[MITgcm-support] shelfice_thermodynamics.F crash

[Martin Losch]

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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