<div dir="ltr"><div class="gmail_default" style="font-family:verdana,sans-serif"><p class="gmail-isSelectedEnd">Hi Martin,</p><p class="gmail-isSelectedEnd">Thank you for your response and for sharing the RBCS documentation.</p><p class="gmail-isSelectedEnd">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.</p><p class="gmail-isSelectedEnd">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.</p><p class="gmail-isSelectedEnd">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.</p><p class="gmail-isSelectedEnd">Thank you again for your time and suggestions.</p><p>Kind regards,<br>Rajesh Killampalli<br>PhD Student</p></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, Apr 7, 2026 at 9:30 PM <<a href="mailto:mitgcm-support-request@mitgcm.org">mitgcm-support-request@mitgcm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Send MITgcm-support mailing list submissions to<br>
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Today's Topics:<br>
<br>
1. How to restore the surface currents for accurate simulation<br>
of submisoscale eddies. (Killampalli Rajesh)<br>
2. Re: How to restore the surface currents for accurate<br>
simulation of submisoscale eddies. (Martin Losch)<br>
<br>
<br>
----------------------------------------------------------------------<br>
<br>
Message: 1<br>
Date: Tue, 7 Apr 2026 11:13:19 +0530<br>
From: Killampalli Rajesh <<a href="mailto:rajesh70530@gmail.com" target="_blank">rajesh70530@gmail.com</a>><br>
To: <a href="mailto:mitgcm-support@mitgcm.org" target="_blank">mitgcm-support@mitgcm.org</a><br>
Subject: [MITgcm-support] How to restore the surface currents for<br>
accurate simulation of submisoscale eddies.<br>
Message-ID:<br>
<CAPQY=hmSRgndSCzfF=<a href="mailto:q70KhQ7jf6hxOwtufys591YPtPEqy5TA@mail.gmail.com" target="_blank">q70KhQ7jf6hxOwtufys591YPtPEqy5TA@mail.gmail.com</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Dear MITgcm Support Team,<br>
<br>
I am running a regional MITgcm simulation (~3 km resolution) with<br>
time-varying GLORYS boundary conditions (U, V, T, S, SSH). I observe bias<br>
in surface currents (magnitude and direction), and mesoscale/submesoscale<br>
eddies are not well captured in the interannual simulations.<br>
<br>
I initially considered applying relaxation (nudging) the SST and SSS (e.g.,<br>
via climatological relaxation or using boundary-driven constraints in<br>
data.obcs). However, I understand that this not improving in the surface<br>
currents.<br>
<br>
I am considering whether surface current nudging (similar to SST/SSS) is<br>
possible or advisable. Specifically:<br>
<br>
- Can pkg/ctrl be used to weakly/daily constrain surface currents or SSH?<br>
- Is there any recommended approach to improve surface currents without<br>
suppressing eddies?<br>
<br>
Any guidance would be appreciated.<br>
<br>
Kind regards<br>
<br>
```````````````````````````````````````````````<br>
<br>
Killampalli Rajesh (Research Scholar)<br>
<br>
Centre For Atmospheric Sciences,<br>
<br>
Indian Institute of Technology, Delhi<br>
<br>
Hauz Khas, New Delhi - 110016<br>
<br>
O-Email: <a href="mailto:asz238484@iitd.ac.in" target="_blank">asz238484@iitd.ac.in</a><br>
<<a href="mailto:rajesh93.cstaff@iitd.ac.in" target="_blank">rajesh93.cstaff@iitd.ac.in</a>><br>
<br>
P-Email: <a href="mailto:rajesh70530@gmail.com" target="_blank">rajesh70530@gmail.com</a> <<a href="mailto:rajesh93.cstaff@iitd.ac.in" target="_blank">rajesh93.cstaff@iitd.ac.in</a>><br>
<br>
Phone: +91 9492068095.<br>
```````````````````````````````````````````````<br>
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<br>
Message: 2<br>
Date: Tue, 7 Apr 2026 12:05:36 +0200<br>
From: Martin Losch <<a href="mailto:Martin.Losch@awi.de" target="_blank">Martin.Losch@awi.de</a>><br>
To: MITgcm Support <<a href="mailto:mitgcm-support@mitgcm.org" target="_blank">mitgcm-support@mitgcm.org</a>><br>
Subject: Re: [MITgcm-support] How to restore the surface currents for<br>
accurate simulation of submisoscale eddies.<br>
Message-ID: <<a href="mailto:7102EB37-9B63-40F3-8A80-89B593A95013@awi.de" target="_blank">7102EB37-9B63-40F3-8A80-89B593A95013@awi.de</a>><br>
Content-Type: text/plain; charset="utf-8"<br>
<br>
Hi Killampalli,<br>
<br>
you can use pkg/rbcs for that, there?s even some documentation: <a href="https://mitgcm.readthedocs.io/en/latest/phys_pkgs/rbcs.html" rel="noreferrer" target="_blank">https://mitgcm.readthedocs.io/en/latest/phys_pkgs/rbcs.html</a><br>
<br>
pkg/ctrl cannot be used for restoring.<br>
<br>
Martin<br>
<br>
> On 7. Apr 2026, at 07:43, Killampalli Rajesh <<a href="mailto:rajesh70530@gmail.com" target="_blank">rajesh70530@gmail.com</a>> wrote:<br>
> <br>
> Dear MITgcm Support Team,<br>
> <br>
> 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.<br>
> <br>
> 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.<br>
> <br>
> I am considering whether surface current nudging (similar to SST/SSS) is possible or advisable. Specifically:<br>
> <br>
> Can pkg/ctrl be used to weakly/daily constrain surface currents or SSH?<br>
> Is there any recommended approach to improve surface currents without suppressing eddies?<br>
> Any guidance would be appreciated.<br>
> <br>
> Kind regards<br>
> <br>
> ```````````````````````````````````````````````<br>
> <br>
> Killampalli Rajesh (Research Scholar)<br>
> <br>
> Centre For Atmospheric Sciences,<br>
> <br>
> Indian Institute of Technology, Delhi<br>
> <br>
> Hauz Khas, New Delhi - 110016<br>
> <br>
> O-Email: <a href="mailto:asz238484@iitd.ac.in" target="_blank">asz238484@iitd.ac.in</a><br>
> <mailto:<a href="mailto:rajesh93.cstaff@iitd.ac.in" target="_blank">rajesh93.cstaff@iitd.ac.in</a>><br>
> P-Email: <a href="mailto:rajesh70530@gmail.com" target="_blank">rajesh70530@gmail.com</a> <mailto:<a href="mailto:rajesh93.cstaff@iitd.ac.in" target="_blank">rajesh93.cstaff@iitd.ac.in</a>><br>
> Phone: +91 9492068095.<br>
> <br>
> ```````````````````````````````````````````````<br>
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