Hi Richard,

I’m not sure about your proposed change to line 13421. As I understand it, if 
you do this then you will calculate the same absorption for oxygen regardless 
of what the user inputs for the O2 vmr. Is this desired behaviour? The MPM-type 
coefficients and equations in the Tretyakov 2005 paper assume a particular vmr 
(0.20946). Is it more correct to divide the calculated absorption by this 
value, and then multiply by the user-supplied vmr at the stage of the 
absorption calculation?

I also notice that the same VMRISO is in lots of the other complete O2 models 
(MPM87, MPM89 etc), so this isn’t restricted to Tretyakov-05


From: Richard Larsson <ric.lars...@gmail.com>
Sent: 22 October 2021 10:45
To: Fox, Stuart <stuart....@metoffice.gov.uk>
Cc: arts_dev.mi@lists.uni-hamburg.de
Subject: Re: Another Tretyakov-05 O2 absorption question

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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 value.

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 
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.



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