A HYbrid coordinate Parallel Ocean Program (HYPOP)
HYPOP is an ocean circulation model that is a hybrid in several ways, primarily in the vertical coordinate. The momentum equations continue to be solved on zcoordinates (depth as vertical coordinate), where the boundary conditions and pressure gradient are less problematic. For the tracer equations, HYPOP utilizes an Arbitrary Lagrangian Eulerian (ALE) scheme for the vertical coordinate. In an ALE scheme, the vertical coordinate moves in a Lagrangian way and a periodic remapping step allows the simulation to move to any (well, almost any) arbitrary vertical coordinate. Such a scheme allows the model to utilize depth as the vertical coordinate in the mixed layer while using a more Lagrangian (e.g. isopycnal) coordinate in the deep ocean.
Other algorithmic improvements (over the POP model) are also expected in this model, including a new remapping advection scheme and more advanced timestepping schemes. Most other software aspects of HYPOP will follow POP styles for performance and portability.

