[CF-metadata] Standard names for RFMIP and GeoMIP

From: Alison Pamment - UKRI STFC <alison.pamment>
Date: Thu, 21 Jun 2018 06:41:38 +0000

Dear Robert and Martin,

Thank you both for your quick replies. There are just two names still under discussion for RFMIP. The first is very close to agreement, while I think the second can now be accepted. For clarity I have written everything out in full.

6. CMIP6 short name albdiff.
Most recently proposed as:
surface_diffuse_shortwave_hemispherical_reflectance (1)
'The surface called "surface" means the lower boundary of the atmosphere. "Diffuse" radiation is radiation that has been scattered by particles in the atmosphere such as cloud droplets and aerosols. The term "shortwave" means shortwave radiation. Hemispherical reflectance is the ratio of the energy of the reflected to the incident radiation. This term gives the fraction of the surface_diffuse_downwelling_shortwave_flux_in_air which is reflected. If the diffuse radiation is isotropic, this term is equivalent to the integral of surface_bidirectional_reflectance over all incident angles and over all outgoing angles in the hemisphere above the surface. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation. Shortwave hemispherical reflectance is related to albedo, but albedo is defined in terms of the fraction of the full spectrum of incident solar radiation which is reflected. It is related to the hemispherical ref
lectance averaged over all wavelengths using a weighting proportional to the incident heat flux.'

To respond to Robert's points on this one:
> *) ?hemispheric? is an acceptable alternative to ?hemispherical?

We have existing terms that refer to 'spherical' (rather than 'spheric') irradiances, so for consistency with those I think it's better to stick with 'hemispherical' in the proposed name.

> *) Albedo does indeed refer to a spectral integral (http://glossary.ametsoc.org/wiki/Albedo). Reflectance is the correct term for a
> spectral subset.
> *) Bidirectional reflectance is normally a function of incoming and outgoing direction
> (http://glossary.ametsoc.org/wiki/Bidirectional_reflection_function). If the field in question is a scalar I don?t know how to interpret
> the request.
Thank you - I think we are all now agreed on these definitions. Certainly this is consistent with our existing definition of bidirectional_reflecance. We have never until now properly defined 'albedo' for existing names. In the discussion of LS3MIP proposals I think we agreed a brief definition as follows: 'Albedo is the ratio of outgoing to incoming shortwave irradiance.' I suggest we make this even clearer: 'Albedo is the ratio of outgoing to incoming shortwave irradiance, where 'shortwave irradiance' means that both the incoming and outgoing radiation are integrated across the solar spectrum.' (This definition would then also be applied to the LS3MIP names and to all existing albedo names). Does that sound okay?

> *) Radiation can be scattered, and so move from the direct beam to the diffuse field, by the gaseous atmosphere as well as by clouds
> and aerosols. (That?s the Rayleigh scattering that makes red sunsets and blue skies.) The long definition for
> surface_diffuse_shortwave_hemispherical_reflectance implies that scattering is only by particles and requires correction.

Thank you for pointing this out. This is a deficiency in our existing definition text for 'diffuse radiation'. I suggest we modify the sentence as follows: ' "Diffuse" radiation is radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols.' The corrected definition would also be applied to 5 existing 'diffuse' names.

> *) surface_diffuse_shortwave_hemispherical_reflectance is, as Martin notes, the integral of the diffuse radiation times the
> surface_bidirectional_reflectance integrated over all incoming and outgoing angles of radiation. In climate models we normally have
> only a single value describing the hemispheric average of the diffuse radiation, in which case we make assumptions about its angular
> distribution.

Thank you for providing this explanation. I think this confirms that we should include the sentence 'If the diffuse radiation is isotropic, this term is equivalent to the integral of surface_bidirectional_reflectance over all incident angles and over all outgoing angles in the hemisphere above the surface' in the definition. I agree with Martin that it is useful to explain the relationships between the various quantities.

Drawing all of this back together, this name would now be as follows:
surface_diffuse_shortwave_hemispherical_reflectance (1)
'The surface called "surface" means the lower boundary of the atmosphere. "Diffuse" radiation is radiation that has been scattered by gas molecules in the atmosphere and by particles such as cloud droplets and aerosols. The term "shortwave" means shortwave radiation. Hemispherical reflectance is the ratio of the energy of the reflected to the incident radiation. The quantity with standard name surface_diffuse_shortwave_hemispherical_reflectance gives the fraction of the surface_diffuse_downwelling_shortwave_flux_in_air which is reflected. If the diffuse radiation is isotropic, surface_diffuse_shortwave_hemispherical_reflectance is equivalent to the integral of surface_bidirectional_reflectance over all incident angles and over all outgoing angles in the hemisphere above the surface. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation. Shortwave hemispherical reflectance is related to albedo, but albedo is def
ined in terms of the fraction of the full spectrum of incident solar radiation which is reflected. It is related to the hemispherical reflectance averaged over all wavelengths using a weighting proportional to the incident heat flux.'

