dimensionality of grid/mesh for data exchange

[RupertGladstone]

Data are currently exchanged between the OM and ISM on a 2d grid/mesh in 2d space. In reality the exchange occurs on a surface (well, leaving aside "mushy" layers...) in 3D space. ESMF is capable of allowing us to use 2D grids/meshes in 3D space, but using this would increase complexity of the regridding operations.
The vertical coords of the grid would need to be updated during the run.
The regridRouteHandle (an ESMF object currently created only during initialisation) would also need to be updated during the run.
How bad is the current simplification? Is it good enough that we don't need to implement the third dimension?