[MITgcm-support] timestep

[Göran Broström]

Dear Support

In most model experiments I have considered I have always been surprised how short time step I have to take to avoid the model to blow up. As far as I can tell the fields are not even close to be at the point of being numerically unstable (i.e., dt/dx<<1). Especially during long integration this has been a problem. 

I have for some time suspected that it has something to do with the vertical velocity but I have not been able to confirm that. Anyway, I saw that there is an option for taking implicit vertical advection (Implvertadv). Is there anyone who have had the same problem and solved it using the implicit vertical advection? I have looked around at the model examples but I have not seen that it is used so I am somewhat uncertain to use it.

Any other suggestions?


sincerely
Göran Broström

Ps. I guess that I can always use stronger diffusion but that is something I want to avoid.
Ps2 I have to confess that I have not upgraded to the latest model version until a few days ago. Perhaps the new version is more "stable".
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