[MITgcm-support] Calculation of the value of the density in the SHELFICEloadAnomal yFile in data.shelfice

Martin Losch Martin.Losch at awi.de
Sat Oct 11 18:50:01 EDT 2014

Hi Liu,

The principle behind this is: When you “put in” an ice shelf it replaces the ocean water and by Archmedes’ principle it’s total mass is the same as that of the water it replaces. You cannot know rho* exactly except for idealized experiments, but you have to find some approximation to it so that your Ptop is in approximate balance with your surrounding hydrography. rho* can be something like the average of the surrounding ocean densities extrapolated into the ice shelf. 
When you start the model, the free surface will adjust to your Ptop; if you have chosen a Ptop (rho*) that is far from equilibrium, then the adjustmet will be large, leading to large velocities and then to numerical instability. You then either improve your Ptop (preferred and usually not difficult), or you run the model with very short time step for a spinup that can handle the large adjustments until there is a quasi-equilibrium (with some funny free surface ETAN in the ice cavities).

Hope that helps,


On Oct 11, 2014, at 8:53 PM, 刘成彦 <killy at nuist.edu.cn> wrote:

> Dear all,
> I still have some problem in my experiment on the Amery Ice shelf. In my former emails, I have discussed it with Dustin, and he suggestions did help me to
> realized that I need put my attention to the ‘SHELFICEloadAnomalyFile’ in the data.shelfice. After read the manual, it suggests that this file supplys the
> pressure load anomaly at the bottom of the ice shelves. Its value is Ptop-g*Σρ0*delz, and the Ptop is defined as Ptop=Pa+ g*Σρ**delz.
> These rho makes me confuse…..
> The first one,ρ0, denotes the rhoConst in manual, and I have find it in the STDOUT.0000 file, with a value of 1027.5 kg/m3.
> The second one, ρ*, is defined as ‘constant in time and corresponds to the sea-water replaced by ice’.
> So I can not figure out what is the meaning of the second one, and how can I get the value of this density?
> Dose it means the density of the ice shelf, or something else?
> I have read the section SHELFICE configuration, compiling & running in the manual, and the paper “Modeling ice shelf cavities in a z coordinate ocean
> general circulation model”, but I still cannot get clear with the second density.
> Thank you for your considerations!
> Cheers
> Liu
> ----------------
> *********************************************
> Dr. Chengyan Liu
> Nanjing University of Information
> Science & Technology
> No.219, Ningliu Road, Nanjing, Jiangsu,
> China(Postcode: 210044)
> Phone: 18251854735
> E-Mail: killy at nuist.edu.cn
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