[MITgcm-support] [EXTERNAL] Treatment of Antarctic grounding zone regions

[Pochini, Enrico]

Hi Paul,

Thank you very much for the information!
I'm using a static ice shelf, so I think I will continue applying the
digging method.

Kind regards,

Enrico



Il giorno mer 18 nov 2020 alle ore 20:33 Paul Holland - UKRI BAS <
pahol at bas.ac.uk> ha scritto:

> Hi Enrico
>
> Briefly, I always choose to 'dig' out the cavity in order to make sure
> that all of the floating ice has some ocean under it.  My logic is that we
> know the grounding line very well from satellite interferometry, but we do
> not know the seabed/ice bed very well at all, and so I always choose to
> sacrifice the seabed in order to preserve the grounding line.
>
> When doing the 'digging', we usually choose to do it in such a way that
> the velocity points on the C grid have two cells open in the vertical.
> This would in theory make sure that all ocean columns can be connected to
> each other with a very under-resolved overturning circulation.  This gets a
> bit complicated with partial cells.  You can see in Kaitlin Naughten's
> github code you refer to exactly how she is handling this.  Basically, you
> have to over-dig the tracer point bathymetry in order to make sure that the
> velocity points are open, however you want them to be.
>
> The above logic of digging the seabed only applies to simulations with
> static ice.  If you had a coupled ice sheet model, it would be a bit
> strange to dig the seabed in different places as the model advances or
> retreats the ice.  In that case, we have adopted other strategies,
> including digging the ice instead of the seabed (i.e. shallowing the ice in
> order to preserve a modellable water column thickness) and other trickery
> with the streamice package.
>
> I hope that helps a bit...
>
> Cheers
>
> Paul
>
> -------------------
> Message: 2
> Date: Wed, 18 Nov 2020 06:55:51 -0800
> From: Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
> To: MITgcm Support <mitgcm-support at mitgcm.org>, Yoshihiro Nakayama
> <Yoshihiro.Nakayama at lowtem.hokudai.ac.jp>, "Michael P. Schodlok"
> <Michael.P.Schodlok at jpl.nasa.gov>
> Subject: Re: [MITgcm-support] [EXTERNAL] Treatment of Antarctic
> grounding zone regions
> Message-ID: <C8C7DE4E-7A33-48F0-8803-32F35C681DBF at jpl.nasa.gov>
> Content-Type: text/plain; charset="us-ascii"
>
> Michael and Yoshi, do you have any advice to give for question below?
> What decision did you make for your hi-res simulations, e.g., for:
> https://www.nature.com/articles/s41598-019-53190-6
>
> Thanks, Dimitris
>
> > On Nov 18, 2020, at 6:47 AM, Pochini, Enrico <epochini at inogs.it> wrote:
> >
> > Dear community,
> >
> > I have a question for the polar oceanographers:
> >
> > I have noticed that in bathymetric reconstructions available for
> Antarctica (e.g. Bedmap2, RTopo-2) there are regions corresponding to the
> grounding zone of the biggest ice shelves where the water column thickness
> (resulting from the subtraction draft - bathy) equates exactly 1m.
> >
> > For my simulations I work in the Ross Sea at 5km resolution and vertical
> layers of a few tens of metres at the depth of the grounding zone. I am
> wondering whether this region should be cut out directly as non-resolvable
> in my vertical discretization, or whether, in a less conservative approach,
> the bathymetry should be deepened in order to resolve the region in at
> least one layer.
> >
> > Employing a preprocessing algorithm (
> https://github.com/knaughten/mitgcm_python <
> https://urldefense.us/v3/__https://github.com/knaughten/mitgcm_python__;!!PvBDto6Hs4WbVuu7!bWCWtDMcJoVTIrR5IAjyeN1eGS1eXJVRuH3eFS2l_JFJ3IhWUV5BBvLC7nnfv5WjG2XalrUIZ7A$>)
> I obtain a grounding-zone water-thickness of ~ 50-80 m, enough to fit ~1-2
> layers.
> >
> > I am uncertain about which way to take, so I'm curious to hear how you
> treat such thin cavities in high resolution models in other Antarctic seas,
> whether you cut them or keep them, and how you make them resolvable without
> affecting too much the overall setup.
> >
> > Thanks!
> >
> > Enrico P.
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