Unresolved issue:
Advection term, gradient should operate on velocity, not mass transport!


2012-07-12:
Checkerboard due to advection, imminent catastrophe.
The method was NONLIN=7, i.e. the formula uses  (Grad) M/H
(NONLIN=2 or 3: (M/H·Grad) M )

Have a look at the instruction file with which this was produced.
We had already reduced the time interval to 0.6 subcritical. Eddy viscosity is not low. Depth is changing dramatically there, however.
Here's the advection term's x-component:

B.t.w. at the boundaries the advection term was formulated according to nonlin 2 (3)

2012-07-11:
otemt1 did not step far
otem92 did not copy the UPD option from tide to tide, it rather reset it to a default 'NNY' or 'NYY'. This implied that user update was only included in the Active-boundary data set for the M2. otem92 did not fail on this condition, nor did otem16, only otemt1's watchdog began to bark and bite.
The offending values were  999. × √2.
It was helpful to set the bite_wd level in otemt1 very high and sample the elevation grid with the mouse.
It was even more helpful to send  OC ^A  in order to trace the active boundary calculation.

Remedy:
otem92 copies the previous UPD option now (unless another 'UPD:' option is found on the tide line.)
otem92 will stop on missing data at an active boundary. A stop message is sent to STDERR

2012-07-11:
Big elevation difference at an active boundary.
Reason: Eddy viscosity parameter too high.
Remedy:
With Fricp(4) = 5.e3 the difference was much less bold.

2012-07-10, FRIH:
otemt1 bombed at the southern coast of the Seattle strait, near that cape. In running up to the catastrophy a checkerboard pattern was developing.
Remedy:
Straight passive-boundary formulation of the advection term seemed to have had errors. Determination of the upwind grid offset must be done differently for these boundaries. Seemed to have helped.

2012-07-10:
Wrong conclusion. The checkerboard pattern was first thought to originated due to a sign error in the eddy viscosity term. What happens when you attack the bull at both horn and tail is that you think the horns has stabbed you while it was only the tail that slapped into your face.
No, the eddy term was o.k., the straightening of the advection term made all the change.




Appendix

2012-07-11 User update KATT/itoz-upd.dat
provides lines for copying tide information into parts of the active boundary where the global model has land nodes.
otem92b.ins namelist:
 itoz_upd_u=21
 qrwd_itoz_upd_u=.true.
 itoz_opt='YNN'
Open-file block:
21 B KATT/itoz-upd.dat