[MITgcm-support] Solution blows up

[Jody Klymak]

This is too high for timestep=0:

(PID.TID 0000.0001) %MON dynstat_wvel_max             =   6.4849491655418E-03
(PID.TID 0000.0001) %MON dynstat_wvel_min             =  -1.0465307563404E-02

%MON advcfl_wvel_max              =   6.8697658345833E-01

Again, its possible this would settle down after a while and you can increase the timestep later in the run.  

As Matt says, you may just have interpolated some velocities inconsistently since this is appearing in the first time step (so the T and S interpolation don’t even entre into the problem).  It also may simply bet hat your vertical resolution is what is limiting your timestep.

Cheers,   Jody

> On 4 Mar 2020, at 09:18, Matthew Mazloff <mmazloff at ucsd.edu> wrote:
> 
> Its due to how you interpolate 1/12 to 1/6. You have to use caution.
> Do the 1/6 and the 1/12 have the same number of z levels? If not you have to use caution here. LIkely interpolate in horizontal and then in depth. As you go down extrapolate deeper in a stratification stable way.
> 
> Some notes
> - Obviously there can be no extrapolation from land, and I assume you did that correct. 
> - I would not fill with defaults at depth - this is possibly your problem - why do you even get blanks as I would assume the 1/12 would have at least 1 of its four grid cells in the 1/6 wet cell. Try bin averaging the 1/12 to the 1/6
> 
> -Matt
> 
> 
> 
> 
>> On Mar 4, 2020, at 8:55 AM, Shevchenko, Igor <i.shevchenko at imperial.ac.uk> wrote:
>> 
>> Hi Jody,
>> 
>> Thank you very much for your answer.
>> Attached is STDOUT.0000 . Does the CFL look suspicious?
>> 
>> Best regards,
>> Igor
>> 
>> ________________________________________
>> From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Jody Klymak <jklymak at uvic.ca>
>> Sent: 04 March 2020 16:44
>> To: mitgcm-support at mitgcm.org
>> Subject: Re: [MITgcm-support] Solution blows up
>> 
>> 
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>> Hi Igor,
>> 
>> 1. you could have density overturns in the interpolated field, and those will manifest as high vertical velocities that violate the CFL criterion.
>> 
>> 2. you likely have some fast adjustment that is violating CFL and may need to use a smaller timestep for a little while until the model adjusts.
>> 
>> The fact you tried “different time steps” says that maybe the problem is more complicated, but it would be good to look at STDOUT.0000 and see what the cfl criterion is saying.
>> 
>> Cheers,   Jody
>> 
>> --
>> Jody Klymak
>> http://web.uvic.ca/~jklymak/
>> 
>> 
>> 
>> 
>> 
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--
Jody Klymak    
http://web.uvic.ca/~jklymak/