[MITgcm-devel] negative H in calc_r_star.F

[Jean-Michel Campin]

Hi Dimitris,

I will take a look at the r-star code to check pkg/shelfice issue.

Just to clarify: you don't have negative H with linear free-surf,
only when you try to use r-star, right ? or did I missed something ?

And OBCS does work with r-start, see verification/exp4/input.nlfs/

Cheers,
Jean-Michel

On Tue, May 29, 2012 at 03:47:48PM +0000, Menemenlis, Dimitris (3248) wrote:
> Jean-Michel, could you advise on r-star and shelfice.  We'd really like to be able to use both together, if possible.
> 
> Martin, I am guessing that your simple experiments may not have worked because you were using open
> boundaries, and I think that r-star and obcs do not yet work together.  The CS510 configuration is global.
> 
> Another possibility is that you had negative H's in your configuration.
> The negative H comes from computing the thickness of the wet cell wall between two adjacent grid boxes.
> It is computed as: MIN( Ro_surf(i-1,j), Ro_surf(i,j) ) - MAX( R_low(i-1,j), R_low(i,j) )
> There is no check to see whether the above gives a negative number, so if your bathymetry and ice shelf
> topography has a slope such that it generates negative H's, the code will stop.
> 
> By coincidence, in the original (cube86) configuration we did not generate negative H's so the code run OK.
> When we switched from hFacMinDr=50 to hFacMinDr=0, however, we started causing a bunch of negative H's.
> 
> Those are guesses.  Let's wait to hear from Jean-Michel about this.
> 
> Thanks
> 
> Dimitris Menemenlis
> 
> On May 29, 2012, at 2:11 AM, Martin Losch wrote:
> 
> > I think you can still use this code if it works. I just could never make it work for my simple experiments. And you Eta looks OK to me (Eta is not the issue anyway). I don't know anything about the negative H.
> > 
> > Martin
> > 
> > On May 25, 2012, at 9:12 PM, Menemenlis, Dimitris (3248) wrote:
> > 
> >> Ooops!
> >> 
> >> This means that for past three years we have boldly been going where we had no business of going :-(
> >> 
> >> http://ecco2.jpl.nasa.gov/data1/cube/cube86/input/ETANjan08.jpg
> >> is a figure of ETAN on the Antarctic face of the cube86 global CS510 configuration after 16 years of integration.
> >> 
> >> Apart from fact that one can end up with negative H at edges of grid cells, which was not the case for cube86,
> >> what other aspects of the existing "r_star + shelfice"  solutions are likely to be problematic?
> >> 
> >> Shall we add a stop or a warning to shelfice_check.F when r_star is enabled?
> >> 
> >> Dimitris Menemenlis
> >> 
> >> On May 25, 2012, at 12:52 AM, Martin Losch wrote:
> >> 
> >>> I am not aware, that shelfice can be used with r-star! 
> >>> 
> >>> M.
> >>> 
> >>> On May 24, 2012, at 9:30 PM, Dimitris Menemenlis wrote:
> >>> 
> >>>> Jean-Michel and Martin, is it allowable to have negative H in calc_r_star.F  when using pkg/shelfice ?
> >>>> 
> >>>> When we went from hFacMinDr=50 to hFacMinDr=0 in order to better represent the ice shelf cavity,
> >>>> we end up with following situation:
> >>>> 
> >>>> WARNING: r*FacW < hFacInf at       1 pts : bi,bj,Thid,Iter=   1   1   1        10
> >>>> e.g. at i,j=   9  99 ; rStarFac,H,eta =  0.019415 -1.499939E-01  1.689013E-01  1.252815E-01
> >>>> STOP in CALC_R_STAR : too SMALL rStarFacW !
> >>>> 
> >>>> I am pretty sure that H is non-zero in center of cell - Hong is double checking.
> >>>> ... but shouldn't H at the edges of the cells be set to zero when
> >>>> MIN( Ro_surf(i-1,j), Ro_surf(i,j) ) - MAX( R_low(i-1,j), R_low(i,j) )
> >>>> is negative?
> 
> 
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