[MITgcm-support] shelfice_thermodynamics.F crash

[Dimitris Menemenlis]

Hi Martin, for time being I added your suggested modification to our local repo:
https://github.com/MITgcm-contrib/llc_hires/blob/master/trillium/llc_4320/code/shelfice_thermodynamics.F

But yes, I think this probably needs to make its way back to the main branch.
Will you take care of the PR?  Or shall I try to figure out how to submit one?

D.


> On Jan 21, 2026, at 1:04 AM, Martin Losch <Martin.Losch at awi.de> wrote:
> 
> Do you think that this should be a PR?
> 
> Martin
> 
>> On 20. Jan 2026, at 18:38, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:
>> 
>> Hi Martin, I just tested your modification below in my baby set-up and it works fine.
>> 
>> You just need to add a “-d 0” in "IF ( saltFreeze .EQ. 0. _d 0 ) THEN"
>> 
>> Thanks for quick response.
>> 
>> D.
>> 
>> P.S.: I still owe you a response for the “Supercooled waters” post.  I don’t know how you and Oliver and Jean-Michel are so efficient!
>> 
>> P.P.S.: Happy New Year and belated Merry Christmas to you and family.
>> 
>> 
>>> On Jan 20, 2026, at 5:37 AM, Martin Losch <Martin.Losch at awi.de> wrote:
>>> 
>>> Hi Dimitris and Kayhan,
>>> 
>>> great catch. I suggest a different fix: Even though it’s unlikely, we may want to allow saltFreeze=0. So If sLoc = 0, then we have freshWaterFlux = rUnit2mass * shiTransCoeffS(i,j,bi,bj) * ( 1. _d 0 - 0. / 0. ) and could drop the part in the parentheses, i.e.
>>> 
>>>             IF ( saltFreeze .EQ. 0. _d ) THEN
>>>              freshWaterFlux = rUnit2mass
>>>      &            * shiTransCoeffS(i,j,bi,bj)
>>>             ELSE
>>>              freshWaterFlux = rUnit2mass
>>>      &            * shiTransCoeffS(i,j,bi,bj)
>>>      &            * ( 1. _d 0 - sLoc(I,J) / saltFreeze )
>>>             ENDIF
>>> 
>>> What do you think? Does that work for you?
>>> 
>>> Martin
>>> 
>>>> On 20. Jan 2026, at 00:46, Dimitris Menemenlis <dimitris.menemenlis at sjsu.edu> wrote:
>>>> 
>>>> shelfice_thermodynamics.F can crash when the line
>>>>            saltFreeze = (- bqe - SQRT(discrim))*recip_aqe
>>>> returns 0, so that
>>>>            freshWaterFlux = rUnit2mass
>>>>     &           * shiTransCoeffS(i,j,bi,bj)
>>>>     &           * ( 1. _d 0 - sLoc(I,J) / saltFreeze )
>>>> returns NaN.
>>>> 
>>>> This appears to be a consequence of "sLoc(I,J)  = 0”
>>>> One possible fix is to add:
>>>>          sLoc(I,J) = MAX(salt(I,J,K,bi,bj), 0.1 _d 0)
>>>> 
>>>> >>>>>>>
>>>> 
>>>> Kayhan Momeni, from his ongoing llc4320 simulation has extracted all the model state variables
>>>> at the time step before (3205150) and during (3205151) the first NaN:
>>>> https://nasa-ext.box.com/s/5ah3cffma49vkvfwgjsown7ytgs8i5i1
>>>> 
>>>> I have created a small (17x17x173) regional set-up that (approximately) recreates this crash:
>>>> https://nasa-ext.box.com/s/varcd6iu3ilg44bzly9hnzee1wnigfod
>>>> https://nasa-ext.box.com/s/bpq9p9yksksdhgr2knofj9fsqj0ntv5x
>>>> https://nasa-ext.box.com/s/atgqgp43st6o4u4976gfr5not465zbdr
>>>> 
>>>> I have verified that the small set-up is able to reproduce the SHICE_fwFlux NaN, the white grid cell at center of:
>>>> https://nasa-ext.box.com/s/trhs4kd8vpt9tx4t8riq934olrks3h30
>>>> 
>>>> All of the above are under: https://nasa-ext.box.com/s/q4sx5w4bnwui4v1afec9k2kb41ejml3v
>>>> 
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