[MITgcm-devel] heff_max...more sea ice issues

[Matthew Mazloff]

Dimitris and Jinlun,

Thank you very much for the info.  I will try some runs (in early  
January) and let you know how how things work out.

-Matt

On Dec 21, 2006, at 6:47 PM, Jinlun Zhang wrote:

>
>
> Matthew Mazloff wrote:
>
>> Thanks for the help...but I am a bit confused.  Two things
>>
>> 1) Re model efficiency and time stepping...I see there are 3   
>> parameters.  I am guessing  SEAICE_deltaTtherm should be the  
>> ocean  dynamics time-step as the forcing comes from this.  The  
>> other time  stepping parameters are  SEAICE_deltaTdyn  and  
>> SEAICE_deltaTevp which  I assume are the timesteps for each  
>> dynamic solver (LSR and EVP)  respectively.  And as I understand  
>> it LSR can use the "large"  timestep, but the EVP should use the  
>> "small" timestep...is this  correct?  And I am not using both at  
>> the same time obviously, but you  are saying I should try both  
>> independently because it is not obvious  which is faster.
>
> Correct.
>
>>
>> 2)More important than efficiency (right now anyway) is  
>> stability.   Jinlun, your first email seemed to suggest I try LSR  
>> with a half day  time step and LSR_ERROR=1e-4, or try EVP with  
>> "small" timestep.  Are  either of these methods likely to be more  
>> stable?
>
> Although we may use half day time step for LSR, but it is better to  
> use the same ocean dynamics time step for LSR for consistency, and  
> particularly when the code blows up. And using 1e-4. I would think,  
> from the heff_max figure, that the problem is most likely due to  
> the surface ocean stress calculation that causes instability.  
> However, you might also want to try EVP. I don't have much  
> experience with EVP, but people have been telling me that very  
> small time steps should be used for stability and for getting rid  
> of unphysical elastic waves. I read one paper about high-res.  
> (~10km) Hudson Bay simulation, the time step is as small as a few  
> seconds.
>
> Jinlun
>
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