# 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

Default unit

absolute_vorticity

X

X

X

[1/s]

absorbing_aerosol_index

X

X

[]

aerosol_base_height

X

X

[m]

aerosol_base_pressure

X

X

[Pa]

aerosol_extinction_coefficient

surface

X

X

X

X

[1/m]

aerosol_height

X

X

[m]

aerosol_number_density

X

X

X

[1/m3]

aerosol_column_number_density

X

X

X

[1/m2]

aerosol_optical_depth

stratospheric, tropospheric

X

X

X

X

[]

this is equal to ‘aerosol optical thickness’

aerosol_pressure

X

X

[Pa]

aerosol_top_height

X

X

[m]

aerosol_top_pressure

X

X

[Pa]

<aerosol_size>_aerosol_number_density

X

X

X

[1/m3]

<aerosol_size>_aerosol_column_number_density

X

X

X

[1/m2]

<aerosol_size>_aerosol_extinction_coefficient

surface

X

X

X

X

[1/m]

<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

[m]

<aerosol_type>_aerosol_base_pressure

X

X

[Pa]

<aerosol_type>_aerosol_extinction_coefficient

surface

X

X

X

X

[1/m]

<aerosol_type>_aerosol_height

X

X

[m]

<aerosol_type>_aerosol_optical_depth

stratospheric, tropospheric

X

X

X

X

[]

this is equal to ‘aerosol optical thickness’

<aerosol_type>_aerosol_pressure

X

X

[Pa]

<aerosol_type>_aerosol_top_height

X

X

[m]

<aerosol_type>_aerosol_top_pressure

X

X

[m]

altitude

sensor, surface

X

X

X

[m]

altitude_bounds

X

X

X

[m]

angstrom_exponent

X

X

X

[]

area

X

[m2]

the size of an area defined by latitude/longitude bounds

backscatter_coefficient

surface

X

X

X

X

[1/m/sr]

cloud_albedo

X

X

[]

cloud_base_albedo

X

X

[]

cloud_base_height

X

X

[m]

cloud_base_pressure

X

X

[Pa]

cloud_base_temperature

X

X

[K]

cloud_fraction

X

X

[]

cloud_height

X

X

[m]

cloud_optical_depth

X

X

[]

this is equal to ‘cloud optical thickness’

cloud_pressure

X

X

[Pa]

cloud_temperature

X

X

[K]

cloud_top_albedo

X

X

[]

cloud_top_height

X

X

[m]

cloud_top_pressure

X

X

[Pa]

cloud_top_temperature

X

X

[K]

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

[kg/m2]

column_number_density

stratospheric, tropospheric

amf, apriori, avk, dfs, sic

X

X

X

[molec/m2]

count

number of samples per bin for binning/averaging

datetime

[s since 2000-01-01]

datetime_bounds

[s since 2000-01-01]

datetime_length

[s]

datetime_start

[s since 2000-01-01]

datetime_stop

[s since 2000-01-01]

density

X

X

X

[kg/m3]

extinction_coefficient

surface

X

X

X

X

[1/m]

frequency

X

X

[Hz]

frequency_bounds

X

X

[Hz]

X

X

[W/m2/Hz]

X

X

[1/s/m2/Hz]

X

X

[1/s/sr/m2/Hz]

frequency_photon_transmittance

X

X

[]

X

X

[W/sr/m2/Hz]

frequency_transmittance

X

X

[]

geoid_height

X

X

[m]

geopotential

surface

X

X

X

[m2/s2]

geopotential_height

surface

X

X

X

[m]

geopotential_height_bounds

X

X

X

[m]

gravity

surface

X

X

X

[m/s2]

hlos_wind_velocity

surface

X

X

X

[m/s]

hlos means ‘horizontal line of sight’

index

zero-based index of the sample within the source product

integration_time

X

X

X

[s]

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)

[degree_north]

latitude_bounds

(lat)

[degree_north]

location_name

name of the geographical location of the data

longitude

sensor

X

(lon)

[degree_east]

longitude_bounds

(lon)

[degree_east]

meridional_wind_velocity

surface

X

X

X

[m/s]

molar_mass

X

X

X

[g/mol]

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

[molec/m3]

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

[m]

potential_temperature

surface

X

X

X

[K]

pressure

surface

X

X

X

[Pa]

pressure_bounds

X

X

X

[Pa]

X

X

[W/sr/m2]

reflectance

X

X

[]

relative_azimuth_angle

X

[degree]

