[MITgcm-devel] conservation // sublimation

[Jean-Michel Campin]

Hi Martin and Gael,

I am not sure I am understanding every thing,
But I will still make few comments.

1) Martin: if would be usefull to know which CPP flags you turn on/off
in this legacy/evolution comparison on conservation.

2) I think it has been discussed previously (I don't remember when)
that sublimation is taken into account when computing (seace_solve4temp) 
tsurf and atmos-fluxes, but there is no snow/ice removal due to sublimation.
The diagnostic SIatmFW is consistent with this inconsistency
of seaice_growth (i.e, no eval over sea-ice covered region).
The diagnostic SIatmQnt seems right to me (easier to follow in the
evolution branch).
Is it right or has something changed in one of the branch (evolution/legacy)?

3) if point 2 is still valid, then the question remain: how to get
a meaningfull heat budget with a sublimation term which is present 
(for tsurf and heat fluxes) and missing (in FW) ?

4) I have the impression (when I read carefully the previous emails),
that the fact that there is no heat capacity in seaice, thus 
with surface atmos flux = conductive flux at seaice base (if tsurf < 0)
    or                  = excess of energy to melt (if tsurf = 0)
is the reason of some confusion. 
In fact, what is used, from seaice_solve4temp, in seaice_growth to 
grow or melt ice is the conductive-flux / excess of heat.
It just happens that it corresponds also to atmos surf flux, but it's 
just because we have a simple seaice model.
Does this make sense ?

Hope I am not increasing the confusion.

Cheers,
Jean-Michel

On Fri, Dec 10, 2010 at 10:43:51AM -0500, Gael Forget wrote:
> 
> > You can use the heat to either melt OR sublimate (melt+evaporate), but not for both. Either process can be done consistently. If you think that sublimation/(melting+evaporation) is faster than meltling+runoff into the ocean then you should use all hl=coeff*(qice-qsat) to sublimate (and saturate the atmosphere). If you melt and put the water into the ocean, you implicitly assume that there is no evaporation (maybe because the atmosphere is already saturated, or the water runs off more quickly). Both is possible, I am not sure what's more realistic, personally I feel it's the sublimation first, then melting.
> 
> Jean-Michel will know the correct answer... 
> 
> I still would think that the missing part is a fresh-water flux (ice -> water vapor) 
> that would imply a <0 latent heat storage on the atmosphere side (until it rains), 
> to compensate the >0 latent heat storage on the ocn/ice side. In analogy with evap.
> (I am not completely sure I got those signs correctly).
> 
> Cheers,
> Gael
>