[MITgcm-support] Interpolation issue: wet grid-pts with theta=0 identically

[Juncheng Zhang]

Hi Flynn,

You are right, thank you!
I found the ‘new wet grid-pts ‘ you mentioned and extrapolated the temperature and salinity, the error is solved.


Kind Regards
Juncheng Zhang
PhD Student,
Earth, Atmospheric, and Planetary Physics

Department of Physics
University of Toronto
McLennan Physical Laboratories
60 St Gorge St
Toronto, Ontario, M5S 1A7

juncheng.zhang at mail.utoronto.ca<mailto:juncheng.zhang at mail.utoronto.ca>

[Pursue STEM]<https://www.physics.utoronto.ca/>


From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Flynn Ames <f.ames at pgr.reading.ac.uk>
Date: Tuesday, 10 June 2025 at 04:09
To: mitgcm-support at mitgcm.org <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] Interpolation issue: wet grid-pts with theta=0 identically
You don't often get email from f.ames at pgr.reading.ac.uk. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification>
Hi Juncheng,


The error might be occurring because, as you increase resolution while maintaining the same bathymetry profile, you will resolve more of the detail of the bathymetry profile.
As a result, at the bottom boundary in the 1km simulation, you have 'new' wet grid points that were not present in the 5km simulation (i.e., vertical levels at some lat-long positions that were previously dry will now be wet).

My guess is that when you interpolate to 1km resolution, you aren't filling the 'new' wet grid points with any non-zero value values, which is why the model throws the error.
When ignoring the error, you are initialising the model with a temperature of zero degrees at 2981 grid points at the bottom boundary.
If you are you are providing other initial conditions (e.g., velocity fields), you will also likely be initialising these with values of zero. This could potentially be causing the numerical artifacts.

Admittedly I'm not sure what the best way round this. Perhaps creating a 'buffer layer' at the bottom of your interpolated fields (e.g., where you take the interpolated temperature field and create an extra layer of non-zero values at the ocean bottom, perhaps just copy-pasting the value of temperature from the grid cell above) could be something to try?


Cheers,
Flynn
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org> on behalf of Juncheng Zhang <juncheng.zhang at mail.utoronto.ca>
Sent: 09 June 2025 5:49 PM
To: MITgcm Support <mitgcm-support at mitgcm.org>
Subject: [MITgcm-support] Interpolation issue: wet grid-pts with theta=0 identically

You don't often get email from juncheng.zhang at mail.utoronto.ca. Learn why this is important<https://aka.ms/LearnAboutSenderIdentification>

Dear all,



I am using MITgcm to run a 1km high-resolution simulation based on the tutorial reentrant channel,

I first run a 5 km simulation, then use the output of 5km run as the initial condition of my 1km run,

However, after I  did the interpolation of 5 km output, and run the model, the error said below:



(PID.TID 0000.0001) *** ERROR ***  INI_THETA: found      2891 wet grid-pts with theta=0 identically.

(PID.TID 0000.0001) *** ERROR ***  If this is intentional, you need to set checkIniTemp=.FALSE. in "data", namelist PARM05



I know wet grid-pts relates to the parameter hFac? But I don’t know how to fix it,



And I tried to ignore this error by adding checkIniTemp=.FALSE., however, the simulation is not stable, and I had weird numerical artifacts appearing.



Thank you in advance, I appreciate any help.





Kind Regards

Juncheng Zhang
PhD Student,

Earth, Atmospheric, and Planetary Physics

Department of Physics
University of Toronto
McLennan Physical Laboratories
60 St Gorge St
Toronto, Ontario, M5S 1A7

juncheng.zhang at mail.utoronto.ca<mailto:juncheng.zhang at mail.utoronto.ca>

[Pursue STEM]<https://www.physics.utoronto.ca/>


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