Variable names

To allow HARP to perform automatic operations on variables, it imposes a strict naming convention for variables. This naming convention applies to the variable name itself and is therefore fully complementary to naming conventions that apply to the value of a variable attribute, such as standard_name (as specified by netCDF-CF).

Note that it is possible to use variables inside HARP products with names that do not follow the convention, but then these variables may not be handled correctly by operations that you perform on the product. The general rule is that if you have a quantity that can be represented by the naming convention below then you should use the HARP variable name for it.

HARP defines the following variable names:

Name Prefixes Postfixes Quality Vert Lat/Lon Spect Comments
absolute_vorticity     X X X    
absorbing_aerosol_index     X   X    
aerosol_base_height     X   X    
aerosol_base_pressure     X   X    
aerosol_extinction_coefficient surface   X X X X  
aerosol_height     X   X    
aerosol_number_density     X X X    
aerosol_column_number_density     X X X    
aerosol_optical_depth stratospheric, tropospheric   X X X X this is equal to ‘aerosol optical thickness’
aerosol_pressure     X   X    
aerosol_top_height     X   X    
aerosol_top_pressure     X   X    
<aerosol_size>_aerosol_number_density     X X X    
<aerosol_size>_aerosol_column_number_density     X X X    
<aerosol_size>_aerosol_extinction_coefficient surface   X X X X  
<aerosol_size>_aerosol_optical_depth stratospheric, tropospheric   X X X X this is equal to ‘aerosol optical thickness’
<aerosol_type>_aerosol_base_height     X   X    
<aerosol_type>_aerosol_base_pressure     X   X    
<aerosol_type>_aerosol_extinction_coefficient surface   X X X X  
<aerosol_type>_aerosol_height     X   X    
<aerosol_type>_aerosol_optical_depth stratospheric, tropospheric   X X X X this is equal to ‘aerosol optical thickness’
<aerosol_type>_aerosol_pressure     X   X    
<aerosol_type>_aerosol_top_height     X   X    
<aerosol_type>_aerosol_top_pressure     X   X    
altitude sensor, surface   X X X    
altitude_bounds     X X X    
angstrom_exponent     X X X    
area     X       the size of an area defined by latitude/longitude bounds
backscatter_coefficient surface   X X X X  
cloud_albedo     X   X    
cloud_base_albedo     X   X    
cloud_base_height     X   X    
cloud_base_pressure     X   X    
cloud_base_temperature     X   X    
cloud_fraction     X   X    
cloud_height     X   X    
cloud_optical_depth     X   X   this is equal to ‘cloud optical thickness’
cloud_pressure     X   X    
cloud_temperature     X   X    
cloud_top_albedo     X   X    
cloud_top_height     X   X    
cloud_top_pressure     X   X    
cloud_top_temperature     X   X    
cloud_type     X   X    
collocation_index             zero-based index as provided in the collocation result file
column_density stratospheric, tropospheric amf, apriori, avk, dfs, sic X X X   this is the mass density
column_number_density stratospheric, tropospheric amf, apriori, avk, dfs, sic X X X    
count             number of samples per bin for binning operation
datetime              
datetime_length              
datetime_start              
datetime_stop              
density     X X X   this is the mass density
extinction_coefficient surface   X X X X  
frequency     X     X  
frequency_bounds     X     X  
frequency_irradiance     X     X  
frequency_photon_irradiance     X     X  
frequency_photon_radiance     X     X  
frequency_photon_transmittance     X     X  
frequency_radiance     X     X  
frequency_transmittance     X     X  
geoid_height     X   X    
geopotential surface   X X X    
geopotential_height surface   X X X    
geopotential_height_bounds     X X X    
gravity surface   X X X    
hlos_wind_velocity surface   X X X   hlos means ‘horizontal line of sight’
index             zero-based index of the sample within the source product
integration_time       X X X provides measurement specific integration time (at e.g. altitude or wavelength) compared to overal datetime_length; only use if integration time differs from datetime_length; integration_time longer than datetime_length that covers multiple datetime values means replication of measured value in time dimension
land_type     X   X    
latitude sensor   X   (lat)    
latitude_bounds         (lat)    
