[MITgcm-support] Prescribing Constant 4°C Temperature in Idealized Lake Margins Throughout Simulation

[Fateme Sharifi]

Dear MITgcm Community,

I am currently working on a MITgcm model of a lake with a Gaussian-shaped
bathymetry and a 3D lake mask. I have encountered an issue where some wet
points still have temperature (T) and salinity (S) values equal to zero.

In my setup, I have defined an RBCS mask overlaying the Gaussian-shaped
shallow region of the lake. The RBCS temperature files currently have zero
values outside the RBCS mask, and only the shallow RBCS areas are set to
4 °C. All wet points outside the RBCS region are left free to evolve,
ensuring that the interior of the lake is not artificially constrained.

I would like to clarify whether it is necessary to define the RBCS mask
over the entire lake, or if it is sufficient—and indeed better—to define it
only in the shallow regions where restoring is desired (i.e., the moat/top
slab) to maintain 4 °C.

Any guidance or recommendations on best practices for applying RBCS in such
a lake setup would be greatly appreciated.

Thank you very much for your time and help.

Best regards,
Fatemeh Sadat Sharifi
Ph.D. Candidate at
The Leibniz Institute of Freshwater
 Ecology and Inland Fisheries (IGB)


On Fri, Jul 4, 2025 at 2:55 PM Fateme Sharifi <fateme.sharifi1391 at gmail.com>
wrote:

> Dear MITgcm Support Team,
>
> I am currently working on an idealized model setup using MITgcm to
> simulate *seasonal ice-covered lakes*, with a focus on *moat formation*—ice-free
> lateral regions that remain at approximately 4 °C throughout the running
> period.
>
> In my setup, I represent an idealized freshwater lake with a *Gaussian-shaped
> bathymetry*. The lake is initialized with a *vertically stratified
> temperature profile*, ranging from 0 °C at the surface to 2 °C at the
> bottom in the interior. To simulate moats, I initialize a lateral zone
> along the lake boundary with a uniform temperature of *4 °C*,
> representing maximum freshwater density.
>
> My goal is to maintain this *lateral 4 °C moat temperature* fixed
> throughout the simulation period, while allowing the interior to evolve
> freely according to the model dynamics.
>
> I would appreciate any guidance on the following:
>
>    -
>
>    Is there a way to *prescribe a constant temperature* (e.g., via a
>    boundary condition or restoring term) in specific lateral grid cells (e.g.,
>    within a ~500 m wide margin)?
>    -
>
>    Would you recommend using *sponge layers*, *restoring zones*, or
>    another method for this purpose in the MITgcm framework?
>
> Thank you in advance for your support.
>
> Best regards,
> Fatemeh Sadat Sharifi
> Ph.D. Candidate at
> The Leibniz Institute of Freshwater
>  Ecology and Inland Fisheries (IGB)
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20250904/d36d5baa/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Y-Z Temperature + RBCS.jpg
Type: image/jpeg
Size: 129358 bytes
Desc: not available
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20250904/d36d5baa/attachment-0001.jpg>