An unstructured-grid, nonhydrostatic, GVC ocean model Part I: Model description and application of vertical hybrid coordinates to internal solitary waves
We present a nonhydrostatic ocean model with a horizontally unstructured, C-grid and a moving, generalized vertical coordinate (GVC) designed for the simulation of nonhydrostatic processes in realistic ocean domains. The GVC system can represent any of the well-known z-level, terrain-following, or isopycnal coordinates while also being able to employ hybrid vertical coordinates. In this paper we outline the specific steps needed to incorporate the GVC system into the unstructured, C-grid, nonhydrostatic, z-coordinate SUNTANS model of Fringer et al. (2006). The approach is adapted from the nonhydrostatic, isopycnal-coordinate method of Vitousek and Fringer (2014), yet our model differs from that implementation through the development of a conservative momentum advection scheme and a positivity-preserving layer height scheme for horizontally unstructured grids. We validate the momentum advection implementation with simulations of a turbulent channel flow and demonstrate the advantages of the hybrid vertical coordinate approach over z- or terrain-following coordinates through simulations of internal solitary waves and the associated bottom boundary layer instability.