Hi Stuart,

I think you have found a bug.  The isotopologue ratio is not fixed
anywhere, yet the VMRISO variable has been scaled down by its assumed
value.  The comment for this value is simply false today, it must have
changed sometime without anyone noticing.

I think that VMRISO should be changed to simply be equal to the input vmr

The particular line for the VMRISO number today is
legacy_continua.cc::13327.  If that line is commented out and instead line
legacy_continua.cc::13421 is rewritten as "(...) / vmr[i]", I think you
will get better results.

Could you check if this change improves your results?

With hope,

Den mån 18 okt. 2021 kl 12:28 skrev Fox, Stuart <stuart....@metoffice.gov.uk

> Hi ARTS devs,
> I’ve got another question about the Tretyakov-05 complete absorption
> implementation in ARTS. In the code for TRE05O2AbsModel, the line
> absorption is calculated, and then converted in the final line into a
> partial cross-section. When calculating this cross-section a constant equal
> to the O2 vmr assumed by Tretyakov 2005 (0.20946) multiplied by the main
> isotope abundance is used, rather than just the O2 vmr. Should the isotope
> abundance really be included here? Presumably it depends on whether it is
> also included at the stage of the absorption calculation, or if the total
> O2 vmr is used there, but I’m not familiar enough with the ARTS code to
> know which is the case? I guess I would expect it should work properly for
> the case where the user defines “abs_species_O2” without explicitly setting
> an isotopologue ratio; the tests I’ve done suggest this is not currently
> the case.
> Regards,
> Stuart

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