[CF-metadata] New standard_name values for some cloud and aerosol related variables

From: Jonathan Gregory <j.m.gregory>
Date: Wed, 30 Sep 2015 22:33:59 +0100

Dear Maarten

> ultraviolet_aerosol_index

> I've asked several specialists in the field to
> come up with a description of this parameter, and they warned: "Here
> is my attempt at defining a quantity that is far from clear". The
> description does cover what is in the parameter, and the name is
> easily found in literature.

OK. In that case I agree we can't make the name self-explanatory. If the
definition in the standard_name table could give an online literature ref
for how it is computed, that would help.

> >>Name: cloud_area_fraction_assuming_fixed_cloud_albedo
> >
> Yes, you do change the resulting cloud fraction if you assume a
> different cloud albedo. :-)
>
> It is frequently called an unhelpful 'effective cloud fraction'.
> many algorithms have taken a different approach, fix the cloud
> albedo to a fairly high value (0.8) and fit just two parameters:
> cloud_area_fraction_assuming_fixed_cloud_albedo and
> air_pressure_at_cloud_optical_centroid. Obviously if you assume a
> lower cloud albedo you will end up with a higher cloud fraction,
> most likely at a different pressure level.

Thanks for the explanation. I'm feeling uncomfortable about it because it's not
a real cloud area fraction, just an "effective" one to get the right answer.
By contrast, radiative fluxes assuming clear sky, for instance, are really the
output of radiative transfer calculations, with special conditions as input. I
agree that "effective" by itself is not informative, but we do use that word
in effective_radius for cloud particles, where it has the same purpose as in
your case. Would you mind including it here as well?
  effective_cloud_area_fraction_assuming_fixed_cloud_albedo
There is an existing standard name with "fixed" in it in this sense. If you
specify the value in a coordinate or scalar coordinate variable, I suggest
that it could have the existing standard_name of cloud_albedo, rather than
defining a new one.

> 1 is the only one we're interested in.

> There is a clear_sky label that is frequently used, but I haven't
> come across the opposite. What do you suggest?
> cloud_albedo_assuming_full_cloud_cover

Yes, that would make sense, I think, or it could be assuming_complete_cloud_
cover, or maybe assuming_completely_cloudy_sky, with is more like assuming_
clear_sky - what do you think? I expect that it will be useful in future to
have a phrase for this, which we currently lack, as you say.

Best wishes

Jonathan
Received on Wed Sep 30 2015 - 15:33:59 BST