The primary dissipation mechanisms for global tides are boundary layer dissipation and internal tide dissipation from barotropic to baroclinic tidal conversion (Munk, 1997). From early estimates of total tidal dissipation characterized solely by boundary layer dissipation by Taylor andShaw (1920) andJeffreys (1921) to sophisticated estimates using altimeter data and assimilated tidal models performed by Egbert and Ray (2001) and Green and Nycander (2013), our understanding of where the astronomical energy imparted on the oceans is dissipated has grown tremendously. While there is some uncertainty in where tidal dissipation predominantly occurs in nature, it is relatively well accepted that tides dissipate approximately 3.5 TW of energy (Munk, 1997). What is more unclear is the distribution between internal tide dissipation and boundary layer dissipation. Munk (1997) estimates 2.6 TW of dissipation on the shelves and 0.9 TW dissipated through internal tides. Egbert and Ray (2001)

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This paper describes a 2D-3D hybrid model for tsunami simulations that uses an overlapping method based on an arbitrary grid. A 2D model is used to simulate wave propagation from the source area to the offshore area, and a 3D model is then used to simulate the free surface flow around structures in coastal areas. An overlapping method that satisfies the conservation and compatibility conditions is developed to couple the two models. The shallow water equations are applied for the 2D model, and the Navier-Stokes equations and continuity equations are applied for the flow field of the 3D model. The Allen-Cahn equation is applied for the interface-capturing method of the 3D model. The stabilized finite element method is applied for the spatial discretization and the Crank-Nicolson method is used for the temporal discretization of the governing equations. The model is verified and validated through several numerical analysis examples.

Western Alaska regularly experiences storm surge events induced by extra-tropical storms, most active during fall, winter, and spring. Among others, the presence of sea ice in Western Alaska seawater poses a challenge in modeling storm surge in this area. Existing storm surge models rarely consider sea ice effects together with wind-induced wave effects. In this paper, we present an ALaska Coastal Ocean Forecast System (ALCOFS) which considers sea ice and wave effects for a real time storm tide forecasting. The system is based on a tightly coupled ADCIRC (a hydrodynamics model used widely for tide and storm surge modeling based on shallow water equations) and SWAN (wind wave model governed by spectrum action balance equation). The sea ice effect is included by incorporating a parameterization of air-sea-ice drag in the ADCIRC storm surge model, and of the wave energy dissipation caused by sea ice is considered in SWAN. The model utilizes an unstructured mesh with variable resolution (ranging from 20km to 70m) to achieve accurate predictions and fast run times. The model was exercised carefully with tidal tests to obtain good quality of tidal results and the optimized parameter setups. The impact of sea ice and waves was examined with several storm surge events. In addition, a three year long storm surge hindcast has been conducted to test the model robustness and to examine the sea level variation trends. Furthermore, an efficient real time continuous storm tide, wave and surge forecasting scheme which performs a cycle with a one day nowcast and then a five day forecast is proposed. The performance of the forecasting system is demonstrated and evaluated through a year long forecast. To examine the effectiveness of the forecasting scheme, it is demonstrated through the SWAN+ADICRC and stand alone WAVEWATCH III (WWIII) models. The recorded forecast results for the past show good performance by comparing with observations. This paper underscores the importance of incorporating sea ice and wave effects into simulations of storm surges for the area with sea ice conditions, and presents the skill of the forecasting system.

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