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Real-time forecasting of wave conditions in a coastal bay
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Numerical simulations of wave conditions in a coastal bay using the nearshore wave model SWAN are presented. The field site is Lunenburg Bay, a coastal embayment on the southern shore of Nova Scotia approximately 8 km long and 4 km wide. It has irregular bathymetry characterized by a typical depth of 10 m and is exposed to wave energy from the North Atlantic Ocean. Surface wave observations have been collected at various locations in the bay since 2002. Validation of the model is presented for two events with large swell and strong winds, and predicted wave spectra are compared with observations inside the bay. Hurricane Juan, Sept. 2003, had offshore significant wave heights up to 9 m and Extra-Tropical Storm Nicole, Oct. 2004, had wave heights up to 4 m. The relative importance of physical processes including refraction, whitecapping, bottom friction and wave breaking are compared at several locations. Two whitecapping dissipation expressions have been used, including a newly proposed spectrally local expression. The new expression has an improved prediction of the wind-sea portion of the wave spectrum, especially in the presence of swell. For 2007, the model is used for real-time forecasting of wave conditions in the bay, with forecast predictions of offshore waves, winds and water levels as inputs. Offshore wave conditions are generated using GEM-global (1 degree) wind forecasts to force the Wave Watch III model over the North Atlantic. A series of nested grids bring the waves to the boundary of Lunenburg Bay. The SWAN model is run for the bay using these boundary conditions, in addition to GEM-regional (15 km) wind forecasts and tidal water level predictions. Inside the bay, the forecast nearshore wave conditions are compared to real-time observations. Particular attention is paid to both incoming swell and locally-generated wind sea peaks in the wave spectra.
Mulligan, R., A. Hay, and T. Bowen. "Real-time forecasting of wave conditions in a coastal bay." Canadian Meteorological and Oceanographic Society, McDonald Building 150 Louis Pasteur, Ste 112 Ottawa, ON, K1N 6N5 Canada. [np]. CMOS Congress 2007 - Air, Ocean, Earth and Ice on the Rock, St. Johns, Newfoundland and Labrador, May 28 - June 1, 2007.