longitude sensor   X   (lon)    
longitude_bounds         (lon)    
meridional_wind_velocity surface   X X X    
molar_mass     X X X   this is the molar mass of the total substance (it is defined by the relation between the variables ‘density’ and ‘number_density’)
month             category variable for month of year (‘January’, …, ‘December’)
number_density surface   X X X    
optical_depth     X X X X this is equal to ‘optical thickness’
orbit_index             the absolute orbit number for data from polar orbiting satellites
planetary_boundary_layer_height     X   X    
potential_temperature surface   X X X    
pressure surface   X X X    
pressure_bounds     X X X    
radiance     X     X  
reflectance     X     X  
relative_azimuth_angle     X       absolute difference between sensor and solar azimuth angles
relative_humidity surface   X X X    
relative_vorticity     X X X    
scan_direction_type              
scan_subindex              
scattering_angle     X        
scene_albedo     X   X    
scene_pressure     X   X    
scene_type     X   X    
sensor_azimuth_angle     X        
sensor_elevation_angle     X        
sensor_name             used mainly for ground based networks to provide a unique sensor id
sensor_zenith_angle     X        
site_name             used for data of a specific named geographical location
solar_azimuth_angle sensor, surface, toa   X        
solar_declination_angle              
solar_elevation_angle sensor, surface, toa   X        
solar_hour_angle              
solar_irradiance     X     X  
solar_zenith_angle sensor, surface, toa,   X        
sun_normalized_radiance     X     X  
surface_albedo     X   X X  
temperature surface   X X X    
tropopause_altitude     X   X   altitude of the troposphere/stratosphere boundary location
tropopause_pressure     X   X   pressure level of the troposphere/stratosphere boundary location
validity             validity flag for each time sample or whole product; only to be used if validity flag is for multiple variables combined
viewing_azimuth_angle     X        
viewing_elevation_angle     X        
viewing_zenith_angle     X        
virtual_temperature     X X X    
wavelength     X     X  
wavelength_bounds     X     X  
wavelength_irradiance     X     X  
wavelength_photon_irradiance     X     X  
wavelength_photon_radiance     X     X  
wavelength_photon_transmittance     X     X  
wavelength_radiance     X     X  
wavelength_transmittance     X     X  
wavenumber     X     X  
wavenumber_bounds     X     X  
wavenumber_irradiance     X     X  
wavenumber_photon_irradiance     X     X  
wavenumber_photon_radiance     X     X  
wavenumber_photon_transmittance     X     X  
wavenumber_radiance     X     X  
wavenumber_transmittance     X     X  
weight         X   weighting factors used for spatial binning
wind_speed surface   X X X    
wind_direction surface   X X X    
year             integer value representing a year
zonal_wind_velocity surface   X X X    
<species>_column_density stratospheric, tropospheric amf, apriori, avk, dfs, sic X X X   this is the mass density
<species>_slant_column_density     X   X   this is the mass density
<pm>_column_density stratospheric, tropospheric   X X X   this is the mass density
<species>_column_number_density stratospheric, tropospheric amf, apriori, avk, dfs, sic X X X    
<species>_slant_column_number_density     X   X    
<species>_column_mass_mixing_ratio stratospheric, tropospheric   X   X    
<species>_column_mass_mixing_ratio_dry_air stratospheric, tropospheric   X   X    
<species>_column_volume_mixing_ratio stratospheric, tropospheric   X   X    
<species>_column_volume_mixing_ratio_dry_air stratospheric, tropospheric   X   X    
<species>_density surface   X X X   this is the mass density
<pm>_density surface   X X X   this is the mass density
O3_effective_temperature     X   X    
<species>_mass_mixing_ratio surface apriori, avk, dfs, sic X X X    
<species>_mass_mixing_ratio_dry_air surface apriori, avk, dfs, sic X X X    
<species>_number_density surface apriori, avk, dfs, sic X X X    
<species>_partial_pressure surface   X X X    
<species>_partial_pressure_dry_air surface   X X X    
<species>_volume_mixing_ratio surface apriori, avk, dfs, sic X X X   this is equal to ‘number mixing ratio’
<species>_volume_mixing_ratio_dry_air surface apriori, avk, dfs, sic X X X    

