[MITgcm-support] obcs_apply_ptracer

[ito at atmos.colostate.edu]

Hi Martin,

> if (i,j_obs) is an open boundary point, then (i,j_obs-1) is the first
> interior point. Only if both points are "wet" then maskS(i,j_obs) >
> 0; you can do this check too with maskC, but you'd have to check if
> maskC(i,j_obs) and maskC(i,j_obs-1) are > 0.

I noticed that obcs_apply_ptracer can introduce zeros into wet points (at
least it does to my runs) when S/W masks are equal to 0 on the boundary
but C mask is nonzero at the tracer point.  When I replace _maskS and
_maskW with maskC (of the tracer point), it does not introduce zeros into
wet points.

Consider a case near coastline where you have wet ob point at (i,j_obs)
but (i,j_obs-1) is on land. In this case maskS(i,j_obs) is zero and
obcs_apply_ptracer puts 0 into the wet boundary point.  When carbonate
chemistry solver is applied to the wet point with DIC=0, it produces NaN
leading to a crash.  So I think it would make more sense to use maskC for
tracer mask.

Taka