Abstract: About the application of an alternative approach for nonhydrostatic modelling to internal wave simulations



Authors: Knut Klingbeil, Hans Burchar

The increasing demand for the investigation of nonhydrostatic effects in ocean modelling requires serious modifications to traditional models applying the hydrostatic pressure assumption. Based on an explicit computation of the additional nonhydrostatic terms an alternative approach for the extension of hydrostatic ocean models will be presented. In contrast to classical approaches, the expensive inversion of huge algebraic systems can be avoided. If necessary, a cumulative temporal filter and an iteration procedure can be applied to improve stability.
Demonstrating the easy implementation of the alternative approach even into explicit mode-splitting models, the General Estuarine Transport Model (GETM), an efficient hydrostatic coastal ocean model, has been extended. Several numerical simulations, including standing basin waves, dispersing interfacial waves, lock-exchange and buoyancy-driven flows, have been performed. The results have been validated against analytical theory, laboratory experiments and other numerical simulations and indicate the feasibility of the alternative approach to simulate even strong nonhydrostatic regimes. For weak nonhydrostatic flows the alternative approach is expected to be more efficient than classical approaches.
Preliminary results of the simulation of internal waves in the Baltic Sea will be presented. These waves are usually generated by inflowing saline bottom currents in the lee of sills. Since their contribution to the mixing of the water column is crucial for the Baltic ecosystem, the numerical investigation of related transport and mixing mechanisms may help to fill the gaps in todays particularly poor knowledge.