. The resulting model system will be the core element of a prototype ocean sea level monitoring and forecast system that will be forced by an appropriate suite of real-time operational government meteorological, sea level, surface wave and river discharge data and their products.
We will adapt an existing regional data and information management system to:
1) Link the operational forcing data and the ocean model system
2) Serve useful products to regional emergency management officers
The specific objectives of the proposed Sea Grant research are to:
1) Couple a combined surface gravity wave/current bottom friction model to the Dartmouth nonlinear circulation model, called QUODDY
2) Implement a suitable scheme for specifying a space/time variable sea level pressure along the open ocean boundary of QUODDY
3) Implement a scheme for the near-realtime forcing of QUODDY with realistic atmospheric pressure and wind stress
4) Conduct hindcast studies of the storm response of the western Gulf, with a focus on the winter 1987, spring 1994 and winter 1995-96 periods of existing measurements
5) Assess the quality of the model system storm response through comparison with existing observations
6) Develop storm response model products suitable for emergency management office use
Our approach is to adapt the Dartmouth three-dimensional (3-D), finite-element, nonlinear hydrodynamic model of the extended Gulf of Maine circulation (called QUODDY; Lynch and Werner 1991) to the proposed task. The model will be run on a composite of the two meshes shown in Lynch et al. 1997.
The seaward open ocean boundary of the large scale mesh goes to a depth of about 2000 meters to be somewhat remote from the part of the Gulf's wind-forced response located on the continental slope (see Greenberg et al. 1997). The more refined coastal mesh will be embedded in the large scale mesh so that the details of the coastal sea level response to storm forcing can be resolved adequately.
To more accurately model the storm response of sea level in the coastal Gulf of Maine, we will:
1) Force the model with both space/time variable atmospheric pressure and wind stress
2) Account for the anomalous friction caused by the nonlinear interaction between surface waves and currents (Grant and Madsen 1979).
To simplify the diagnosis of new effects due to wave/current-induced bottom friction and nonlinearities, we will run the model with constant density. Our experiments will focus primarily on the late fall/winter/spring time periods, when storm-forced effects are strong and natural density stratification is relatively weak. Biological productivity rates are high during late winter/early spring, and the model will simulate realistic coastal ocean response during this important time of year.
There is increasing pressure on federal, state and local government agencies to find more effective tools for environmental hazard management because of:
1) Accelerated aquaculture development
2) Increased pollution of the coastal ocean and estuaries due to oil spills and other toxic inputs
3) A greater frequency in shellfish bed closures due to noxious phytoplankton blooms.
Although the complexity of the coastal ocean system poses great challenges to such developments, recent research results are providing direction to such efforts. It now appears that coastal ocean management tools of the future will consist of seamlessly blended suites of atmospheric, ocean, estuarine and ecosystem models, all fed by the necessary operational observations via distributed data and information management systems. Specially packaged sets of observations, model outputs and other information will be delivered in a timely and useful form to the desks of the appropriate environmental managers.
Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant
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