[MITgcm-support] instability with shelf ice package

[Dustin Carroll]

Hi Liu,

This sounds like a problem with your shelfice load anomaly. How are you calculating your load anomaly file (the pressure load anomaly at the bottom of your ice shelf)? This can be an issue, especially If you have complex topography under your ice shelf. If your pload doesn’t lead to a balanced initial state, you will have large adjustments of the free surface leading to CLF violations.

As a test, turn off the turbulent transfer coefficients (set gamma_T/S = 0 in data.shelfice). If your model is still blowing up immediately it’s probably your initial conditions. Look at advcfl_uvel, advcfl_vvel, and advcfl_wvel, in your STDOUT file and see if they go to >1 and then return nan's right away.

Another way to debug this problem is to set your dumpfreq to the first few time steps. If you see spurious mixing and instabilities right away (especially near topography) thats a good clue the model isn’t adjusting well to the pressure anomaly created by your ice shelf.

KPP works with the shelfice pkg but underneath the ice shelf it only uses the internal instability part of the scheme (based on the Richardson flux number). This is similar to "implicit diffusion” — you are losing all the extra features of KPP. You can try a simple convective adjustment scheme (cAdjFreq = -1) while testing.

Cheers,
Dustin



> 
> Dear all:
>  
>      I am still trying to set up a regional experiment with OBCS in the Prydz Bay. In order to get a proper simulation in this Antarctic region, I set up this
> experiment with obcs package, seaice package, shelf ice package. When I start to run this model, it blows up very soon. Then, I start to check which package
> should be Responsible for this. When I turn off the shelf ice package, by deleting useSHELFICE = .TRUE. in the data.pkg, the model runs very well. So, I
> believe that the setting for the shelfice package should be something wrong in my simulation.
> 
>      To search some possible clues, I went to the description of the shelf ice package in the manual again. In 6.6.3.2, it says “If you use it together with vertical
> mixing schemes, be aware, that non-local parameterizations have been turned off, e.g. for KPP”. Does it mean, when I want to use shelfice, I have to stop use
> KPP, i.e., when I set useSHELFICE = .TRUE. in the data.pkg, I have to delete useKPP = .TRUE. If I have to delete useKPP = .TRUE. in the data.pkg, what else
> vertical mixing scheme could be used in my case.
>  
> 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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>  
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