Dear Heinke, Christiane, Jonathan and Luca,
Please see below for my comments on the various optical_thickness names,
some of which raise important questions regarding their definitions.
optical_thickness and absorption_optical_thickness
**************************************************
atmosphere_optical_thickness_due_to_ambient_aerosol; 1
The standard name table already contains the name
atmosphere_optical_thickness_due_to_aerosol. Under the thread
'Modification of some existing CF standard names for chemical
constituents' it was agreed that any older aerosol names (which existed
prior to the introduction of the dry/ambient aerosol distinction) should
be aliased to 'ambient_aerosol' names. Therefore, the name would become
atmosphere_optical_thickness_due_to_ambient_aerosol as proposed. So
far, so good. However, complications arise when considering the
definition of this name.
Currently, the definition of atmosphere_optical_thickness_due_to_aerosol
reads as follows:
'The specification of a physical process by the phrase due_to_process
means that the quantity named is a single term in a sum of terms which
together compose the general quantity named by omitting the phrase. The
optical thickness is the integral along the path of radiation of a
volume scattering/absorption/attenuation coefficient. The radiative flux
is reduced by a factor exp(-optical_thickness) on traversing the path.
The atmosphere optical thickness applies to radiation passing through
the entire atmosphere. "Aerosol" means the suspended liquid or solid
particles in air (except cloud droplets).'
The addition of 'ambient' to the name would lead to the following two
sentences being added to the end of the definition:
'"Ambient aerosol" is aerosol that has taken up ambient water through
hygroscopic growth. The extent of hygroscopic growth depends on the
relative humidity and the composition of the aerosol.'
This is fine and doesn't pose any problems.
I think the difficulty arises in the definition of 'optical_thickness',
specifically the sentence 'The optical thickness is the integral along
the path of radiation of a volume scattering/absorption/attenuation
coefficient.' This seems to imply that integration of any of the
coefficients can be called simply optical_thickness, i.e. it is a
generic term for both 'total' optical thickness and any of its
components. However, in this thread we now have proposals for separate
absorption_optical_thickness and optical_thickness names, where
optical_thickness is the sum of scattering and absorption (and allows
for the introduction of scattering_optical_thickness names if needed in
future). Furthermore, Christiane has suggested adding a sentence to the
definition of optical_thickness saying something like "Optical thickness
is the sum of scattering and absorption components." The problem is
that this proposed addition, while making perfect sense on its own,
seems to conflict with the existing definition. I think that simply
adding the new sentence will create a definition that contradicts
itself, which isn't acceptable. However, if we delete the words
'scattering' and 'absorption' from the existing sentence so that it
reads 'The optical thickness is the integral along the path of radiation
of a volume attenuation coefficient' we are effectively changing the
meaning of the name which will affect any existing data that use it, and
that also wouldn't be acceptable! It's not clear to me how to resolve
this question over the definition and I'd welcome any thoughts on the
matter.
atmosphere_optical_thickness_due_to_sulfate_ambient_aerosol; 1
The name is fine but the question about the 'optical_thickness'
definition also applies to this name.
atmosphere_absorption_optical_thickness_due_to_ambient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_dust_ambient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_particulate_organic_matte
r_ambient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_sulfate_ambient_aerosol;
1
atmosphere_absorption_optical_thickness_due_to_seasalt_ambient_aerosol;
1
atmosphere_absorption_optical_thickness_due_to_black_carbon_ambient_aero
sol; 1
These names are all accepted - I think new, more specific, names can be
introduced regardless of how we decide to treat the 'total' optical
thickness definitions.
atmosphere_absorption_optical_thickness_due_to_water_ambient_aerosol; 1
I note the earlier conversation about the use of '_in_', which resulted
in it being deleted from all these names. However, I think it shouldn't
have been deleted from this last one, so it should read:
atmosphere_absorption_optical_thickness_due_to_water_in_ambient_aerosol
like the existing name
atmosphere_optical_thickness_due_to_water_in_ambient_aerosol. Does
everyone agree?
