Guidelines for Construction of CF Standard Names

Guidelines for Construction of CF Standard Names

Version 1, 3 December 2008

Most of the CF standard names in the Standard Name Table have been constructed following the guidelines described here, which have themselves drawn on the ECMWF and NCEP GRIB tables, the PCMDI standard variable names, and the NASA Global Change Master Directory . The guidelines may help to interpret the names and to suggest how new names could be derived. Please send requests and questions concerning standard names to the CF metadata mailing list.


Standard names consist of lower-letters, digits and underscores, and begin with a letter. Upper case is not used.


US spelling is used e.g. vapor, sulfur.


Standard names may be qualified by the addition of phrases in certain standard forms and order. These qualifications do not change the units of the quantity. All of the following phrases in [] are optional. The words in typewriter type appear explicitly as stated, while the words in italic indicate other words or phrases to be substituted. The new standard name is constructed by joining the base standard name to the qualifiers using underscores.

[surface] [component] standard_name [at surface] [in medium] [due to process] [assuming condition]


A surface is defined as a function of horizontal position. Surfaces which are defined using a coordinate value (e.g. height of 1.5 m) are indicated by a single-valued coordinate variable, not by the standard name. In the standard name, some surfaces are named by single words which are placed at the start: toa (top of atmosphere), tropopause, surface. Other surfaces are named by multi-word phrases put after at: at_adiabatic_condensation_level, at_cloud_top, at_convective_cloud_top, at_cloud_base, at_convective_cloud_base, at_freezing_level, at_ground_level, at_maximum_wind_speed_level, at_sea_floor, at_sea_ice_base, at_sea_level, at_top_of_atmosphere_boundary_layer, at_top_of_atmosphere_model, at_top_of_dry_convection. The surface called "surface" means the lower boundary of the atmosphere. sea_level means mean sea level, which is close to the geoid in sea areas. ground_level means the land surface (beneath the snow and surface water, if any). cloud_base refers to the base of the lowest cloud. cloud_top refers to the top of the highest cloud. Fluxes at the top_of_atmosphere_model differ from TOA fluxes only if the model TOA fluxes make some allowance for the atmosphere above the top of the model; if not, it is usual to give standard names with toa to the fluxes at the top of the model atmosphere.


The direction of the spatial component of a vector is indicated by one of the words upward, downward, northward, southward, eastward, westward, x, y. The last two indicate directions along the horizontal grid being used when they are not true longitude and latitude (if there is a rotated pole, for instance). If the standard name indicates a tensor quantity, two of these direction words may be included, applying to two of the spatial dimensions Z Y X, in that order. If only one component is indicated for a tensor, it means the flux in the indicated direction of the magnitude of the vector quantity in the plane of the other two spatial dimensions.

The names of vertical components of radiative fluxes are prefixed with net_, thus: net_downward and net_upward. This treatment is not applied for any kinds of flux other than radiative. Radiative fluxes from above and below are often measured and calculated separately, the "net" being the difference. Within the atmosphere, radiation from below (not net) is indicated by a prefix of upwelling, and from above with downwelling. For the top of the atmosphere, the prefixes incoming and outgoing are used instead.


A medium indicates the local medium or layer within which an intensive quantity applies: in_air, in_atmosphere_boundary_layer, in_mesosphere, in_sea_ice, in_sea_water, in_soil, in_soil_water, in_stratosphere, in_thermosphere, in_troposphere.


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. Possibilites are: due_to_advection, due_to_convection, due_to_deep_convection, due_to_diabatic_processes, due_to_diffusion, due_to_dry_convection, due_to_gravity_wave_drag, due_to_gyre, due_to_isostatic_adjustment, due_to_large_scale_precipitation, due_to_longwave_heating, due_to_moist_convection, due_to_overturning, due_to_shallow_convection, due_to_shortwave_heating, due_to_thermodynamics (referring to sea ice freezing and melting).


A phrase assuming_condition indicates that the named quantity is the value which would obtain if all aspects of the system were unaltered except for the assumption of the circumstances specified by the condition. Possibilities are assuming_clear_sky, assuming_deep_snow, assuming_no_snow.


Standard names may be derived from other standard names (represented here by X, Y and Z) by the following rules. Successive transformations may be applied. Transformations may alter the units as shown.