The supported aerosol sizes are:

Aerosol size Description
ultrafine particles < 0.1 um
fine particles < threshold, 0.5 um <= threshold <= 2.5 um
coarse particles > threshold, 0.5 um <= threshold <= 2.5 um

The supported aerosol types are:

Aerosol type Description
sea_salt sea salt
dust dust
organic_matter organic matter
black_carbon black carbon
sulphate sulphate

The supported PM (particulate matter) types are:

Name Description
PM1 particulate matter with d < 1 um
PM2p5 particulate matter with d < 2.5 um
PM10 particulate matter with d < 10 um

The supported species are:

Name Description Aliases (not used by HARP)
dry_air dry air  
BrO bromine oxide  
BrO2 bromine dioxide  
CCl2F2 dichlorodifluoromethane freon-12, CFC-12, R-12, F12
CCl3F trichlorofluoromethane freon-11, CFC-11, R-11, F11
CCl4 tetrachloromethane  
CF4 tetrafluoromethane CFC-14, F14
CHClF2 chlorodifluoromethane HCFC-22, R-22, F22
CH3Cl chloromethane, methyl chloride HCC-40, R-40
CH3CN acetonitrile, methyl cyanide  
CH3OH methanol  
CH4 methane  
CO carbon monoxide  
COF2 carbonyl fluoride  
COS carbonyl sulfide OCS
CO2 carbon dioxide  
C2H2 acetylene HCCH
C2H2O2 glyoxal OCHCHO, CHOCHO
C2H3NO5 peroxyacetyl nitrate PAN
C2H6 ethane  
C3H8 propane  
C5H8 isoprene  
ClNO3 chlorine nitrate  
ClO chlorine monoxide  
HCHO formaldehyde CH2O, H2CO
HCOOH formic acid HCO2H
HCN hydrogen cyanide  
HCl hydrogen chloride  
HF hydrogen fluoride  
HNO2 nitrous acid  
HNO3 nitric acid  
HNO4 peroxynitric acid  
HOCl hypochlorous acid  
HO2 hydroperoxyl  
H2O water  
H2O_161 water (H1/O16/H1 isotopes)  
H2O_162 water (H1/O16/H2 isotopes) HDO
H2O_171 water (H1/O17/H1 isotopes)  
H2O_181 water (H1/O18/H1 isotopes)  
H2O2 hydrogen peroxide  
IO hypoiodite  
IWC ice water content; H2O in clouds in ice state  
LWC liquid water content; H2O in clouds in liquid state  
NH3 ammonia  
NO nitric oxide  
NOCl nitrosyl chloride  
NO2 nitrogen dioxide  
NO3 nitrate  
N2 nitrogen gas  
N2O nitrous oxide NOS
N2O5 dinitrogen pentoxide  
OClO chlorine dioxide ClO2
OH hydroxyl  
O2 oxygen  
O3 ozone  
O3_666 ozone (O16/O16/O16 isotopes)  
O3_667 ozone (O16/O16/O17 isotopes)  
O3_668 ozone (O16/O16/O18 isotopes)  
O3_686 ozone (O16/O18/O16 isotopes)  
O4 tetraoxygen, oxozone  
RWC rain water content; H2O as rain  
SF6 sulfur hexafluoride  
SO2 sulfur dioxide  
SWC snow water content; H2O as snow/ice  

Variables for which a prefix and/or postfix is provided can have any of the given prefixes and/or any of the given postfixes (separated by underscores). It is not allowed to provide more than one prefix or more than one postfix. Variables having an ‘X’ in the Quality column can have any of the following additional versions of the variable (where <variable> can include any of the allowed prefix and/or postfix combinations):

  • <variable>_covariance
  • <variable>_uncertainty
  • <variable>_uncertainty_random
  • <variable>_uncertainty_systematic
  • <variable>_validity

Some examples of valid variable names are: tropospheric_O3_column_number_density, tropospheric_O3_column_number_density_apriori, O3_column_number_density_apriori, tropospheric_O3_column_number_density_uncertainty, O3_column_number_density_apriori_uncertainty.

