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

[Martin Losch]

Hi Fatemeh,

have a look at the RBCS package, pkg/rbcs, https://mitgcm.readthedocs.io/en/latest/phys_pkgs/rbcs.html

With this package you can restore 3D fields with arbitrary 3D masks. Via the mask you can also use regionally varying restoring timescales, i.e. the mask can have values between 0 (no restoring) to 1 (strongest restoring)

Setting the restoring timescale to the timestep is almost like prescribing the restoring temperature.

Hope that helps,

M

> On 4. Jul 2025, at 14:55, 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)
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