[CF-metadata] new standard names for surface aerosol optical properties

Markus Fiebig Markus.Fiebig at nilu.no
Mon Mar 12 09:07:49 MDT 2012


Hi Philip,

thanks for doing such a thorough job reviewing my proposal! Indeed, I should have seen a few of the points you mention even before I posted my proposed standard names. I therefore included, below my comments, an updated version of my proposed list of standard names and pertaining definitions.

For the sake of ease, I put my comments inline below your items.

Best regards,
Markus


Some general comments:

1) There is no mention of frequency in your definitions.  This is true for some of the existing std_name definitions too.  However, I note that the description of some of the existing std_names (eg atmosphere_absorption_optical_thickness_due_to_ambient_aerosol) contains the following, which I recommend that we include in all your definitions (CF is used for everything from UV to radio waves): "A coordinate variable of radiation_wavelength or radiation_frequency can be specified to indicate that the optical thickness applies at specific wavelengths or frequencies."

MF: Yes, after I posted my proposal, I discovered these examples too. I will add this sentence to all spectral properties.

2) Do you really mean _due_to_dry_aerosol?  I interpret this to mean in a humid atmosphere you are quantifying the scattering that would occur if, hypothetically, the aerosols were dry rather than their actual ambient state.

MF: Yes, this interpretation is correct. With few exceptions, the standard operating procedures (SOP) of ground-based aerosol optical property networks say that the sample is led into an instrument container or cabin that is climatised roughly to lab temperature. Other approaches would be too costly. That implies that the aerosol humidity state is altered anyway from the ambient state. To make measurements comparable and easier to interpret, it is thus specified that the sample should be dried to < 40% RH. I will add a corresponding sentence to the definitions. Do you think the standard name needs to be adapted as well, or is it sufficiently "self-explaining"?

3) For the terms with _due_to_pm1(10)_dry_aerosol, is the pm1(10) selection on ambient aerosol of dry aerosol?

MF: Good point, even though my answer won't satisfy. This isn't finally concluded in the current SOPs, and both practices are being used. This is where current observations are a little "unclean".

3) Dry aerosol is usually described for std_names as '"Dry aerosol" means aerosol without water'.  Your description is possibly better, but you might consider going with the former for consistency.

MF: The wording I used describes what is used on the experimental side, so likely what the files will contain. I will have a look to make the wording more consistent.

4) I am not sure what you mean by surface_volume_ .

MF: I was previously being told that the "volume" term needs to be part of a scattering_coefficient if the property refers to a volume of air as opposed to a surface. The "surface" preceding the "volume" on my proposed variable names is a qualification, and refers to the location , i.e. the lower bound of the atmosphere.

5) You mention that _hemispheric_backscattering_ is scattering into the 'rearward hemisphere relative to the incident beam'.  This appears to be the same definition that is already given to both _backscattering_ (eg, backscattering_ratio, histogram_of_backscattering_ratio_over_height_above_reference_ellipsoid) and _backwards_scattering_ (eg, surface_backwards_scattering_coefficient_of_radar_wave, volume_attenuated_backwards_scattering_function_in_air_assuming_no_aerosol_or_cloud).  Hence, it appears that we already have duplicate terms in the std_name table.  We should probably pick a preferred option, and fix the other one with aliases.

MF: This is going to be a tough one, especially since several communities with engrained customs are involved. I chose hemispheric in hemispheric_backscattering_coefficient, which is integrated over the rearward hemisphere as measured by some integrating nephelometers, from the backscattering_coefficient that isn't integrated over any solid angle (to be proposed soon), e.g. as measured by a lidar. In the examples you mention however, the term "backscattering" is already used for a property integrated over a solid angle. I've pondered over this one quite a while, but I keep coming back to the point that a standardised word for distinguishing angular integrated from non-angular integrated properties is needed - like "hemispheric". That wouldn't be a nice solution, since it implied aliases for 5 existing standard names. Any better ideas?

6) We currently don't have any std_names with _due_to_aerosol.  They all specify either _ambient_ or _dry_.

MF: The reason why I didn't write "ambient" or "dry" here is that some data is neither nor. As written above, the sample is usually fed into a lab container (implicit warming) and dried (by diffusion dryer). Some sites, e.g. (sub)-tropical ones in summer, don't manage to dry the sample to < 40% RH. For these sites, the humidity state needs to be given in the file since it varies (I will correct the corresponding sentence in the definition), but it is neither dry nor ambient.

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Updated list of proposed standard names (2012-03-12)

1) volume_scattering_coefficient_in_air_due_to_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


2) volume_absorption_coefficient_in_air_due_to_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


3) volume_hemispheric_backscattering_coefficient_in_air_due_to_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


4) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometer. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


5) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


6) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


7) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


8) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


9) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "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 fully dehydrated from its ambient state, experimentally brought to a relative humidity less than 40%. 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


10) volume_scattering_coefficient_in_air_due_to_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


11) volume_absorption_coefficient_in_air_due_to_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


12) volume_hemispheric_backscattering_coefficient_in_air_due_to_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


13) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometer. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


14) surface_volume_scattering_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume scattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


15) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


16) surface_volume_absorption_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume absorption coefficient is the fractional change of radiative flux per unit path length due to absorption of an incident light beam by a component in the reference volume. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


17) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm1" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 1 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


18) surface_volume_hemispheric_backscattering_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume hemispheric backscattering coefficient is the fractional change of radiative flux per unit path length due to redirection of an incident light beam into the rearward hemisphere relative to the incident beam by a component in the reference volume. It is distinct from the backscattering coefficient which isn't integrated over the rearward hemisphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Aerosol" without further qualification such as dry or ambient means that the aerosol humidity state is neither dry nor ambient and stated in the data. To specify the relative humidity at which the property applies, provide scalar coordinate variable with the standard name of "relative_humidity". 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. "surface" means the lower boundary of the atmosphere. "at_stp" refers to a volume at standard conditions of temperature (273.15 K) and pressure (1013.25 hPa). "pm10" refers to the fraction of aerosol particles with an aerodynamic diameter of less than or equal to 10 micrometers. A coordinate variable of radiation_wavelength or radiation_frequency needs to be specified to indicate that the property applies at specific wavelengths or frequencies.


 _______________________________________
 Dr. Markus Fiebig

 Dept. Atmospheric and Climate Research (ATMOS) Norwegian Institute for 
 Air Research (NILU) P.O. Box 100
 N-2027 Kjeller
 Norway

 Tel.: +47 6389-8235
 Fax : +47 6389-8050
 e-mail: Markus.Fiebig at nilu.no
 skype: markus.fiebig



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