[MITgcm-support] shelfice_thermodynamics.F crash

[Martin Losch]

I’ll take care of it.
M

> On 21. Jan 2026, at 19:49, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:
> 
> 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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>>>> 
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