Hej igen,

> Yes, this puts some weight on the user. Hydrostatic equilibrium (HSE) is a 
> similar case. Input profiles do not always fulfil HSE (this is the case for 
> Fascod, if not a mater of geopotential vs geometric altitudes?).

Could this for Fascod also be due to the VMR definition, perhaps?

> For HSE it is up to the user to apply this "fine tuning" or not. This 
> including to include adding call of the HSE method in OEM iterations, to make 
> sure that HSE is maintained after an iteration. The VMR rescaling should also 
> be included in the iteration agenda, if the retrieval can change H2O close to 
> the ground. That is, a VMR rescaling would not be something completely new, 
> as I see it.

It seems to me that this leads into a logical loop: If you retrieve H2O and O3, 
and the retrieved H2O value directly affects the O3 value due to the rescaling. 
As you write, in principle, this should even be in the Jacobian, as a 
cross-term. With more water, the lines of all other gases get weaker.

It is true that if there is more of the one there has to be less of the other, 
but argh, this is so ugly.

Perhaps the deeper reason why AER went for the other definition? If VMRs refer 
to the dry pressure, and the dry gases are all either quite constant or very 
rare, then retrievals are more independent.


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