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

[degree]

scene_albedo

X

X

[]

scene_pressure

X

X

[Pa]

scene_type

X

X

sensor_azimuth_angle

X

[degree]

sensor_elevation_angle

X

[degree]

sensor_name

used mainly for ground based networks to provide a unique sensor id

sensor_zenith_angle

X

[degree]

solar_azimuth_angle

sensor, surface, toa

X

[degree]

solar_declination_angle

[degree]

solar_elevation_angle

sensor, surface, toa

X

[degree]

solar_hour_angle

[degree]

X

X

[W/m2]

solar_zenith_angle

sensor, surface, toa,

X

[degree]

X

X

[degree]

surface_albedo

X

X

X

[]

temperature

surface

X

X

X

[K]

tropopause_altitude

X

X

[m]

altitude of the troposphere/stratosphere boundary location

tropopause_pressure

X

X

[K]

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

[degree]

viewing_elevation_angle

X

[degree]

viewing_zenith_angle

X

[degree]

virtual_temperature

X

X

X

[K]

wavelength

X

X

[m]

wavelength_bounds

X

X

[m]

X

X

[W/m2/m]

X

X

[1/s/m2/m]

X

X

[1/s/sr/m2/m]

wavelength_photon_transmittance

X

X

[]

X

X

[W/sr/m2/m]

wavelength_transmittance

X

X

[]

wavenumber

X

X

[1/m]

wavenumber_bounds

X

X

[1/m]

X

X

[Wm/m2]

X

X

[m/s/m2]

X

X

[m/s/sr/m2]

wavenumber_photon_transmittance

X

X

[]

X

X

[Wm/sr/m2]

wavenumber_transmittance

X

X

[]

weekday

category variable for day of week (‘Monday’, …, ‘Sunday’)

week

integer value representing an ISO week number within a year (1, …, 53)

weekyear

integer value representing an ISO week year

weight

X

weighting factors used for binning/averaging

wind_speed

surface

X

X

X

[m/s]

wind_direction

surface

X

X

X

[degree]

year

integer value representing a year

zonal_wind_velocity

surface

X

X

X

[m/s]

<species>_column_density

stratospheric, tropospheric

amf, apriori, avk, dfs, sic

X

X

X

[kg/m2]

<species>_slant_column_density

X

X

[kg/m2]

<pm>_column_density

stratospheric, tropospheric

X

X

X

[kg/m2]

<species>_column_number_density

stratospheric, tropospheric

amf, apriori, avk, dfs, sic

X

X

X

[molec/m2]

<species>_slant_column_number_density

X

X

[molec/m2]

<species>_column_mass_mixing_ratio

stratospheric, tropospheric

X

X

[kg/kg]

<species>_column_mass_mixing_ratio_dry_air

stratospheric, tropospheric

X

X

[kg/kg]

<species>_column_volume_mixing_ratio

stratospheric, tropospheric

X

X

[ppv]

<species>_column_volume_mixing_ratio_dry_air

stratospheric, tropospheric

X

X

[ppv]

<species>_density

surface

X

X

X

[kg/m3]

<pm>_density

surface

X

X

X

[kg/m3]

O3_effective_temperature

X

X

[K]

<species>_mass_mixing_ratio

surface

apriori, avk, dfs, sic

X

X

X

[kg/kg]

<species>_mass_mixing_ratio_dry_air

surface

apriori, avk, dfs, sic

X

X

X

[kg/kg]

<species>_number_density

surface

apriori, avk, dfs, sic

X

X

X

[molec/m3]

<species>_partial_pressure

surface

X

X

X

[Pa]

<species>_partial_pressure_dry_air

surface

X

X

X

[Pa]

<species>_volume_mixing_ratio

surface

apriori, avk, dfs, sic

X

X

X

[ppv]

this is equal to ‘number mixing ratio’

<species>_volume_mixing_ratio_dry_air

surface

apriori, avk, dfs, sic

X

X

X

[ppv]

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).

surface quantities

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).

azimuth angles

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.

differences

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 ($$\frac{2|x-y|}{|x|+|y|}$$)

statistics

There are also ‘postfix’ variables available for statistics. HARP only provides naming conventions for statistical quantities that can be propagated (i.e. deriving statistics of a joined set of values based on statistics of disjoint subsets of those values). Quantities like count, standard deviation, skewness, kurtosis, minimum, and maximum, can be propagated, but median and IQR cannot. Variances should be stored as standard deviations. For the mean of a value, the original variable name itself is used. Other quantities are indicated by a postfix:

• <variable>_count

• <variable>_weight

• <variable>_stddev (sample standard deviation)

• <variable>_skewness

• <variable>_kurtosis

• <variable>_min

• <variable>_max

The ‘count’ and ‘weight’ are also available as variables on their own. The variable-specific postfix versions of ‘count’ and ‘weight’ should only be used when filtering out invalid values of a variable during binning/averaging would result in different count/weight values.

vertical profiles

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.