[MITgcm-support] global simulations and resolution

[Baylor Fox-Kemper]

Hi Martin,
   What are you doing about surface mixing?  I think folks at GFDL had 
some luck with Richardson number Criteria in tuning similar problems.
   Where is the deep water (AABW) forming?  How are the surface 
conditions there?  You might contact Bob Hallberg at GFDL for tips, he 
spent a lot of time getting the Hallberg model to work around the 
ACC...
   Cheers,
    -Baylor


On Sep 7, 2005, at 3:33 AM, Martin Losch wrote:

> Hi there,
>
> I am running a 4x4 degree global simulation (almost identical to the 
> verification experiment global_ocean.90x40x15) in parallel to a 2x2 
> degree global simulation (180x80x23). These simulations differ mainly 
> in their respective horizontal and vertical resolution. Of course, I 
> had (initally) friction parameters adjusted, so that viscAh=5e5 in the 
> 4x4-run became 5e4 in the 2x2 run.
> Both experiments use trenberth winds, ncep heat flux (short wave and 
> the rest), SST and SSS restoring to Levitus, GM, KPP, no seaice, no 
> Arctic ... All runs are integrated for 3000 years with asynchronous 
> time stepping (deltaTtracer=172800 for the 4x4 and 43200 for the 2x2 
> runs).
> The solutions are broadly similar in terms of circulation (the 4x4 run 
> is more sluggish, but I can tune the friction parameters so that they 
> give similar ACC transports, for example). What is really different 
> are the water masses, and I cannot see a way to make them agree more 
> closely:
> broadly speaking, in the 2x2-run: when compared to Levitus data, the 
> Southern Ocean (south off the ACC) is too cold and too salty. The deep 
> ocean (below 3000m) is far too cold. The 4x4-run is too cold and too 
> fresh below 3000m, but in the Southern Ocean theta is nearly OK, but 
> salinity is too low. (for pictures see 
> http://mitgcm.org/~mlosch/run2x2_ts.pdf and 
> http://mitgcm.org/~mlosch/run4x4_ts.pdf)
>
> I would like to know, how this difference can be explained, that is, 
> how I can tune either model (preferably the 2x2 degree model, because 
> is too cold) to be similar to the other. Is there any experience with 
> this out there? Is it possible that the vertical resolution in 
> combination with surface restoring is responsible for this difference 
> (the 4x4-top layer is 50m thick, whereas the  2x2-top layer only 
> 10m.)?
> Any suggestion is greatly appreciated.
>
> Martin
>
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