(I have made a couple of cosmetic changes to Martin's text, in addition to modifying the 'diffuse' definition as discussed above).

Is this okay?

11. Most recently proposed as:
scattering_asymmetry_factor_of_ambient_aerosol_particles (1)
?The scattering asymmetry factor is the ?angular integral of the aerosol scattering phase function weighted by the cosine of the angle with the incident radiation flux. The asymmetry coefficient is assumed to be an integral over all wavelengths, unless a coordinate of radiation_wavelength is included to specify the wavelength. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. To specify the relative humidity and temperature at which the quantity described by the standard name applies, provide scalar coordinate variables with standard names o
f "relative_humidity" and "air_temperature".?

To answer Robert?s points about this one:
> *) Aerosols are distinct from the gaseous atmosphere, so the sentence?
> "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself.?
> is incorrect; please omit the mention of the carrier gas.?

The sentence defining 'aerosol' is the standard definition text that we use for all names that include the term. This definition was agreed on the mailing list in 2014 (see http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2014/007677.html) following detailed discussion with aerosol scientists. Apparently, this is the correct 'text book' definition. However, I appreciate that the quantity being proposed refers only to the particulate component of the aerosol (as do almost all existing aerosol standard names). At the same time as adopting the definition of aerosol it was also agreed that we would use the term aerosol_particles in standard names to distinguish when we are referring only to the particles and not the carrier gas. The definition gives an explanation of 'ambient aerosol particles' in addition to the general definition of 'aerosol'. So, in summary, this name does conform to the agreed pattern for standard names.

> *) The asymmetry factor applies only to scattered radiation so ?asymmetry_factor_of_ambient_aerosol_particles? would suffice. The
> term is only used, as far as I know, to specify the optical properties of particles.?

I asked whether other forms of aerosol asymmetry may occur, but if you think confusion is unlikely then I am happy to write the name without further qualification. In the event that any names are proposed in the future that could perhaps be confused with this one, we can consider at that stage how to make the distinction.

So the final form of this name would be:
asymmetry_factor_of_ambient_aerosol_particles (1)
'The scattering asymmetry factor is the angular integral of the aerosol scattering phase function weighted by the cosine of the angle with the incident radiation flux. The asymmetry coefficient is assumed to be an integral over all wavelengths, unless a coordinate of radiation_wavelength is included to specify the wavelength. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. To specify the relative humidity and temperature at which the quantity described by the standard name applies, provide scalar coordinate variables with standard names o
f "relative_humidity" and "air_temperature".?

This name is accepted for publication in the standard name table and will be added in the 2nd July update.

Best wishes,
Alison

------
Alison Pamment Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival Email: alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.

From: Robert Pincus <Robert.Pincus at colorado.edu>
Sent: 20 June 2018 14:37
To: Juckes, Martin (STFC,RAL,RALSP) <martin.juckes at stfc.ac.uk>
Cc: Pamment, Alison (STFC,RAL,RALSP) <alison.pamment at stfc.ac.uk>; CF-metadata (cf-metadata at cgd.ucar.edu) <cf-metadata at cgd.ucar.edu>; Karl Taylor <taylor13 at llnl.gov>
Subject: Re: [CF-metadata] Standard names for RFMIP and GeoMIP

Dear Alison, dear Martin -?

It?s a little difficult to jump into the middle of the conversation so forgive me as I make points that will take some effort to organize.?

*) ?hemispheric? is an acceptable alternative to ?hemispherical??
*) Albedo does indeed refer to a spectral integral (http://glossary.ametsoc.org/wiki/Albedo). Reflectance is the correct term for a spectral subset.?
*) Bidirectional reflectance is normally a function of incoming and outgoing direction (http://glossary.ametsoc.org/wiki/Bidirectional_reflection_function). If the field in question is a scalar I don?t know how to interpret the request.?

*) Radiation can be scattered, and so move from the direct beam to the diffuse field, by the gaseous atmosphere as well as by clouds and aerosols. (That?s the Rayleigh scattering that makes red sunsets and blue skies.) The long definition for surface_diffuse_shortwave_hemispherical_reflectance implies that scattering is only by particles and requires correction.?

*) surface_diffuse_shortwave_hemispherical_reflectance is, as Martin notes, the integral of the diffuse radiation times the surface_bidirectional_reflectance integrated over all incoming and outgoing angles of radiation. In climate models we normally have only a single value describing the hemispheric average of the diffuse radiation, in which case we make assumptions about its angular distribution.?

*) Insolation refers to the direct beam at the top of the atmosphere.?

*) Aerosols are distinct from the gaseous atmosphere, so the sentence?
"Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself.?
is incorrect; please omit the mention of the carrier gas.?

