[MITgcm-support] surface treatment and resolution dependentinstability?

[钱钰坤]

Hi Jody,


One possible reason may be that as your grid gets larger, you need to increase the viscosity to prevent energy accumulating at grid scale.


PS: Previous experience tells me that if you turn on rigidLid (rigidLid=.TRUE.), the overall time for the integration will increase significantly (compared to rigidLid=.FALSE.).  I've known idea why this should be the case.


------------------
 Best regards 
 
Yu-Kun Qian (钱钰坤) 
Center for Monsoon and Environment Research 
 Department of Atmospheric Sciences
School of Environmental Science and Engineering 
 Sun Yat-sen University 
No. 135 Xingang West Road, Haizhu District 
Guangzhou, 510275, P.R. China 
Tel; 020-84115227 
Email: qianyk at mail3.sysu.edu.cn      


 
 
 
------------------ 原始邮件 ------------------
发件人: "Jody Klymak"<jklymak at uvic.ca>;
发送时间: 2017年4月27日(星期四) 上午6:25
收件人: "mitgcm-support"<mitgcm-support at mitgcm.org>; 

主题: [MITgcm-support] surface treatment and resolution dependentinstability?

 

Hi all,

Just trying to educate myself…

I am running a doubly-periodic domain with some the only external forcing a body force applied to keep the flow moving. The domain is 4000 m deep, with dz=10 m.  Hydrostatic simulations...

I had as my surface conditions:

rigidLid=.TRUE.,
implicitFreeSurface=.FALSE.,
exactConserv=.FALSE.

and this ran fine at 100-m horizontal resolution, and 1000-m.  

Without changing anything about the simulations, except moving to 2000-m, the solution would blow up after a few time steps.  In particular I noticed that `dynstat_eta_mean` would start increasing (or decreasing) before any of the CFL criteria seemed to be going bad.   With that clue in mind I found that:

rigidLid=.FALSE.,
implicitFreeSurface=.TRUE.,
exactConserv=.FALSE.

seems stable.

1) Is this instability something thats known?  It seems non-intuitive to me that as dx,dy gets larger the instability grows.
2) What are the consequences of rigid lid versus implicit free surface? Is there a good primer on choosing these?  I’m ashamed to say that I have simply plugged along w/ the same values for years w/o really questioning them.

Thanks a lot,   Jody

--
Jody Klymak    
http://web.uvic.ca/~jklymak/






_______________________________________________
MITgcm-support mailing list
MITgcm-support at mitgcm.org
http://mitgcm.org/mailman/listinfo/mitgcm-support
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20170427/0ab8cb3a/attachment.htm>