Hybrid vertical coordinate in the Bergen Layered Ocean Model (BLOM)

A hybrid vertical coordinate, following the arbitrary Lagrangian-Eulerian (ALE) method, has recently been implemented in the Bergen Layered Ocean Model (BLOM), which is the ocean component of the Norwegian Earth System Model (NorESM). A suitable regridding approach and accurate remapping is crucial for the application of the ALE method for ocean climate modelling. The steps taken in BLOM for high-order polynomial reconstruction of variables on the source grid builds on the approach of White and Adcroft (2008); White et al. (2009), but extended with a novel non-oscillatory limiting method that improve accuracy at smooth extrema and techniques to handle numerical issues associated with highly variable cell widths. The ALE method in BLOM has been tested with different vertical grids such as constant pressure levels and a hybrid level/isopycnic grid. The latter nudges layer interfaces to approach reference densities at interfaces (continuous isopycnals) with minimum layer thicknesses enforced at the upper boundary to facilitate resolution in the planetary boundary layer. In addition to describing the ALE approach in BLOM, the adaption of physical parameterizations and experience from forced and fully coupled simulations will be presented.