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#81 fixed new standard names for surface aerosol optical properties cf-standard-names@… markus
Description

Dear all,

since the WMO Global Atmosphere Watch (GAW) programme is moving towards using CF standard names as standard vocabulary, I'd like to propose the following standard names that represent aerosol properties being observed at the GAW surface sites:

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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). "Dry aerosol" is aerosol at a relative humidity < 40% where it hasn't taken up ambient water by hygroscopic growth. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

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 stated in the data. 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.

#8 fixed Identifying horizontal coordinate variables using the axis attribute cf-conventions@… jonathan
Description

1. Title

Identifying horizontal coordinate variables using the axis attribute

2. Moderator

Russ Rew

3. Requirement

A method is needed to identify which are the horizontal coordinate axes of a data variable

4. Initial Statement of Technical Proposal

The axis attribute of coordinate variables (1D, in the Unidata sense) is optional. The value axis="X" can be used on a longitude coordinate variable (CF 4.2), and axis="Y" on a latitude coordinate variable (CF 4.1) (case-insensitive). CF is ambiguous about its use on other coordinate variables. The introduction of CF 4 states that the axis attribute is recommended for other kinds of spatial coordinate, but without giving an interpretation to its values. However in CF 4.1 and 4.2 it is prohibited for coordinate variables of rotated latitude and longitude. This proposal aims to clarify the use of the axis attribute for horizontal coordinate variables.

The proposal is

  • to modify the sentence "We attach no specific meaning ..." in the introduction to CF 4 with: "The values X and Y for the axis attribute should be used to identify horizontal coordinate variables. If both X- and Y-axis are identified, X-Y-up should define a right-handed coordinate system i.e. rotation from the positive X direction to the positive Y direction is anticlockwise if viewed from above."
  • to delete the prohibition on the axis attribute for rotated latitude in CF 4.1, and rotated longitude in CF 4.2.
  • to append the following to the paragraph beginning "The use of coordinate variables" in the introduction to CF 5: "The axis attribute is not allowed for auxiliary coordinate variables. Auxiliary coordinate variables which lie on the horizontal surface can be identified as such by their dimensions being horizontal, which can in turn be inferred from their having an axis attribute of X or Y, or from their units in the case of latitude and longitude (see section 4)."
  • to append the following to the paragraph beginning "If the coordinate variables" in the introduction to CF 5: "The use of the axis attribute with values X and Y is recommended for the coordinate variables (see section 4)."

5. Benefits

The axis attribute, thus redefined, provides a clear way to identify horizontal coordinate variables and horizontal auxiliary coordinate variables.

As an example, we can modify the one in CF 5.2:

dimensions:
  xc = 128 ;
  yc = 64 ;
  lev = 18 ;
variables:
  float T(lev,yc,xc) ;
    T:long_name = "temperature" ;
    T:units = "K" ;
    T:coordinates = "lon lat" ;
  float xc(xc) ;
    xc:axis="X";
    xc:long_name = "x-coordinate in Cartesian system" ;
    xc:units = "m" ;
  float yc(yc) ;
    yc:axis="Y";
    yc:long_name = "y-coordinate in Cartesian system" ;
    yc:units = "m" ;
  float lev(lev) ;
    lev:long_name = "pressure level" ;
    lev:units = "hPa" ;
  float lon(yc,xc) ;
    lon:long_name = "longitude" ;
    lon:units = "degrees_east" ;
  float lat(yc,xc) ;
    lat:long_name = "latitude" ;
    lat:units = "degrees_north" ;

The axis attributes identify xc and yc as horizontal dimensions, and indicate that xc-yc-up is right-handed. Because xc and yc are the dimensions of lon and lat, these auxiliary coordinate variables are also implied to be horizontal. In this case, we can also deduce that from the fact that they are identifiable as longitude and latitude, but for a general 2D coordinate variable it might not be obvious.

There is no backward incompatibility because the redefinition permits the axis attribute in cases where it was formerly not allowed, but does not change its meaning in existing cases.

6. Status Quo

With the CF standard as it is, latitude and longitude coordinate variables can be identified by their units or standard_name, and they are well known to be horizontal. Other horizontal coordinate variables can be identified only by recognising specific standard_names e.g. those in Appendix F on map projections. The axis attribute is a more general solution that works without any knowledge of the possible choices of horizontal grid.

#9 wontfix Extensions to CF grid mapping attributes to support coordinate reference system properties cf-conventions@… pbentley
Description

1. Title

Proposed Extensions to CF Grid Mapping Attributes to support CRS Properties

2. Moderator

Jonathan Gregory

3. Requirement

Previous posts to the CF mailing list have identified the requirement for additional attributes that could be used to provide a fuller definition of the characteristics of the coordinate reference system (CRS) used by spatial coordinates within a netCDF file. This proposal attempts to define attributes for several commonly used CRS properties.

4. Initial Statement of Technical Proposal

Owing to the length of this proposal, the full specification text is included in the attached PDF document.

(NB: If it is considered more convenient, e.g. for discussion purposes, to upload the full text of this proposal into this Trac ticket, then the author is happy to do so.)

5. Benefits

Scope: potentially all producers and end-users of netCDF datasets could exploit the proposed new attributes.

New capabilities: the proposed new attributes would enable data producers to more accurately record the specific characteristics of the coordinate reference system (or systems) used to define spatial coordinates within netCDF files.

Example use-case 1: A data producer has collected meteorological observations using a sensor platform which uses, for example, a particular geodetic datum (e.g. WGS 84, NAD 83, OSGB 36) to record spatial coordinates. It is desirable for this piece of CRS metadata, and others like it, to be recorded in appropriate netCDF CF attributes.

Example use-case 2: A climate data center wishes to convert a legacy dataset to netCDF format and make it available over the internet. The legacy dataset is based upon an unusual or customised coordinate reference system (e.g. transverse mercator projection using, say, the Clarke 1880 ellipsoid). As before, these CRS details need to be encoded in agreed, standardised CF attributes.

6. Status Quo

The author is not aware of alternative CF attributes or mechanisms that could be used to encode the desired additional CRS properties.

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