optical_thickness and absorption_optical_thickness(mode)
********************************************************
Heinke, in her 16 December 2008 posting gives the following possible
alternatives for these names:
atmosphere_absorption_optical_thickness_due_to_accumulation_mode_ambient
_aerosol; 1
or
atmosphere_absorption_optical_thickness_due_to_accumulation_soluble_mode
_ambient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_accumulation_mode_dry_aer
osol; 1
or
atmosphere_absorption_optical_thickness_due_to_accumulation_insoluble_mo
de_ambient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_coarse_mode_ambient_aeros
ol; 1
or
atmosphere_absorption_optical_thickness_due_to_coarse_soluble_mode_ambie
nt_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_coarse_mode_dry_aerosol;
1
or
atmosphere_absorption_optical_thickness_due_to_coarse_insoluble_mode_amb
ient_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_aitken_mode_ambient_aeros
ol; 1
or
atmosphere_absorption_optical_thickness_due_to_aitken_soluble_mode_ambie
nt_aerosol; 1
atmosphere_absorption_optical_thickness_due_to_aitken_mode_dry_aerosol;
1
or
atmosphere_absorption_optical_thickness_due_to_aitken_insoluble_mode_amb
ient_aerosol; 1
atmosphere_optical_thickness_due_to_accumulation_mode_ambient_aerosol; 1
or
atmosphere_optical_thickness_due_to_accumulation_soluble_mode_ambient_ae
rosol; 1
atmosphere_optical_thickness_due_to_accumulation_mode_dry_aerosol; 1
or
atmosphere_optical_thickness_due_to_accumulation_insoluble_mode_ambient_
aerosol; 1
atmosphere_optical_thickness_due_to_coarse_mode_ambient_aerosol; 1
or
atmosphere_optical_thickness_due_to_coarse_soluble_mode_ambient_aerosol;
1
atmosphere_optical_thickness_due_to_coarse_mode_dry_aerosol; 1
or
atmosphere_optical_thickness_due_to_coarse_insoluble_mode_ambient_aeroso
l; 1
atmosphere_optical_thickness_due_to_aitken_mode_ambient_aerosol; 1
or
atmosphere_optical_thickness_due_to_aitken_soluble_mode_ambient_aerosol;
1
atmosphere_optical_thickness_due_to_aitken_mode_dry_aerosol; 1
or
atmosphere_optical_thickness_due_to_aitken_insoluble_mode_ambient_aeroso
l; 1
There are three issues regarding these names and their definitions:
1) The question of whether to use
a) dry_aerosol or insoluble_mode_ambient_aerosol
b) ambient_aerosol or soluble_mode_ambient_aerosol
Luca (2 December 2008) wrote:
>
> The definition "accumulation_mode_ambient_aerosol" and
"accumulation_mode_ambient_aerosol" may be confusing, as one could
understand the difference
> between these two variables is just the presence of water on the same
distribution of particles. But in fact I would like two describe two
> different. particle distributions, both are at ambient conditions but
one is composed of particles which can uptake water (soluble particles),
and
> another one which cannot uptake water in ambitn conditions (insoluble
particles). So one possibility for the variables above is:
>
atmosphere_optical_thickness_due_to_accumulation_soluble_mode_ambient_ae
rosol
>
atmosphere_optical_thickness_due_to_accumulation_insoluble_mode_ambient_
aerosol'
>
>From this I understand that 'insoluble' aerosol must always be dry
because it cannot take up water. I am not clear, however, whether the
'soluble' aerosol has indeed taken up water because it is in ambient
conditions, or simply that it is capable of doing so. I assume the
former, but it would be helpful if someone could confirm that.
Currently standard names definitions describe 'dry_aerosol' as follows:
' "Aerosol" means the suspended liquid or solid particles in air (except
cloud droplets). Aerosol takes up ambient water (a process known as
hygroscopic growth) depending on the relative humidity and the
composition of the aerosol. "Dry aerosol" means aerosol without water.'
The description of 'ambient_aerosol' is ' "Aerosol" means the suspended
liquid or solid particles in air (except cloud droplets). "Ambient
aerosol" is aerosol that has taken up ambient water through hygroscopic
growth. The extent of hygroscopic growth depends on the relative
humidity and the composition of the aerosol.'
