[MITgcm-devel] negative snow thickness in thsice

[Jean-Michel Campin]

Hi Martin,

Thanks for reporting the problem. I don't have time to look at this
right now but will try in the coming weeks.

One thing that you may try would be to increase the minimun ice thickness
(e.g, 5 to 10 cm instead of the current default of 1.cm) to see if the problem 
goes away. It's safe to use a very small minimum ice-fraction but regarding the
minimum ice-thickness, not sure if too thin ice can trigger some Pb.

Cheers,
Jean-Michel

On Tue, Nov 24, 2015 at 06:31:14PM +0100, Martin Losch wrote:
> Hi Dimitris,
> 
> no, precipitation is never negative. I am using a CORE2 monthly climatology, the smallest value is 1e-12.
> 
> M.
> 
> > On 24 Nov 2015, at 18:18, Menemenlis, Dimitris (329C) <Dimitris.Menemenlis at jpl.nasa.gov> wrote:
> > 
> > A wild guess, probably not applicable to your case, but have you checked
> > surface forcing for negative precipitation?
> > 
> > I came across a similar problem recently with negative (SST cooling) swdown.
> > 
> >> On Nov 24, 2015, at 9:07 AM, Martin Losch <Martin.Losch at awi.de> wrote:
> >> 
> >> Dear thsice-users/developers,
> >> 
> >> I have come across a situation where I get slightly negative snow thickness (-0.0118 m), at the ice edge, where the ice cover fract = iceMaskMin (0.05), and iceH is also small (0.016 m). I cannot see anything extraordinary in any other variable. In the code I cannot find a place where this is caught (only iceH < iceMin), but with negative snow thickness the albedo computations are upset and the model stops (albedo < 0.2). 
> >> What are the circumstances under which snow thickness can become negative? I can only think of advection as the culprit (I use 77, so a flux limited scheme, pkg/seaice provides the ice drift velocities). If advection is to blame, it is probably safe to limit snow thickness to 0 for albedo computations. In fact when I do that, the model continues and the negative snow thickness disappears again. 
> >> 
> >> I am just a little worried that I am masking an underlying problem that could be fixed in a more consistent way. Are there any process other that advection that can cause negative snow thickness?
> >> 
> >> Martin
> >> 
> >> 
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