[MITgcm-support] Freshwater OBCS problem

[Dustin Carroll]

If the S forced at the E boundary is 1 less than the initial model values, it blows up on the first time step. My uvel is 0.1 m/s. Depth is 600m, with 35 cells. I have tried limiting the u velocities just to the upper layer, but that blows up as well.

I have a 100km telescoping sponge layer on each side (W,E) of my fjord channel. 

I am forcing the tides on the W boundary with no problems.

Has anyone tried forcing freshwater into the model through a OBCS? Can MITgcm handle this?

Cheers and thanks,
Dustin

> Well I don't get it. What if you make it s=35?  Maybe the model doesn't like the geometry of your channel?  Specified bcs work so you just go from a case that works until you break it.   Cheers.  Jody
> 
> --
> Jody Klymak
> http://web.uvic.ca/~jklymak
> 
> On 2012-12-22, at 13:24, Dustin Carroll <spanishcastlemagik at gmail.com> wrote:
> 
> > Hi Jody, 
> > Yes, it dies actually during the first time step. I do get negative salinities. I have tried changing my OBCS (river) S=1 psu and S=10 psu with the same results. It looks like my advection scheme is creating a undershoot. I have tried advection schemes 7,33,and 77 with the same results.
> > cg2d starts increasing positively from the start and then becomes NaN's. cg3d looks fine.
> > Yes, hopefully someone with experience with river or freshwater input will help out here as I am stuck on this.
> > 
> > Cheers,
> > Dustin
> >> 
> >> Does it die after one time step or one save step?  You can set your MonitorFreq to equal your time step to get diagnostics each step. I often set dumpFreq equal to my time step as well to save each step if I have something blow up early in the run. 
> >> 
> >> Any idea where your NaN's are? An uneducated guess would be that your salinities go slightly negative and the model doesn't accept negative salinity for some reason and NaN's those salinities.  Have you tried setting S=1 psu (or 10 psu) just to see if it can run for a while?  I don't think the advection scheme is up to keeping a zero salinity front strictly greater than zero.  
> >> 
> >> Good luck - hopefully someone else with experience putting a river into their model speaks up.
> >> 
> >> Cheers,   Jody

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