*) The asymmetry factor applies only to scattered radiation so ?asymmetry_factor_of_ambient_aerosol_particles? would suffice. The term is only used, as far as I know, to specify the optical properties of particles.?

Have I answered the relevant questions? It might be easiest for me to comment on the current state of the definitions rather than the series of proposed revision.?

---
Robert Pincus
University of Colorado/NOAA Earth System Research Lab
http://cires.colorado.edu/researcher/robert-pincus
On Jun 20, 2018, at 9:02 AM, Martin Juckes - UKRI STFC <mailto:martin.juckes at stfc.ac.uk> wrote:
Dear Alison, Robert,
6 & 7: In the sentence "If the diffuse radiation is isotropic, this term [i.e.surface_diffuse_shortwave_hemispherical_reflectance] is equivalent to the ?integral of surface_bidirectional_reflectance over all incident angles and over all outgoing angles in the hemisphere above the surface", I did mean isotropic in the sense of the diffuse radiation being of equal strength in all directions. I'd be glad if Robert could confirm or correct my interpretation of the relationship between surface_diffuse_shortwave_hemispherical_reflectance and surface_bidirectional_reflectance. My reasoning is that diffuse radiation is not necessarily isotropic, and if it is not the hemispherical reflectance will differ from a simple average of the bidirectional reflectance. I would like to have some explanation of the relationship between the two terms as I feel that it contributes to the clarify of the definition.
11. The asymmetry refers to the scattering phase function asymmetry, so how about scattering_asymmetry_factor_of_ambient_aerosol_particles ?
regards,
Martin
________________________________
From: CF-metadata <mailto:cf-metadata-bounces at cgd.ucar.edu> on behalf of Alison Pamment - UKRI STFC <mailto:alison.pamment at stfc.ac.uk>
Sent: 20 June 2018 12:53
To: CF-metadata (mailto:cf-metadata at cgd.ucar.edu)
Subject: Re: [CF-metadata] Standard names for RFMIP and GeoMIP
Forwarding this message to the list.
------
Alison Pamment ????????????????????????????????Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival ???mailto:alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
-----Original Message-----
From: Pamment, Alison (STFC,RAL,RALSP)
Sent: 20 June 2018 12:49
To: Juckes, Martin (STFC,RAL,RALSP) <mailto:martin.juckes at stfc.ac.uk>; Robert Pincus <mailto:Robert.Pincus at colorado.edu>; Karl Taylor <mailto:taylor13 at llnl.gov>
Subject: RE: [CF-metadata] Standard names for RFMIP and GeoMIP
Dear Martin, Robert, Karl,
Thank you for commenting on these names - I think we are making good progress.
> 6 & 7 Reflectances
> I thought I saw an email yesterday from Robert confirming Karl's 
> opinion that we should not use albedo for reflectance in a particular 
> wavelength band.  I can't find that email today, but I believe it just confirmed Karl's point. Another way of stating the difference is that the hemispherical reflectance at any wavelength is the outgoing radiant heat flow divided by the incoming radiant heat flow, and averaging this ratio over wavelengths is not, in general, going to give the same result as the ratio of the averaged outgoing heat flow to the averaged incoming heat flow.
> 
> We can, I think, exploit existing terms to clarify the definition of 
> these new terms: for the diffuse case, do we have the fraction of r which is reflected? It would then make sense, I think, to name it "surface_diffuse_shortwave_hemispherical_reflectance".
>
> There is clearly some relationship to the exist term 
> surface_bidirectional_reflectance. Is it correct to say that the new term is the average of surface_bidirectional_reflectance over all incoming and outgoing angles in the hemisphere if, and only if, the diffuse radiation if isotropic?
> 
> If so, I suggest the following modified description: 
> 'The surface called "surface" means the lower boundary of the 
> atmosphere. "Diffuse" radiation is radiation that has been scattered 
> by particles in the atmosphere such as cloud droplets and aerosols. 
> The term "shortwave" means shortwave radiation. Hemispherical 
> reflectance is the ratio of the energy of the reflected to the 
> incident radiation. This term gives the fraction of the surface_diffuse_downwelling_shortwave_flux_in_air which is reflected. If the diffuse >radiation is isotropic, this term is equivalent to the  integral of surface_bidirectional_reflectance over all incident angles and over all outgoing 
> angles in the hemisphere above the surface. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the 
> wavelength or frequency, respectively, of the radiation. Shortwave hemispherical reflectance is related to albedo, but albedo is defined in terms 
> of the fraction of the full spectrum of incident solar radiation which is reflected. It is related to the hemispherical reflectance averaged over all 
> wavelengths using a weighting proportional to the incident heat flux.'
This version of the name looks good - we haven't used 'hemispherical' as a term before, but I agree that it makes more sense than 'spherical' in the case of a reflectance.
