[MITgcm-support] rStar with cavities

[Malte Jansen]

Hi Kaitlin,

I think that there is (or at least used to be) a potential problem with using rstar when you have thick sea ice - specifically when using rstar together with JMD95Z as the EOS. I don’t remember the details now,  but it has to do with spurious density gradients when rstar surfaces are tilted.  Setting selectP_inEOS_Zc=2 should fix the problem. I’ve had a long email conversation about this issue with Jean-Michel at some point. If you want, I can forward that to you.

Cheers,
Malte



On Oct 15, 2018, at 4:35 AM, Naughten, Kaitlin A. <kaight at bas.ac.uk<mailto:kaight at bas.ac.uk>> wrote:

Hi Martin,

Thanks for your response. Good to know that rStar should work with cavities. I suppose the differences between rStar and no-rStar could be that the "surf adjustment" the nonlinear free surface scheme is doing in the absence of rStar, i.e. adding water to the model in regions which violate hFacInf, is changing the tracer properties and/or circulation. I have a few patches of very thick sea ice which are depressing the sea surface and causing those hFacInf errors. So maybe rStar is actually more accurate than nonlinear free surface without rStar. I am trying a run now with the linear free surface for comparison.

Many thanks,
Kaitlin
________________________________
From: MITgcm-support <mitgcm-support-bounces at mitgcm.org<mailto:mitgcm-support-bounces at mitgcm.org>> on behalf of Martin Losch <Martin.Losch at awi.de<mailto:Martin.Losch at awi.de>>
Sent: 12 October 2018 16:15:24
To: MITgcm Support
Subject: Re: [MITgcm-support] rStar with cavities

Hi Kaitlin,

I think they should work together.
I have once (in the very beginning of this in 2006 or so) tried to use the rStar coordinates as surface (topography) following coordinates for better near surface resolution in the cavities, but because we don’t have a decent formulation for the pressure gradient for the case of strongly sloping vertical layer interfaces, this leads to too much pressure gradient error.

Martin


> On 10. Oct 2018, at 12:54, Naughten, Kaitlin A. <kaight at bas.ac.uk<mailto:kaight at bas.ac.uk>> wrote:
>
> Hi everyone,
>
> Is it okay to use rStar with the SHELFICE package? Looking at some old messages I can't figure out whether or not there is a problem with this. I ran with and without rStar and can see some non-negligible differences in the cavity, which is a bit concerning. Is it confirmed whether or not they work together?
>
> Many thanks,
> Kaitlin
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