[MITgcm-support] Bottom pressure, non hydrostatic run, in oceanic set up

[clement.soufflet at lmd.ens.fr]

Hi Martin,
Thank you for your answer. 
I tried to do calculate phiTotLow with this method but it produces incoherent results, I had positive pressure drag for instance witch in my case is impossible. 
So, I interpolated by hand phiHyd+phi_nh at the bottom and got more consistent result.
I don’t know if it is the better way to do it and I would be happy to hear if someone have another method using diagnostics already computed in the model.
Thanks again.
Clément

----- Mail original -----
De: "Martin Losch" <Martin.Losch at awi.de>
À: "mitgcm-support" <mitgcm-support at mitgcm.org>
Envoyé: Lundi 2 Décembre 2019 18:17:37
Objet: Re: [MITgcm-support] Bottom pressure, non hydrostatic run, in oceanic set up

Hi Clément,

this is clearly not an idiot question. I’ll try to answer with the hope that my answer will be corrected by someone who really knows:

The model carries the geopotential phi, and the total phi (hydro and non-hydrostatic) should be phiHyd+phi_nh at any depth level. As far as I can see, only the hydrostatic phi (phiHyd) is used to compute the diagnostics phiHydLow (in diags_phi_rlow.F). A good approximation to phiTotLow would be phiHydLow + phi_nh at the bottom-most “wet” level. Then you are still missing the contribution of phi_nh between the last center point and the actual bottom of the domain, but maybe that can be neglected if phi_nh is small?

phiHydLow needs to be scaled with rhoConst to be in pressure units. And then it’s only the part of the pressure that is not constant (i.e. the rhoConst*gravity*z is not part of this pressure).

Hope that helps,
Martin

> On 28. Nov 2019, at 13:25, <clement.soufflet at lmd.ens.fr> <clement.soufflet at lmd.ens.fr> wrote:
> 
> Hi,
> 
> I am running the MITgcm in non hydrostatic configuration, 2D, in oceanic set up, looking at pressure drag exerted on a topography.
> It could be an idiot question but I have some problem to get the surface pressure anomaly. In the netcdf output there are:
> phiHyd: the hydrostatic pressure
> phiHydLow: the hydrostatic pressure at the bottom
> phi_nh: the non hydrostatic pressure
> Is there a way to get the non hydrostatic pressure at the bottom?
> Or do I need to add the first level of the non hydrostatic pressure field to the hydrostatic pressure at the bottom to get it?
> ie:  P_bottom =  phiHydLow  + phi_nh(:,0)
> 
> Thanks,
> Clément
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> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support

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