Thank you for improving the definition - it is good to explain the difference between albedo and reflectance. There are journal papers that describe methods for estimating surface albedo by integrating bidirectional reflectance measured from satellites viewing from many angles, so it would certainly seem reasonable to say that integrating that quantity over all directions would give a hemispherical reflectance. What exactly is meant by describing the diffuse radiation as 'isotropic'? Certainly it would be coming from all directions in the hemisphere - are we also implying that the intensity of the radiation needs to be the same in all directions for the relationship between bidirectional reflectance and hemispherical reflectance to be true?
This name is still under discussion.
> The corresponding "direct" term would be: 
> surface_direct_shortwave_hemispherical_reflectance. I've tried to 
> explain how this relates to 'The surface called "surface" means the lower boundary of the atmosphere. "Direct" (also known as "beam") radiation is radiation that has followed a direct path from the sun and is alternatively known as "direct insolation". The term "shortwave" means shortwave radiation. Hemispherical reflectance is the ratio of the energy of the reflected to the incident radiation.
> This term gives the fraction of the surface_direct_downwelling_shortwave_flux_in_air which is reflected. 
> It is equivalent to the surface_bidirectional_reflectance at the 
> incident angle of the incoming solar radiation and integrated over all 
> outgoing angles in the hemisphere above the surface. A coordinate 
> variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation. 
> Shortwave hemispherical reflectance is related to albedo, but albedo is defined in terms of the fraction of the full spectrum of incident solar 
> radiation which is reflected. It is related to the hemispherical reflectance averaged over all wavelengths using a weighting proportional to the 
> incident heat flux.'
Again this looks good - thank you for providing a clear definition. This name is accepted for inclusion in the standard name table and will be added in the July 2nd update.
8. CMIP6 short name sol.
For this quantity we have agreed to use the existing name toa_incoming_shortwave_flux (W m-2) 'The abbreviation "toa" means top of atmosphere. The term "shortwave" means shortwave radiation. The TOA incoming shortwave flux is the radiative flux from the sun i.e. the "downwelling" TOA shortwave flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
I will add the sentence 'A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation' to allow the use of wavelength as a dimension to describe bands.
9. CMIP6 short name aerext.
For this quantity we have agreed to use the existing name volume_extinction_coefficient_in_air_due_to_ambient_aerosol_particles (1).
I will add the sentence 'The scattering/absorption/attenuation/extinction coefficient is assumed to be an integral over all wavelengths unless a coordinate of "radiation_wavelength" or "radiation_frequency" is included to specify the wavelength' to the definition. This will allow the use of the bands dimension and make the definition consistent with those of other existing radiative coefficient names.
10. CMIP6 short name aerssa.
For this quantity we have agreed to use the existing name single_scattering_albedo_in_air_due_to_ambient_aerosol_particles (1).
11. Asymmetry factor
> For the asymmetry factor, Robert has confirmed that this is the quantity wanted rather than the backscatter fraction, so the definition needs to 
> be modified slightly:
> asymmetry_factor_of_ambient_aerosol_particles
> Does the following work?
> The asymmetry factor is the ?angular integral of the aerosol scattering phase function weighted by the cosine of the angle with the incident 
> radiation flux. The asymmetry coefficient is assumed to be an integral over all wavelengths, unless a coordinate of radiation_wavelength is 
> included to specify the wavelength. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their 
> carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and 
> relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water 
> through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. To specify 
> the relative humidity and temperature at which the quantity described by the standard name applies, provide scalar coordinate variables with 
> standard names of "relative_humidity" and "air_temperature".
Thank you for clarifying the definition of this quantity. I think we should say in the name what the asymmetry factor refers to - it could be describing the shape of the particle, for example, but here we are talking about radiative properties. Would radiative_asymmetry_factor_of_ambient_aerosol_particles
be acceptable?
This name is still under discussion.
Best wishes,
Alison
------
Alison Pamment ????????????????????????????????Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival ???mailto:alison.pamment at stfc.ac.uk
STFC Rutherford Appleton Laboratory
R25, 2.22
Harwell Oxford, Didcot, OX11 0QX, U.K.
________________________________________
From: Robert Pincus <mailto:Robert.Pincus at colorado.edu>
Sent: 14 June 2018 07:33
To: Juckes, Martin (STFC,RAL,RALSP)
Cc: Pamment, Alison (STFC,RAL,RALSP)
Subject: Re: [CF-metadata] Standard names for RFMIP and GeoMIP
Martin -
We do want the asymmetry parameter using the cosine-weighted integral; I'm sorry if we have implied differently. The standard name asymmetry_factor_of_ambient_aerosol_particles would be perfect.What we want is results only for ambient aerosol.
To inform future requests, yes, it would be sensible to ask for combinations such as e.g. asymmetry_factor_of_ambient_aerosol_particles_and_clouds . Combining asymmetry factors is unambiguous if one also knows the optical depth and single-scattering albedo of each component.
