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

From: Markus Fiebig <Markus.Fiebig>
Date: Wed, 21 Mar 2012 15:18:07 +0000

Hi Philip, hi Jonathan,

thanks for your constructive input! It seems we are circling in on most of the debated points. Even though it may seem cumbersome, I think it will be of great value to have variable names which are common between the modelling and observational communities. Please see my comments below. I also added a new version of my proposed variable names including the latest outcome of our discussions.

Best regards,
Markus

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> 3a) 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".

[PJC] I would naturally expect X in _pmX_dry_aerosol to be the size of the dried aerosol. If this is not what you need then we should probably change the std_name (I do not know of an analogous example in CF). Either way, the definition should make clear what is intended. FWIW, CF already has _pmX_ambient_aerosol.

MF: Precisely this point took a little discussion with my peers, which is why my answer comes so late. We came to the conclusion that the definition should state that the size cut applies to the aerosol at ambient conditions, the same as with pretty much all other CF variables containing pmX. The "_dry_aerosol" part will then refer to a drying of the aerosol after it has been size selected. Even though there is some variability in the installations used at various stations, they are equivalent with this definition within the experimental uncertainty. This might sound strange, but the question whether you have size selection or drying first isn't even the most critical here. You also have unavoidable variations in sample line length that cause at least as much systematic uncertainty for the size cut at the upper end of the selected size range. In short, the approach I suggest follows the philosophy that the variable is properly defined, and both model and measurement do their best to reach that definition.

> 3b) 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.

[PJC] Your wording is probably what most people mean by 'dry'. It is an explicit part of CF that the standard names are the physical quantity of interest, and instrument and models do their best to determine the quantity, even though they do so imperfectly. IMHO, this is one of the great advantages of CF, although it is hard. How about you use something like the following, '"Dry aerosol" means aerosol without water, which in practice often means ...'?

MF: I changed the wording accordingly in my latest update of the proposed set of variables.

> 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.

[PJC] I am still not sure I understand what you want. Is this some sort of surface albedo?

MF: I was modelling the proposed names on the existing CF variable "volume_extinction_coefficient_in_air_due_to_ambient_aerosol". In an earlier mail, Jonathan had the following remark on this:
"If I remember correctly, the terminology volume_*_coefficient was adopted for those with units of m-1, in contrast with those for scattering by a surface, which are dimensionless, and volume_*_function for those in m-1 sr-1."
Since all my proposed variables will have a unit of m-1, I included the volume_ in all of them. In addition, I needed to express that the location is at the lower boundary of the atmosphere. In CF syntax, this is expressed by a "surface_" qualifier preceeding the variable.

> 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_ellipsoi
> d
> ) and _backwards_scattering_ (eg,
> surface_backwards_scattering_coefficient_of_radar_wave,
> volume_attenuated_backwards_scattering_function_in_air_assuming_no_aer
> o sol_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?

[PJC] I have a strong dislike for having multiple terms mean the same thing in CF. When it does creep in I try to eliminate them. I also like to try and keep terms short, because std_names can get very long. CF already has _scattering_function_ for angle dependent scattering (eg, volume_scattering_function_of_radiative_flux_in_sea_water). On balance, I would use one of the existing terms (whichever CF decides is better).

MF: I changed the wording to _spherical_ in the latest version of the proposal as suggested by Jonathan.

> 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.

[PJC] This is a challenge because it puts two CF goals in conflict, ie accurately describing a variable and enabling quantities from different instruments and models to intercompare. To put it another way, the problem is that any data put into the std_name you suggest will be hard to use without additional information, since there is no way to know whether like quantities are being compared. Is it normal to have observation temperature and humidity data along with the aerosol measurements?

MF: I don't think this problem is as big as it might seem. Yes, it isn't unusual to pass along relative humidity together with an aerosol measurement. Just have a look at the definition of the "mass_concentration_of_pm2p5_ambient_aerosol_in_air" variable proposed by Martin Schultz which also includes relative humidity. Even though the variable name here states "ambient", any model / observation comparison will need to take the humidity effect into account since it is unlikely that modelled and observed humidity will match. In effect, this will be just the same with the variables I propose, only that the humidity given in the files won't be ambient and not necessarily, i.e. not always, dry (< 40%). Adding an "ambient_or_dry_aerosol" wouldn't be correct and would just add confusion, since the humidity ISN'T ambient and not always strictly dry.


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Updated list of proposed standard names (2012-03-21)

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, which in practice often means 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, which in practice often means 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_spherical_backscattering_coefficient_in_air_due_to_dry_aerosol

The volume spherical 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, which in practice often means 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, which in practice often means 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, where the size cut is applied under ambient conditions before the aerosol is dried. 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, which in practice often means 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, where the size cut is applied under ambient conditions before the aerosol is dried. 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, which in practice often means 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 e
qual to 1 micrometers, where the size cut is applied under ambient conditions before the aerosol is dried. 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, which in practice often means 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, where the size cut is applied under ambient conditions before the aerosol is dried. 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_spherical_backscattering_coefficient_at_stp_in_air_due_to_pm1_dry_aerosol

The volume spherical 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, which in practice often means 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 vo
lume 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, where the size cut is applied under ambient conditions before the aerosol is dried. 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_spherical_backscattering_coefficient_at_stp_in_air_due_to_pm10_dry_aerosol

The volume spherical 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, which in practice often means 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 vo
lume 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, where the size cut is applied under ambient conditions before the aerosol is dried. 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_spherical_backscattering_coefficient_in_air_due_to_aerosol

The volume spherical 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 o
r 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 le
ss than or equal to 1 micrometer, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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 l
ess than or equal to 10 micrometers, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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 les
s than or equal to 1 micrometers, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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 le
ss than or equal to 10 micrometers, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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_spherical_backscattering_coefficient_at_stp_in_air_due_to_pm1_aerosol

The volume spherical 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" ref
ers 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, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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_spherical_backscattering_coefficient_at_stp_in_air_due_to_pm10_aerosol

The volume spherical 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" ref
ers 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, where the size cut is applied under ambient conditions before aerosol humidity, pressure, or temperature are possibly altered. 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
Received on Wed Mar 21 2012 - 09:18:07 GMT