The current descriptions say nothing about whether a particular dry
aerosol species is actually capable of taking up water. However, Luca
needs to make this distinction. Perhaps we could do this by introducing
the terms 'dry_insoluble_aerosol' and 'dry_soluble_aerosol' instead of
simply 'dry_aerosol' in cases where the distinction is important. I
assume that, by definition, ambient aerosol is soluble so I think we
could probably just stick to calling it 'ambient_aerosol'. If we were
to follow this suggestion we would introduce names such as:
atmosphere_optical_thickness_due_to_accumulation_mode_ambient_aerosol
(instead of soluble_mode_ambient_aerosol)
atmosphere_optical_thickness_due_to_accumulation_mode_dry_insoluble_aero
sol (instead of insoluble_mode_ambient_aerosol).
I think this syntax is also better because it reunites the word 'mode'
with 'accumulation', 'aitken', etc.
2) The question of the definition of aitken and coarse modes. It has
been agreed that the terms 'aitken mode' and 'coarse mode' are
sufficiently widely used to merit their inclusion in standard names.
However, Christiane on 23 November 2008, wrote:
>
>I think it is however impossible to prescribe the definition in CF as
>people use different limits in their model. Would it be possible to
>request the exact definition in the comment of this name? under
>discussion
>
This issue is similar to the question of how to deal with families of
chemical species. I think it would be OK to put something in the
definition that makes it clear that these quantities can vary between
models. Is the definition of 'accumulation mode' similarly vague?
3) In her original posting in this thread Heinke wrote:
>
> for variables TAU_MODE and ABS_MODE, we should remove atmosphere,
> because they are 3d, and in each model layer is given the optical
depth
> and is not the integration along the all atmosphere.
>
Am I correct in thinking that this remark refers to these
coarse/aitken/accumulation mode names? These comments seem to conflict
with the sentence in the current definition of optical_thickness which
reads 'The atmosphere optical thickness applies to radiation passing
through the entire atmosphere.'
One possibility would be to use 'atmosphere_layer' for these names as
follows:
optical_thickness_due_to_accumulation_mode_ambient_aerosol_in_atmosphere
_layer
optical_thickness_due_to_accumulation_mode_dry_insoluble_aerosol_in_atmo
sphere_layer.
However, others have expressed the view that atmosphere_layer names
should be deprecated in favour of using 'atmosphere' plus a vertical
coordinate bounds variable. This has been discussed earlier in the
ECHAM5-hammoz thread and in the medium 'atmosphere' thread. It seems
appropriate here to include the discussion of the existing name
optical_thickness_of_atmosphere_layer_due_to_aerosol which took place in
the 'Modification of some existing CF standard names for chemical
constituents' thread.
Christiane wrote:
> -> old: optical_thickness_of_atmosphere_layer_due_to_aerosol
> FROM ME
> >> The other optical thickness names are built like this:
> >> atmosphere_optical_thickness_due_to_X
> >> For consistency, I would suggest to change the first name to
> >> atmosphere_layer_optical_thickness_due_to_aerosol
> >
> FROM JONATHaN
> > I don't agree with that because all the existing 31 names with
> > atmosphere_layer
> > have of_atmosphere_layer or in_atmosphere_layer. However I have
thought
> > for some time that we don't really need the "atmosphere layer"
names. We
> > could just specify "atmosphere" and allow the bounds of the vertical
> > coordinate to indicate what layer it means. That would be a
simplification.
>
> Maybe we could alias this name with
> atmosphere_optical_extinction_due_to_X because usually optical
thickness
> refers to the whole column of the atmosphere and is the vertical
> integral the extinction. This way, the layer-question would vanish and
> the name would be more physical.
I wonder whether Christiane's approach could be used for these mode
names, which would give us names of the form:
atmosphere_optical_extinction_due_to_accumulation_mode_ambient_aerosol
atmosphere_optical_thickness_due_to_accumulation_mode_dry_insoluble_aero
sol
I would welcome further comments on these names and definitions.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Fax: +44 1235 446314
Rutherford Appleton Laboratory Email: alison.pamment at stfc.ac.uk
Chilton, Didcot, OX11 0QX, U.K.
--
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Received on Mon Mar 30 2009 - 05:43:16 BST