Rule Units Meaning
change_over_time_in_X [X] change in a quantity X over a time-interval, which should be defined by the bounds of the time coordinate.
[horizontal_]convergence_of_X [X] m-1 [horizontal] convergence of a vector X (i.e. the divergence multiplied by -1); if X does not have a vertical component then "horizontal" should be omitted.
correlation_of_X_and_Y[_over_Z] 1 correlation coefficient for variations (over Z e.g. time, longitude) of X and Y. X and Y are ordered alphabetically.
covariance_of_X_and_Y[_over_Z] [X]*[Y] covariance for variations (over Z e.g. time, longitude) of X and Y. X and Y are ordered alphabetically.
component_derivative_of_X [X] m-1 derivative of X with respect to distance in the component direction, which may be northward, southward, eastward, westward, x or y. The last two indicate derivatives along the axes of the grid, in the case where they are not true longitude and latitude.
derivative_of_X_wrt_Y [X]/[Y] dX/dY (keeping any other independent variables constant, i.e. the partial derivative if appropriate).
direction_of_X degree direction of a vector, a bearing.
[horizontal_]divergence_of_X [X] m-1 [horizontal] divergence of a vector X; if X does not have a vertical component then "horizontal" should be omitted.
histogram_of_X[_over_Z] 1 histogram (i.e. number of counts for each range of X) of variations (over Z) of X. The data variable should have an axis for X.
integral_of_Y_wrt_X [X]*[Y] int Y dX. The data variable should have an axis for X specifying the limits of the integral as bounds.
ln_X 1 natural logarithm of X. X must be dimensionless.
log10_X 1 common logarithm (i.e. base 10) of X. X must be dimensionless.
magnitude_of_X [X] magnitude of a vector X.
probability_distribution_of_X[_over_Z] 1 probability distribution (i.e. a number in the range 0.0-1.0 for each range of X) of variations (over Z) of X. The data variable should have an axis for X.
probability_density_function_of_X[_over_Z] 1/[X] PDF for variations (over Z) of X. The data variable should have an axis for X.
product_of_X_and_Y [X]*[Y] X*Y. If X and Y are both scalars or both components of vectors, they are put in alphabetical order. If one of them is the component of a vector, it is put first i.e. the vector component is X, the scalar is Y.
ratio_of_X_to_Y [X]/[Y] X/Y.
square_of_X [X]*[X] X*X.
tendency_of_X [X] s-1 derivative of X with respect to time.

Special Phrases

Some words and phrases have meanings which should be noted.

Phrase Meaning
anomaly difference from climatology
area horizontal area unless otherwise stated
atmosphere used instead of in_air for quantities which are large-scale rather than local
condensed_water liquid and ice
frozen_water ice
longwave longwave radiation
lwe liquid water equivalent
moisture water in all phases contained in soil
ocean used instead of in_sea_water for quantities which are large-scale rather than local
shortwave shortwave radiation
specific per unit mass unless otherwise stated
stp standard temperature (0 degC) and pressure (101325 Pa)
toa top of atmosphere
unfrozen_water liquid and vapour
water water in all phases if not otherwise qualified
wrt with respect to

Chemical Species

The following names are used to identify chemical species in standard names.


Generic Names

The following names are used with consistent meanings and units as elements in other standard names, although they are themselves too general to be chosen as standard names. They are recorded here for reference only. These are not standard names.

Units Generic Name
kg m-2 amount
m2 area
1 area_fraction
1 binary_mask
1 data_mask
kg m-3 density
J energy
J m-2 energy_content
J m-3 energy_density
s-1 frequency
s-1 frequency_of_occurrence
W m-2 heat_flux
W heat_transport
m2 s-1 horizontal_streamfunction
m2 s-1 horizontal_velocity_potential
kg mass
kg m-2 s-1 mass_flux
1 mass_fraction
1 mass_mixing_ration
kg s-1 mass_transport
1 mole_fraction
mol m-2 s-1 mole_flux
Pa momentum_flux
Pa partial_pressure
s period
W power
Pa pressure
1 probability
W m-2 radiative_flux
m2 s-2 specific_eddy_kinetic_energy
m s-1 speed
Pa stress
K temperature
m thickness
m s-1 velocity
m3 volume
m s-1 volume_flux
1 volume_fraction
m3 s-1 volume_transport
s-1 vorticity