Numerical instabilities (spikes in the ice surface) at grounding line

Extension of Elmer in computational glaciology
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chenry
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Numerical instabilities (spikes in the ice surface) at grounding line

Post by chenry »

I'm running a simulation with a transient grounding line and am observing numerical instabilities in the form of spikes on the upper ice surface and inverted spikes on the lower ice surface. Has anyone else experienced this and has a solution to fix these numerical instabilities?
gagliar
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Re: Numerical instabilities (spikes in the ice surface) at grounding line

Post by gagliar »

Helo,

Can you be more specific? Are you running a Stokes or a SSA simulation? 2d or 3d? From which setup did you started?

Regards,
Olivier
chenry
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Re: Numerical instabilities (spikes in the ice surface) at grounding line

Post by chenry »

Hi Olivier,

Thanks for your reply. I am running a full Stokes 3D simulation and the grounding line in question is in a collision zone. The basal friction coefficient is set to 7.624e7 and the basal melt rate is dependent on the ice thickness and distance from the GL (Favier et al., 2016). Our current thinking is that the numerical instabilities could be caused by the resulting high melt rates in the collision zone. I have attached a couple of photos for reference.

Cheers,

Clara
UpperView.jpg
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LowerView.jpg
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gagliar
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Location: LGGE - Grenoble
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Re: Numerical instabilities (spikes in the ice surface) at grounding line

Post by gagliar »

Hi Clara,

Did you try to decrease your time step?

Also, having a water pressure dependent friction law might help by removing the discontinuity at the GL.

Hope it helps
Olivier
chenry
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Re: Numerical instabilities (spikes in the ice surface) at grounding line

Post by chenry »

Thank you for your help, Olivier. I was able to fix the problem in the end by avoiding a BMB discontinuity at the grounding line.

All the best,

Clara
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