[MITgcm-support] unrealistic model results in a regional model

[Matthew Mazloff]

Hi FL

Open boundaries are tricky.
It is possible you have very strong upwelling on them. Check this by looking at cross-sections. 

Maybe first see if it is your TS or UV by running with zeros UV prescribed.
If it is UV you may want to try leaving the tangential velocity to zero and only prescribing a normal velocity. 
(Prescribing tangential flow can be more trouble than it is worth.)
If it is the normal velocity you may want to make the bathymetry flat in the normal direction for several grid cells. 

Minor, but if your timestep is 45 seconds a restoring sponge of 1-5 days is weak. I don’t think this is you main issue, but you could reduce it to perhaps 0.5 - 1 days. 

Matt


> On Nov 25, 2025, at 5:38 AM, Fanglou Liao <fanglou.liao at unswalumni.com> wrote:
> 
> Dear MITgcm support
> 
> I am a new MITgcm user. I am building a regional ocean model with mitgcm, and have some problems with the model results, which I guess are associated with the open boundaries (East and South).  This model is of 0.03 deg, with initial (T, S, U, V) and open boundary conditions are interpolated from CMEMS reanalysis (0.083 deg). The external forcing are from ERA5. The Δt = 45 seconds. The model results are unrealistic, with small-scale patterns appear (attached), and the SST even dropped below 0 after a few days. When I closed the east and south boundaries, these problems disappeard.  Could you please kindly help me check my files attached and give me some advices? 
> 
> Thank you very much
> 
> FL
> <data><data.exf><data.obcs><data.pkg><model_SST_results.png>_______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org <mailto:MITgcm-support at mitgcm.org>
> https://urldefense.com/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!Mih3wA!DRepdlaYsgUf_Vexp5A95ALfhC-2CPOENiyOdNU96V7LOsCvz7tJbi1eaOAwiB_HM2YIVr6LFI--mTZKO7MWHgo2ifo$

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20251125/7b2bacad/attachment.html>