[MITgcm-support] noise in high resolution run

[Martin Losch]

Hi,

I seem to have a problem with a 1/6 by 1/6*cos(phi) run with open  
boundaries. The domain is the Drake Passage. A plot of bathymetry and  
velocities can be found in
http://mitgcm.org/~mlosch/noise.png

Whatever friction parameters I have tried (viscAh=1e0 to 2e1 and  
viscA4=1e8 to 4e10, and similar for diffusivities, I also tried the  
Leith/Smagorinski variants), I seem to get noise in the north western  
part of the domain. What worries me is, that
1. The noise seems to propagate (compare day 149 to day 214 in the  
bottom panels of the figure)
2. The noise seems to be mainly in the x-direction

I use mom_fluxform. For mom_vecinv the problem is there, too.
I use USE_ISOTROPIC_SCALING (for viscosities because my y-grid varies  
with y) and do not use COSINEMETH_III (although that probably doesn't  
make much of a difference). When I turn off USE_ISOTROPIC_SCALING,  
the noise is still there, but the x-alignment is slightly less  
obvious (although very much present). If the noise were deltaX in  
both directions, I would be concerned about my friction parameters.  
Here I suspect a problem in the viscosity implementation, but I  
cannot see how and were.
There is some noise that is produced by the open boundaries, but that  
usually goes away. I think that the generation of the noise is  
connected to the topography around the tip of South America

I wonder if anyone has seen something like this before. What do you  
think?

Martin