[MITgcm-support] MITgcm-support Digest, Vol 274, Issue 1

Thu Apr 16 07:32:47 EDT 2026

Hi Martin,

Thank you for your response and for sharing the RBCS documentation.

I understand that pkg/rbcs is useful for restoring the model fields toward
observations, and I have observed that it significantly improves the
representation of surface currents and mesoscale variability. However,
since RBCS effectively nudges the model toward prescribed fields, I feel
that such a setup is more suitable for state estimation and may limit its
applicability for sensitivity experiments (e.g., testing the impact of
salinity or freshwater fluxes or lateral fluxes like biogeochemical tracers
boundary forcing), as the relaxation tends to suppress the model’s
intrinsic variability.

In this context, I was considering whether adjoint-based methods (via
pkg/ctrl and the cost function framework) could be a better alternative. My
understanding is that, unlike RBCS, the adjoint approach adjusts initial
conditions and forcing fields so that the model naturally evolves toward
observations, thereby preserving the physical response of the system.

Could you please clarify whether such an adjoint-based setup would be
appropriate for conducting sensitivity studies in a regional/coastal
configuration? If so, I would appreciate any guidance or references on
implementing this approach within MITgcm.

Thank you again for your time and suggestions.

Kind regards,
Rajesh Killampalli
PhD Student

On Tue, Apr 7, 2026 at 9:30 PM <mitgcm-support-request at mitgcm.org> wrote:

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> Today's Topics:
>
>    1. How to restore the surface currents for accurate simulation
>       of submisoscale eddies. (Killampalli Rajesh)
>    2. Re: How to restore the surface currents for accurate
>       simulation of submisoscale eddies. (Martin Losch)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 7 Apr 2026 11:13:19 +0530
> From: Killampalli Rajesh <rajesh70530 at gmail.com>
> To: mitgcm-support at mitgcm.org
> Subject: [MITgcm-support] How to restore the surface currents for
>         accurate simulation of submisoscale eddies.
> Message-ID:
>         <CAPQY=hmSRgndSCzfF=
> q70KhQ7jf6hxOwtufys591YPtPEqy5TA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Dear MITgcm Support Team,
>
> I am running a regional MITgcm simulation (~3 km resolution) with
> time-varying GLORYS boundary conditions (U, V, T, S, SSH). I observe bias
> in surface currents (magnitude and direction), and mesoscale/submesoscale
> eddies are not well captured in the interannual simulations.
>
> I initially considered applying relaxation (nudging) the SST and SSS (e.g.,
> via climatological relaxation or using boundary-driven constraints in
> data.obcs). However, I understand that this not improving in the surface
> currents.
>
> I am considering whether surface current nudging (similar to SST/SSS) is
> possible or advisable. Specifically:
>
>    - Can pkg/ctrl be used to weakly/daily constrain surface currents or
> SSH?
>    - Is there any recommended approach to improve surface currents without
>    suppressing eddies?
>
> Any guidance would be appreciated.
>
>  Kind regards
>
> ```````````````````````````````````````````````
>
>  Killampalli Rajesh (Research Scholar)
>
>  Centre For Atmospheric Sciences,
>
>  Indian Institute of Technology, Delhi
>
>  Hauz Khas, New Delhi - 110016
>
>  O-Email: asz238484 at iitd.ac.in
> <rajesh93.cstaff at iitd.ac.in>
>
>  P-Email:  rajesh70530 at gmail.com <rajesh93.cstaff at iitd.ac.in>
>
>  Phone: +91 9492068095.
> ```````````````````````````````````````````````
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> Message: 2
> Date: Tue, 7 Apr 2026 12:05:36 +0200
> From: Martin Losch <Martin.Losch at awi.de>
> To: MITgcm Support <mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] How to restore the surface currents for
>         accurate simulation of submisoscale eddies.
> Message-ID: <7102EB37-9B63-40F3-8A80-89B593A95013 at awi.de>
> Content-Type: text/plain; charset="utf-8"
>
> Hi Killampalli,
>
> you can use pkg/rbcs for that, there?s even some documentation:
> https://mitgcm.readthedocs.io/en/latest/phys_pkgs/rbcs.html
>
> pkg/ctrl cannot be used for restoring.
>
> Martin
>
> > On 7. Apr 2026, at 07:43, Killampalli Rajesh <rajesh70530 at gmail.com>
> wrote:
> >
> > Dear MITgcm Support Team,
> >
> > I am running a regional MITgcm simulation (~3 km resolution) with
> time-varying GLORYS boundary conditions (U, V, T, S, SSH). I observe bias
> in surface currents (magnitude and direction), and mesoscale/submesoscale
> eddies are not well captured in the interannual simulations.
> >
> > I initially considered applying relaxation (nudging) the SST and SSS
> (e.g., via climatological relaxation or using boundary-driven constraints
> in data.obcs). However, I understand that this not improving in the surface
> currents.
> >
> > I am considering whether surface current nudging (similar to SST/SSS) is
> possible or advisable. Specifically:
> >
> > Can pkg/ctrl be used to weakly/daily constrain surface currents or SSH?
> > Is there any recommended approach to improve surface currents without
> suppressing eddies?
> > Any guidance would be appreciated.
> >
> >  Kind regards
> >
> > ```````````````````````````````````````````````
> >
> >  Killampalli Rajesh (Research Scholar)
> >
> >  Centre For Atmospheric Sciences,
> >
> >  Indian Institute of Technology, Delhi
> >
> >  Hauz Khas, New Delhi - 110016
> >
> >  O-Email: asz238484 at iitd.ac.in
> >  <mailto:rajesh93.cstaff at iitd.ac.in>
> >  P-Email:  rajesh70530 at gmail.com <mailto:rajesh93.cstaff at iitd.ac.in>
> >  Phone: +91 9492068095.
> >
> > ```````````````````````````````````````````````
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support
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> End of MITgcm-support Digest, Vol 274, Issue 1
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