- Robert
On Jun 13, 2018, at 1:22 PM, Martin Juckes - UKRI STFC <mailto:martin.juckes at stfc.ac.uk> wrote:
Dear Robert,
we have a question about the RFMIP variable "aerasymbnd" for which you
requested the standard name
volume_spectral_asymmetry_factor_in_air_due_to_ambient_aerosol_particles.
Markus Fiebig commented that the definition you gave, which refers to
the ratio of backscattered to forward scattered radiation, usually
goes under the name "backscatter fraction", rather than asymmetry
factor, which is a cosine weighted integral (see
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2015/058422.html).<h
ttp://mailman.cgd.ucar.edu/pipermail/cf-metadata/2015/058422.html)>
Which do you want, asymmetry factor or backscatter fraction?
The phrase "X_due_to_Y" in a standard name implies that there is a quantity "X" which can be written as a sum of terms due to "Y" and other processes. Here, it looks to me as though we are looking at a property of the aerosol particles, so asymmetry_factor_of_ambient_aerosol_particles may be more appropriate. For the quantity which you want here, does it make sense to add contributions from different sources, e.g. asymmetry factor due to aerosol + asymmetry factor due to cloud ice?
regards,
Martin
________________________________
From: Juckes, Martin (STFC,RAL,RALSP)
Sent: 13 June 2018 13:09
To: Pamment, Alison (STFC,RAL,RALSP); CF-metadata
(mailto:cf-metadata at cgd.ucar.edu)
Subject: Re: [CF-metadata] Standard names for RFMIP and GeoMIP
Dear Alison,
Thank you for reviewing all these. The "_clear_sky_and_no_aerosol" names look good.
6. & 7.
For the albedo terms: You are right about "spectral": this was included because the CMIP6 variables which need this standard name are requested in spectral frequency bands, but the term requested is an albedo, not an albedo per unit wave-number.
I believe that "spherical" and "hemispherical" have distinct meanings when applied to radiation terms. From ISO 9288-1996 ["Thermal insulation - Heat transfer by radiation .."]: "hemispherical" is used for quantities which "are related to all directions along which a surface element can emit or receive radiation", which I think applies here. Spherical irradiance refers to the total irradiance incident on a point from all angles. Hence, I think we should stay with hemispherical reflectance. On the other hand, "surface hemispherical reflectance" and "surface albedo" appear to mean the same thing, and we already have "surface_albedo", so it may be better to use that phrase here. I had not looked into this enough before, so thank you for querying the original suggestion.
The surface_albedo term makes no reference to the wavelength at which it should be calculated, but I believe that it is generally considered to be a quantity associated with shortwave radiation. Hence, I suggest we can drop this qualifier -- but only if everyone agrees that surface_albedo should, at least by default, apply to solar radiation.
Finally, "downwelling" is redundant here, since it is implicit in the definition of surface albedo. After these simplifying assumptions, we could use:
direct_surface_albedo
and
diffuse_surface_albedo.
8:
Yes, this the associated CMIP6 variable is the total incoming shortwave flux in bands, so a new name is not needed.
9 & 10
volume_extinction_coefficient_in_air_due_to_ambient_aerosol_particles and single_scattering_albedo_in_air_due_to_ambient_aerosol_particles: I agree.
11
aerasym:
volume_spectral_asymmetry_factor_in_air_due_to_ambient_aerosol_particl
es "asymmetry factor" and "backscatter fraction" appear to be two well
defined terms. I'll check with Robert Pincus to see which one he wants.
Looking at this again, I'm concerned that the use of "due_to_" is not entirely correct here: both "asymmetry factor" and "backscatter fraction" are properties of the particles ... I don't think it is part of an additive collection of terms which the use of "due_to" appears to imply. Hence, accepting your comments about "volume" and "spectral", I suggest:
asymmetry_factor_of_ambient_aerosol_particles or
backscatter_fraction_of_ambient_aerosol_particles
regards,
Martin
________________________________
Alison Pamment - UKRI STFCalison.pamment at http://stfc.ac.uk
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Dear All,
Standard names were proposed some time ago for CMIP6 RFMIP and some of the names received a small amount of discussion back in 2016. However, none of the names were published at that time. Three names were proposed for GeoMIP as long ago as 2015, but strangely, although I have a copy of the GeoMIP email (which was addressed to the mailing list) it seems never to have actually appeared on the list. The RFMIP and GeoMIP quantities are similar, so I will address both in this message. I would particularly like some advice on RFMIP proposals 6 - 11.
GeoMIP
1. stratosphere_optical_thickness_due_to_ambient_aerosol_particles (1)
The same quantity was recently proposed for PMIP and added in Version 53 of the standard name table, so this one is done.
2. toa_outgoing_shortwave_flux_assuming_clear_sky_and_no_aerosol
(Wm-2) This is the same as RFMIP proposal 1 (see below), so I will deal with this one as part of the RFMIP request.
3. toa_outgoing_shortwave_flux_assuming_no_aerosol (W m-2) This
proposal is straight forward. We have one existing assuming_no_aerosol name, volume_attenuated_backwards_scattering_function_in_air_assuming_no_aerosol_or_cloud. The definition can be constructed from existing text:
'The abbreviation "toa" means top of atmosphere. The term "shortwave" means shortwave radiation. The TOA outgoing shortwave flux is the reflected and scattered solar radiative flux i.e. the "upwelling" TOA shortwave flux, sometimes called the "outgoing shortwave radiation" or "OSR". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition.'
This name is accepted for publication in the standard name table and has been included in this week's update.
RFMIP
1. toa_outgoing_shortwave_flux_assuming_clean_clear_sky (W m-2)
Jonathan commented (in 2016) that it would be preferable to say 'no_aerosol' rather than 'clean' (http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2016/059135.html). I have seen some offlist emails that indicate 'no_aerosol' is now being used in preference to 'clean' in the CMIP6 long names. Also, this is consistent with the one existing no_aerosol name and the GeoMIP proposals.
This one should therefore be as follows:
toa_outgoing_shortwave_flux_assuming_clear_sky_and_no_aerosol (W m-2)
'The abbreviation "toa" means top of atmosphere. The term "shortwave" means shortwave radiation. The TOA outgoing shortwave flux is the reflected and scattered solar radiative flux i.e. the "upwelling" TOA shortwave flux, sometimes called the "outgoing shortwave radiation" or "OSR". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds.'
This name, units and definition are consistent with existing names so it is accepted and has been added in this week's standard name table update.
This proposal has been around for a long time and there is a possibility that some data have been written with the original version of the name. For this reason I have added toa_outgoing_shortwave_flux_assuming_clean_clear_sky to the standard name table and then immediately turned it into an alias of toa_outgoing_shortwave_flux_assuming_clear_sky_and_no_aerosol. This has been achieved by updating the standard name table twice - both versions will be published this week. (The double update is necessary to keep in sync with the standard name publication process on the NERC Vocabulary Server). We don't usually publish two versions of a name almost simultaneously, but there is a precedent for treating long standing proposals in this way - for example it was done for some standard names arising from trac ticket 37 which took a couple of years to agree. This arrangement affects 5 names for RFMIP.
2. surface_downwelling_shortwave_flux_in_air_assuming_clean_clear_sky
(W m-2)
As for proposal 1, we should replace 'clean' with 'no_aerosol':
surface_downwelling_shortwave_flux_in_air_assuming_clear_sky_and_no_ae
rosol (W m-2) 'The surface called "surface" means the lower boundary of the atmosphere. Downwelling radiation is radiation from above. It does not mean "net downward". The term "shortwave" means shortwave radiation. Surface downwelling shortwave is the sum of direct and diffuse solar radiation incident on the surface, and is sometimes called "global radiation". When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds.'
This name, units and definition are consistent with existing names so it is accepted and will be added in this week's standard name table update. As for proposal 1, I have published the original version of the name and immediately turned it into an alias of the final version.
3. surface_upwelling_shortwave_flux_in_air_assuming_clean_clear_sky (W
m-2)
As for proposal 1, we should replace 'clean' with 'no_aerosol':
surface_upwelling_shortwave_flux_in_air_assuming_clear_sky_and_no_aero
sol (W m-2) 'The surface called "surface" means the lower boundary of the atmosphere. Upwelling radiation is radiation from below. It does not mean "net upward". The term "shortwave" means shortwave radiation. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds.'
This name, units and definition are consistent with existing names so it is accepted and will be added in this week's standard name table update. As for proposal 1, I have published the original version of the name and immediately turned it into an alias of the final version.
4. upwelling_shortwave_flux_in_air_assuming_clean_clear_sky (W m-2)
As for proposal 1, we should replace 'clean' with 'no_aerosol':
upwelling_shortwave_flux_in_air_assuming_clear_sky_and_no_aerosol (W
m-2) 'Upwelling radiation is radiation from below. It does not mean "net upward". The term "shortwave" means shortwave radiation. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds.'
This name, units and definition are consistent with existing names so it is accepted and will be added in this week's standard name table update. As for proposal 1, I have published the original version of the name and immediately turned it into an alias of the final version.
5. downwelling_shortwave_flux_in_air_assuming_clean_clear_sky (W m-2)
As for proposal 1, we should replace 'clean' with 'no_aerosol':
downwelling_shortwave_flux_in_air_assuming_clear_sky_and_no_aerosol (W
m-2) 'Downwelling radiation is radiation from above. It does not mean "net downward". The term "shortwave" means shortwave radiation. When thought of as being incident on a surface, a radiative flux is sometimes called "irradiance". In addition, it is identical with the quantity measured by a cosine-collector light-meter and sometimes called "vector irradiance". In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A phrase "assuming_condition" indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. "Clear sky" means in the absence of clouds.'