The Vert, Lat/Lon, and Spec columns indicate whether a variable can be dependent on the vertical, latitude & longitude, and/or spectral dimensions (any variable can be dependent on the time dimension).

The ‘surface’ prefix should only be used when quantities are combined together with quantities that have a vertical dimension. If a product just contains surface quantities then don’t use a ‘surface’ prefix but just omit the vertical dimension and indicate the vertical level (i.e. location of the surface) using a ‘pressure’, ‘altitude’, and/or ‘geopotential_height’ variable.

Surface wind velocity variables are actually near-surface wind velocities (usually at surface_altitude + 10m).

All (horizontal) azimuth angles in HARP should follow the convention that 0 is North facing and the angle is increasing when moving Eastwards (i.e. clockwise). Wind direction follows the same rules as for azimuth angles (North = 0, East = 90 degrees), but the direction indicates where the wind is coming from.

In addition to the conventions above there can also be variables that describe a ‘difference’. These difference variables can only be used to describe differences of the same quantity between different datasets (‘x’ and ‘y’) and only for variables that have a unit. All difference variables in a single product should apply to the same datasets ‘x’ and ‘y’ (i.e. the difference variables should only reflect a single comparison of datasets; you should not combine one difference variable for ‘x-y’ and another for ‘x-z’ (even for different quantities) within the same product). A difference variable is indicated by a postfix. The ‘difference postfix’ can come before a ‘quality postfix’ if we are talking about the ‘quality of the difference’. If the ‘difference postfix’ comes after a ‘quality postfix’ then we are talking about the ‘difference of the quality quantity’. The supported differences are:

  • <variable>_diff (\(x-y\))
  • <variable>_diffrelx (\(\frac{x-y}{x}\))
  • <variable>_diffrely (\(\frac{x-y}{y}\))
  • <variable>_diffrelmin (\(\frac{x-y}{\min(x,y)}\))
  • <variable>_diffrelmax (\(\frac{x-y}{\max(x,y)}\))
  • <variable>_diffrelavg (\(\frac{2(x-y)}{x+y}\))
  • <variable>_diffabs (\(|x-y|\))
  • <variable>_diffabsrelx (\(\frac{|x-y|}{|x|}\))
  • <variable>_diffabsrely (\(\frac{|x-y|}{|y|}\))
  • <variable>_diffabsrelmin (\(\frac{|x-y|}{\min(|x|,|y|)}\))
  • <variable>_diffabsrelmax (\(\frac{|x-y|}{\max(|x|,|y|)}\))
  • <variable>_diffabsrelavg (\(\frac{2|x-y|}{|x+y|}\))

The postfix ‘avk’ is used for averaging kernels of atmospheric vertical profiles. An AVK that only depends once on the vertical dimension is a column averaging kernel, and an AVK that depends twice on the vertical dimension is a profile averaging kernel. The ‘amf’ postfix is used for air mass factors. The ‘dfs’ postfix is used for the ‘degree of freedom for signal’ for vertical profiles which equals the trace or diagonal of the two-dimensional AVK and provides information on the vertical resolution and information content of profiles. The ‘sic’ postfix is used for the ‘Shannon information content’ for vertical profiles which can be derived from the two-dimensional AVK.

Both ‘count’ and ‘weight’ can also be used as a postfix for other variables to describe the counts/weights for those variables based on filtering out the invalid values during binning.