Dear Mark
I can't remember whether I found any existing inconsistency. Are there any
names among those which were previously added for CFMIP that have the same
definitions of evaporation and condensation as you used? Thank you for
modifying your definitions and removing problems so that for the moment we
will not be introducing an inconsistency. Using the wider definitions of
evaporation and condensation means that it's simpler to name and discuss
phase transitions gas <-> liquid or solid, while sublimation and deposition
refer to gas <-> solid, but as you imply, we would need to find other words or
phrases to refer to gas <-> liquid. In support of the general definition,
I would note that vapour means gas, and condensed means not gas (as in
https://en.wikipedia.org/wiki/Condensed_matter_physics), so these words are
quite logical - but I would definitely not argue that languages are or should
be always logical! For CF consistency is a very important principle. We could
adopt your preferred definitions, if we renamed quite a few of the existing
standard names.
Best wishes
Jonathan
----- Forwarded message from Mark Webb <mark.webb at metoffice.gov.uk> -----
> Date: Wed, 15 Jul 2015 18:36:55 +0100
> From: Mark Webb <mark.webb at metoffice.gov.uk>
> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
> CC: Mark Webb <mark.webb at metoffice.gov.uk>, cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] proposal for new standard names for some cloud
> quantities
> User-Agent: Mutt/1.5.20 (2009-12-10)
>
> Dear Jonathan,
>
> Thanks for your comments.
>
> > Thanks very much. Having the definitions detail the processes helps a lot.
> > I do have a remaining concern about terminology, though, which probably should
> > have been noticed earlier. In the guidelines, "condensed water" means liquid
> > or solid (ice), for instance in mass_fraction_of_cloud_condensed_water_in_air,
> > which says this explicitly in its definition.
>
> > For consistency, "condensation" should mean gas -> liquid or solid. The
> > A Met Soc glossary says "in general" that's what condensation means, but
> > in meteorology it means gas -> liquid.
> > http://glossary.ametsoc.org/wiki/Condensation
> > It's unfortunate that it's ambiguous! I think the general definition is
> > more satisfactory.
>
> > The same entry says "evaporation" means liquid or solid -> gas i.e. the reverse
> > of condensation. That is the sense in which we use it in some other standard
> > names e.g. water_evaporation_flux. However the AMS entry for evaporation gives
> > this as its first sense, but remarks that it's "usually" liquid->gas. Again, an
> > unsatisfactory ambiguity, and I would prefer the broader definition. With the
> > broader definitions, deposition (gas -> solid) is a subset of condensation,
> > and sublimation (solid -> gas) a subset of evaporation.
> >
> > It looks like we may have some existing inconsistency between the meanings of
> > condensation and perhaps evaporation in standard names. Do you agree? If so we
> > should try to sort it out. An advantage of the broader definitions is you would
> > not have to say condensation_and_deposition, since it's all condensation.
>
> I've given this quite a bit of thought and I'm afraid that I'm unsure
> about the best way to proceed. Personally I prefer the definition
> in common usage in meterology which restricts condensation and
> evaporation to vapour/liquid transitions and uses deposition/
> sublimation as well. I see this as more precise because it allows
> for the future possibility of supporting variables which separate
> condensation and deposition for example. But I also very much take
> your point that this is potentially inconsistent with other terms
> already defined in the standard names such as water_evaporation_flux
> /condensed_water. (I think that the current standard names are
> consistent in this sense - but I may have missed something. Was
> there a particular inconsistency that you had spotted?)
>
> For the moment I have modified my proposal to remove references
> to condensation/evaporation - hopefully the definitions below
> are now unambigous. This has required removing a couple of
> variables. I will think about the best way to propose these
> at a future date. I'll have to decide whether to adopt
> your suggestion or whether to propose more wide ranging changes
> to the standard names to make them consistent with my preferred
> definition for condensation/evaporation.
>
> Here is my updated proposal. Please let me know if you have any
> concerns with it is it now stands.
>
> Thanks!
> Mark
Received on Fri Jul 17 2015 - 07:49:41 BST