This name, units and definition are consistent with existing names so it is accepted and will be added in this week's standard name table update. As for proposal 1, I have published the original version of the name and immediately turned it into an alias of the final version.
Now I am coming to some even older proposals for RFMIP, dating from 2015. They received only one comment at the time and I think the names, units and definitions need some work. For two of the quantities I think we can probably use existing names. I hope Martin, Daniel and Robert will be able to advise on these proposals.
6. CMIP6 short name albdiff.
surface_spectral_hemispherical_reflectance_of_diffuse_shortwave_radiat
ion (1) I think we probably shouldn't say 'spectral' in the name. We used to have standard names that included 'spectral' but then we agreed to change them all to say 'per_unit_wavelength' or 'per_unit_wavenumber'. Per_unit_wavelength introduces a unit of m-1 and per_unit_wavenumber introduces a unit of (m-1)-1; I suspect neither is appropriate in this case. We can still add a sentence in the definition that would say something like 'The reflectance is assumed to be an integral over all wavelengths, unless a coordinate of radiation_wavelength or radiation_frequency is included to specify either the wavelength or frequency' to allow the quantity to be specified at different wavelengths or frequencies. We do this for quite a number of existing names.
We have an existing name downwelling_spherical_irradiance_in_sea_water defined as 'Downwelling radiation is radiation from above. It does not mean "net downward". Spherical irradiance is the radiation incident on unit area of a hemispherical (or "2-pi") collector. It is sometimes called "scalar irradiance". The direction (up/downwelling) is specified. Radiation incident on a 4-pi collector has standard names of "omnidirectional spherical irradiance".' This makes me think that we should refer to the proposed name as a 'spherical' rather than 'hemishpherical' reflectance - presumably it is the reflectance that would apply to any shortwave radiation arriving at the surface from any upward direction. Apart from the omnidirectional names, all the existing 'spherical' names include some sense of direction (upwelling or downwelling). Since the current proposal is for shortwave radiation incident at the surface, I suggest we need to say 'downwelling'.
We do have existing names for diffuse radiation, e.g. surface_diffuse_downwelling_shortwave_flux_in_air. We can just say 'shortwave' instead of 'shortwave radiation' because that would be explained in the definition.
Putting all this together, I think we would arrive at the following name, units and definition:
surface_diffuse_downwelling_shortwave_spherical_reflectance (1) 'The
surface called "surface" means the lower boundary of the atmosphere. "Diffuse" radiation is radiation that has been scattered by particles in the atmosphere such as cloud droplets and aerosols. Downwelling radiation is radiation from above. It does not mean "net downward". The term "shortwave" means shortwave radiation. Spherical reflectance is the reflectance of radiation incident on unit area of a hemispherical (or "2-pi") collector. Reflectance is the ratio of the energy of the reflected to the incident radiation. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation.'
What do others think?
7. CMIP6 short name albdir.
surface_spectral_hemispherical_reflectance_of_direct_shortwave_radiati
on (1)
We have one existing name for direct radiation, direct_downwelling_shortwave_flux_in_air.
Following similar arguments to proposal 6, I suggest this one should be:
surface_direct_downwelling_shortwave_spherical_reflectance (1) 'The
surface called "surface" means the lower boundary of the atmosphere. "Direct" (also known as "beam") radiation is radiation that has followed a direct path from the sun and is alternatively known as "direct insolation". Downwelling radiation is radiation from above. It does not mean "net downward". The term "shortwave" means shortwave radiation. Spherical reflectance is the reflectance of radiation incident on unit area of a hemispherical (or "2-pi") collector. Reflectance is the ratio of the energy of the reflected to the incident radiation. A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation.'
Do others agree?
8. CMIP6 short name sol.
toa_incoming_shortwave_flux_per_unit_wavelength (W m-2) If this is
intended to be a truly spectrally resolved quantity, then the name is correct, but as I mentioned for proposal 6 the units should be W m-2 m-1. We do have an existing name toa_incoming_shortwave_flux which is integrated across all shortwave frequencies.
If we leave the name as it is, then we would have:
toa_incoming_shortwave_flux_per_unit_wavelength (W m-2 m-1) 'The
abbreviation "toa" means top of atmosphere. The term "shortwave" means shortwave radiation. The TOA incoming shortwave flux is the radiative flux from the sun i.e. the "downwelling" TOA shortwave flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics. A coordinate variable for radiation wavelength should be given the standard name radiation_wavelength.'
If these units are not acceptable we could use the existing name
toa_incoming_shortwave_flux (W m-2) 'The abbreviation "toa" means top
