[MITgcm-devel] momentum OBCS implemetation

[Jean-Michel Campin]

Hi,

I did some changes last month (once again) in OBCS implementation for 
tracer, using maskInC,W,S in pkg/generic_advdiff/ S/R for all the 
wider-stencil scheme (assuming zero gradient beyond the OB), 
so that the calls to OBCS_COPY_TRACER (that I added last November !)
are no longer needed (just removed yesterday).

The main motivation for this is that it's cleaner (e.g., for biharmonic diffusion), 
the OB border-line can be more general (concave interior) with OB closer to 
each-other (Olx grid-points separation instead of 2xOlx) and it can be extended 
to the momentum whereas the OBCS_COPY_TRACER approach is more difficult for U,V.

Going to apply the same idea to the momentum, starting with biharmonic 
viscosity (& leaving the 4th Order coriolis for later).
In short, the changes are (like zero gradient beyond the OB):
- to multiply divergence (& tension) by maksInC
- to multiply horiz. grad of vorticity by maskInW/S
Additional changes are needed in mom_calc_visc.F (Leith & Smagorinsky)
but even the changes outside mom_calc_visc will already affects the computed 
viscosity. So I was going to check-in these changes all at once.