[MITgcm-devel] seaice_solve4temp.F cleaning update

[Jean-Michel Campin]

Hi Ian,

On Thu, Feb 02, 2012 at 04:33:05PM -0800, Ian Fenty wrote:
> J-M,
> 
> > Sea-Ice physics:
> > I think we should add the conductive heat flux as output argument of S/R solve4temp
> > so that when the surface is melting (e.g., melting snow), we keep the 
> > conductive heat flux Fc = effCond*(Tbase - Tsurf) = effCond*(-1.9 - 0)
> > to melt the bottom of the ice (and not the snow as it is now)
> 
> Can you please clarify this idea for me?  
I will try.

> When (Tbase - Tsurf) < 0 then the direction of the heat conduction is from the ice (or snow) surface down into the ice.  Why not melt from the top down?  What is the advantage of partitioning this component of the surface heat flux convergence to melt at the base?  
I am more familiar with non-zero heat capacity seaice (this was my "Sea-Ice physics"
section), and in this case, it's clear that the distinction has to be made.
But even with zero heat capacity, the vertical profile of temp in snow+ice
will be monotonous, the surface is @ tmelt=0.degC, the bottom is @ seawater-Tfreeze
= -1.9 in this simple case, so anywhere in the snow layer t < tmelt=0 except @ the 
surface where t=tmelt, so that no interior snow melting. And the surface snow melting
should be just proportinal to the heat convergence at the surface, i.e. F_c - F_ia 
(convention: +=up) (and not just -F_ia as it is now), 
and the conductive heat flux F_c < 0 should be used to melt seaice at the bottom
according to the heat flux convergence @ the bottom: F_ocean - F_c 
with F_ocean(+=up) = ocean turbulent heat flux @ the ice-ocean interface,

> I'm afraid I don't see the answer in the Nov 2010 discussion.
The reference to the "Nov 2010 discussion" was meant to be understood
in the context of "If we follow this route", i.e., if we make this
distinction between F_ia and F_c, which I re-stated just after:
"but it only makes a difference if we export Fc to seaice_growth".
But, the big problem is that the link I sent was not the good one !
Sorry for that. The response I wanted to point to was from the day after, 
Dec 01, 2010, same discussion, same subject:  
http://mitgcm.org/pipermail/mitgcm-devel/2010-December/004410.html
Hope it's more clear now.

Cheers,
Jean-Michel

> > If we follow this route, then it makes sense, after the tsurf iteration, 
> 
> -Ian
> 
> 
> > And use the surface heat flux convergence = Fc - F_ia to do surface melting.
> > 
> > If we follow this route, then it makes sense, after the tsurf iteration, 
> > to update the atmospheric heat flux F_ia using the linearized approximation
> > in order to conserve and to keep exactly Fc = F_ia when no surface melting.
> > I tried to make this point a year ago, in this discussion:
> > http://mitgcm.org/pipermail/mitgcm-devel/2010-November/004408.html
> > but it only makes a difference if we export Fc to seaice_growth.
> > 
> > I am going to add this option (to update F_ia using linearized approximation)
> > in case one day we want to improve seaice_growth.
> > 
> > Cheers,
> > Jean-Michel
> > 
> > _______________________________________________
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> > MITgcm-devel at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-devel
> 
> 
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