[MITgcm-support] [EXTERNAL] Re: shelfice_thermodynamics.F crash

[Fenty, Ian G (US 329B)]

Martin and Dimitris,

I may have missed this if the discussion, but if the ocean salinity is zero and the salinity of the ice is zero, then the assumptions of the three-equation model break down. In that case, there is no boundary layer at the ocean/ice interface. The melting expression simplifies to

Step 1, find the local melting point:
      T_f = c_0 + b_0 p

Step 2, calculate the heat flux to the ice
      <w’T’> = \gamma_T (T_o - T_f)

Step 3, calculate the freshwater flux from melting:
Case a: no heat conduction through the ice
      \rho_w c_{\pw}  <w’T’> = -Lq

Case b: heat conduction through the ice
      \rho_w c_{\pw}  <w’T’> + \rho_i c_{pi}  \kappa_i (T_i - Tf_f) D_i = -Lq

q is the ice mass flux [kg s-1 m-2], which can be expressed in terms of velocity of water meltwater coming into the ocean (w_b) as
q = \rho_w_b

But yea, it’s hard to imagine the case where the model comes up with a solution of S_b = 0 in the original three equation model.
It can only happen if the heat transfer coefficient is infinite, if the salinity diffusion is zero, or the ocean salinity is zero.
If your ocean salinity is going to zero, it suggestions a different problem. Maybe a numerical artifact (undershoot/overshoot).

I attached my three-equation model notes.  From page 3 on the variable names (the epsilons) are from the shellfire code (or at least some older version of it)

Ian



From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Martin Losch <martin.losch at awi.de>
Date: Thursday, January 22, 2026 at 10:43 PM
To: mitgcm-support at mitgcm.org <mitgcm-support at mitgcm.org>
Subject: [EXTERNAL] Re: [MITgcm-support] shelfice_thermodynamics.F crash

I don’t know. If both solutions give the same results, I’d go with SHELFICE_USE_HEATBALANCE_FOR_FRESHWATERFLUX defined, as this is in compact form what is implemented in pkg/steep_icecavity. I have no experience with this version. The other option is a hack that just avoids the division by zero, this is only physically correct if sLoc is really zero at the same time.

M.

On 22. Jan 2026, at 21:05, Dimitris Menemenlis <dimitris.menemenlis at sjsu.edu> wrote:

Done.  I left a review.  Both options work.
Which one do you recommend that Kayhan and I use?
with or without SHELFICE_USE_HEATBALANCE_FOR_FRESHWATERFLUX defined?

Thanks a million for super-quick turnaround on this request.

D.


On Jan 22, 2026, at 4:58 AM, Martin Losch <Martin.Losch at awi.de> wrote:

Please have a look at PR #968
https://github.com/MITgcm/MITgcm/pull/968<https://urldefense.us/v3/__https://github.com/MITgcm/MITgcm/pull/968__;!!PvBDto6Hs4WbVuu7!NJMtDwoC-xNdirXVV-Z-UZfpysl7_c7oQrii5iuN41ypBQpoyGEGyCxwEQZW9w2OcmeUGO-LgP7acoh3NpYJVPbeiTE$>

@Dimitry, it would be great, if you could try this code in your little test, and also review it in github.

M

_______________________________________________
MITgcm-support mailing list
MITgcm-support at mitgcm.org
http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<https://urldefense.us/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!PvBDto6Hs4WbVuu7!NJMtDwoC-xNdirXVV-Z-UZfpysl7_c7oQrii5iuN41ypBQpoyGEGyCxwEQZW9w2OcmeUGO-LgP7acoh3NpYJuh3-YM0$>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20260123/f203d72a/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Three equation model v9.pdf
Type: application/pdf
Size: 262132 bytes
Desc: Three equation model v9.pdf
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20260123/f203d72a/attachment-0001.pdf>