of atmosphere. The term "shortwave" means shortwave radiation. The TOA incoming shortwave flux is the radiative flux from the sun i.e. the "downwelling" TOA shortwave flux. In accordance with common usage in geophysical disciplines, "flux" implies per unit area, called "flux density" in physics.'
The definition is the same except for the sentence about the coordinate variable. We could add a slightly softer version of that sentence, similar to the reflectance names, 'A coordinate variable of radiation_wavelength or radiation_frequency can be used to specify the wavelength or frequency, respectively, of the radiation.' This would allow wavelength to be used as a ?dimension, but wouldn't alter the units.
What do others think?
9. CMIP6 short name aerext.
volume_spectral_extinction_coefficient_in_air_due_to_ambient_aerosol_p
articles (1)
As with the reflectance proposals, we shouldn't say 'spectral' in the name and if we say 'per_unit_wavelength' it would alter the units. In fact, for this quantity I think we have an existing name that would do the job:
volume_extinction_coefficient_in_air_due_to_ambient_aerosol_particles
(1) 'The volume extinction coefficient is the fractional change of radiative flux per unit path length. Extinction is the sum of absorption and scattering, sometimes called "attenuation". "Extinction" is the term most commonly used at optical wavelengths whereas "attenuation" is more often used at radio and radar wavelengths. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. 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.'
Again, we could add an advisory sentence to the definition to say that a coordinate variable of radiation_wavelength can be specified. What do others think?
10. CMIP6 short name aerssa.
volume_spectral_single_scattering_albedo_in_air_due_to_ambient_aerosol
_particles (1)
This one is similar to proposal 9. Again we shouldn't say 'spectral' and there is the question of units. I think this is another one for which we have an existing name:
single_scattering_albedo_in_air_due_to_ambient_aerosol_particles (1)
'"Single scattering albedo" is the fraction of radiation in an incident light beam scattered by the particles of an aerosol reference volume for a given wavelength. It is the ratio of the scattering and the extinction coefficients of the aerosol particles in the reference volume. A coordinate variable with a standard name of radiation_wavelength or radiation_frequency should be included to specify either the wavelength or frequency. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. To specify the relative humidity and temperature at which the quantity described by the standard name applies, provide scalar coordinate variables with standard names of "relative_humidity" and "air_temperature". 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.'
As with proposal 9, we could add an advisory sentence to the definition to say that a coordinate variable of radiation_wavelength can be specified. What do others think?
11. CMIP6 short name aerasym.
volume_spectral_asymmetry_factor_in_air_due_to_ambient_aerosol_particl
es (1)
I am not really familiar with this quantity, but I note Markus Fiebig's comment (http://mailman.cgd.ucar.edu/pipermail/cf-metadata/2015/058422.html) when the names were originally proposed to the mailing list:
For the aerosol asymmetry factor / parameter, I'm familiar with the
definition as the cosine weighted angular integral of the aerosol
scattering phase function. For the property you describe, I know the term "backscatter fraction", i.e. the ratio of the integral over the scattering phase function in the backward hemisphere (backscatter coefficient) over the aerosol scattering coefficient.
It sounds like this one is a new quantity to standard names. Again, I don't think the name itself should say 'spectral'. ?Rather than 'factor' I would suggest the term 'coefficient' which is already used in existing names. Also, I don't know whether we really need 'volume' in this case - I think this refers to extinction along the path of the radiation and volume coefficients have units of m-1. Does the asymmetry factor refer to a single scattering event or to multiple events along a path? I suggest the name would be:
[volume_]asymmetry_coefficient_of_radiative_flux_in_air_due_to_ambient
_aerosol_particles (1) and the definition would be something like:
'The asymmetry coefficient is the ratio of forward to backward scattered radiative flux. The asymmetry coefficient is assumed to be an integral over all wavelengths, unless a coordinate of radiation_wavelength is included to specify the wavelength. 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. "Aerosol" means the system of suspended liquid or solid particles in air (except cloud droplets) and their carrier gas, the air itself. "Ambient_aerosol" means that the aerosol is measured or modelled at the ambient state of pressure, temperature and relative humidity that exists in its immediate environment. "Ambient aerosol particles" are aerosol particles that have taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the particles. To specify the relative humidity and temperature at which the quantity described by the standard name applies, provide scalar coordinate variables with standard names of "relative_humidity" and "air_temperature".'
What do others think?
Best wishes,
Alison
------
Alison Pamment ????????????????????????????????Tel: +44 1235 778065
NCAS/Centre for Environmental Data Archival ???Email: alison.pamment
at
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Received on Thu Jun 21 2018 - 00:41:38 BST