[MITgcm-support] shelfice_thermodynamics.F crash

[Dimitris Menemenlis]

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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