[MITgcm-support] mitgcm seaice

[Martin Losch]

Hi Mike,

the non-zero drag used to be necessary to have a non-singular system matrix for the solver also where there there is no ice.

In a more recent version of the code I added a runtime parameter SEAICEdWatMin, which defaults to 0.25. This value can be set to zero, and the model should still run. After different (older) changes it is not longer required that there’s a minimum drag.

I am not sure about checkpoint 67c, but you can most likely reduce 0.25 to a much smaller value, if necessary. 

Martin


> On 23. Nov 2022, at 21:01, Jinlun Zhang <jlzhang at uw.edu> wrote:
> 
> Hi Mike,
> 
> The 0.25 value is used to prevent water drag from being too small in order to avoid possible instability. Water drag is often higher than 0.25, so the insensitivity might not come from this. Otherwise, the ice V or ocean V might be a bit too small.
> 
> Cheers,
> 
> Jinlun
> 
> On 11/23/2022 9:02 AM, Michael A Spall wrote:
>> Hi All,
>> I am doing a problem with the MITgcm and the seaice package. The results are nearly insensitive to the value of SEAICE_waterDrag.
>> I see in the code that if a certain condition is met then the drag is set to 0.25, which I suspect is being met in my calculations (I am
>> checking this).  Can someone explain the reasoning behind this limit?
>> 
>> from MITgcm_c67c, seaice_oceandrag_coeffs.F:
>> 
>>            IF ( SEAICE_waterDrag.LE.0. ) THEN
>>             CwatC(I,J,bi,bj)=0.
>>            ELSEIF ( TEMPVAR.LE.(0.25 _d 0/SEAICE_waterDrag)**2 ) THEN
>>             CwatC(I,J,bi,bj)=0.25 _d 0
>>            ELSE
>>             CwatC(I,J,bi,bj)=SEAICE_waterDrag*SQRT(TEMPVAR)
>>            ENDIF
>> 
>> Thanks,
>> Mike
>> 
>> ==================================================================
>> 
>> Michael A. Spall
>> Senior Scientist
>> Clark 323A
>> Department of Physical Oceanography
>> Woods Hole Oceanographic Institution
>> 360 Woods Hole Road MS #21
>> Woods Hole, MA 02543
>> 
>> 508-289-3342
>> mspall at whoi.edu
>> https://urldefense.com/v3/__https://www2.whoi.edu/staff/mspall__;!!K-Hz7m0Vt54!nS_Dw_xQpzrotMZ2-NkZZ2MwbO4ort_7yY9DyiMC6iuck-GyACH2psYlBuH2mbOXELbNedtpD81SnnU$
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> https://urldefense.com/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!K-Hz7m0Vt54!nS_Dw_xQpzrotMZ2-NkZZ2MwbO4ort_7yY9DyiMC6iuck-GyACH2psYlBuH2mbOXELbNedtp8fziL7Q$
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support