[MITgcm-support] EVP stability

[Matthew Mazloff]

Hi Dimitris,

As you said, for her EVP model Hunke used 30s time-step with grid  
spacing 16km....at 1/6 deg. resolution my min spacing is  
3.8km...about 1/4 this..so I tried 7.5 sec timesteps and the model  
blew up on the third timestep.  Very unstable.  I have a 4x2 test  
setup and I ran EVP fine on this so I don't think its a bug in the  
configuration.  Could it be possible that EVP is just not stable at  
these resolutions?  Any advice?  Should I make a small high- 
resolution test setup?  Or does anyone else have one?

Thanks
-Matt




On Jan 27, 2007, at 9:36 AM, Dimitris Menemenlis wrote:

> Matt, stability criterion for EVP solver depends on internal ice  
> pressure, strain rates, a damping parameter for the elastic waves,  
> and other such things.  So it's not easy to compute explicitly.
>
> In "Journal of Computational Physics 170, 18–38 (2001)", Elizabeth  
> Hunke used a time step of 30 s for a domain with horizontal grid  
> spacing of 16 km.  So 45 s for your 1/6-deg domain seems too  
> large.  What is your smallest horizontal grid spacing, 4 km?  I  
> suggest that you try a 5-s to 10-s time step.
>
> Dimitris
>
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