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

[Jinlun Zhang]

Matt,
This is a paper that gives a clue about EVP time step.
http://www.mrcc.uqam.ca/V_f/Publications/articles/Saucier2004_ClimDyn.pdf.
Jinlun

Matthew Mazloff wrote:

> 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
>>
>> _______________________________________________
>> MITgcm-devel mailing list
>> MITgcm-devel at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>
>
> _______________________________________________
> MITgcm-devel mailing list
> MITgcm-devel at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-devel


-- 

Jinlun Zhang
Polar Science Center, Applied Physics Laboratory
University of Washington, 1013 NE 40th St, Seattle, WA 98105-6698

Phone: (206)-543-5569;  Fax: (206)-616-3142
zhang at apl.washington.edu
http://psc.apl.washington.edu/pscweb2002/Staff/zhang/zhang.html