Hi Patrick, Hi all,

On Fri, Apr 5, 2019 at 6:16 AM Patrick Eriksson <
patrick.eriks...@chalmers.se> wrote:

> Are you just interested in the Jacobian or will you also perform
> retrievals (by Qpack?)?

for now, just in the Jacobians.

though, the setup for the O3 Jacobians as we used so far comes from Uwe's
O3 retrieval processing. I start thinking that the logrel setting is
probably not the best when trying to understand the meaning and the role of
Jacobians, and when comparing the O3 Jacobians, e.g. to the wind Jacobians
(@Mathias, @Rita, we should probably discuss this...).

later this shall result in retrievals (of wind, actually), likely using
qpack (for the simple reason that we use Uwe's O3 retrieval as
example/proxy/base and this is using qpack).

> > our main issue here is to understand what unit logrel(O3) implies.
> > following Patrick's advice from the previous (wind) thread, I checked
> > the AUG (and the correct one for that matter - cause we're still using
> > arts2.2; 'logrel' retrieval unit seems to be gone in arts2.3) - et voila!
> > (it's sec. 16.4 for all others interested in the matter)
>  >
> > so, according to my understanding of Sec16.4, 'logrel' is (at least
> > regarding the Jacobian output) identical to 'rel', which in turn for the
> > (semi-)analytical jacobians corresponds (or, is scaled) to a 100% change
> > in the abs species (here, O3) with respect to the species' VMRs (as
> > given by the vmr_field interpolated to the species' Jacobian p_grid). Is
> > that understanding correct?
> I would say yes. In my words: If we denote "logrel" as z, then
> z=log(x/xa). That is you retrieve the log of ratio with respect to a
> priori.
> logrel and rel give identical results for the first iteration of a
> retrieval. But differ for later iterations (handled by Qpack).

so, logrel and rel only make a difference in a (externally coupled)
retrieval, e.g. with qpack, not with plain ARTS. is that correct?

so, when I'd like to label a (logrel) O3 Jacobians plot, I could use K /
100% O3? or what would you suggest?
(well, just for this sake it's probably more straight-forward to use 'vmr'
units and label them K/1 or rescale them to K/ppm...)

> > and how is that for 'vmr' then? would the jacobians correspond to a '1'
> > (or 10^6 ppm) change in the species? or a 1ppm change? (i'm unsure what
> > VMR's SI unit is...).
> All Jacobians are for a unit change, so here it is "1!. That is, what
> change would you get if you add a full atmosphere of the gas of concern.

Ok, thanks for the confirmation!

Best wishes,

Jana Mendrok, Ph.D. (Geoscience)

Email: jana.mend...@gmail.com
Phone : +46 (0)708 860 729
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