StandardNamesRules.rst

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*******************
Earth System Modeling (ESM) Standard Names
*******************

This document contains information about the rules used to create Standard Names
for use with Earth System Models. It describes the

* ESM Standard Name rules
* Standard Name qualifiers
* Other common standard name components
* Acronyms, abbreviations, and aliases
* Units

.. _Rules

ESM Standard Name Rules
========================

Constructing names
------------------

#. Standard names should be identical to those from the latest version
   of the `Climate and Forecast (CF) metadata
   conventions <https://cfconventions.org/standard-names.html>`_ unless
   an appropriate name does not exist in that standard, or the adoption
   of said names leads to inconsistencies in the naming convention.

#. When no suitable standard name exists in the CF conventions, the following guidelines should be followed for constructing a new name.
   The phrases in brackets are optional. The words in *italic* appear explicitly as stated,
   while the words in ``this font`` 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.

   [``transformation``] [``component``] [``non-instant time``] base_name [*in*/*of* ``medium``] [*at* ``level``] [*due_to* ``process``] [``non-current time``] [*assuming* ``condition``]

   This construction was originally based on rules set forth in the
   `CF guidelines <http://cfconventions.org/Data/cf-standard-names/docs/guidelines.html>`_,
   but have since evolved for better consistency and generality across a broader set of fields
   than was originally envisioned by the CF conventions. "``medium``" should be specified when
   the variable in question is a substance or other quantity contained within some other medium
   (e.g. for ``mole_fraction_of_ozone_in_air``, the base name is "ozone", while the medium is "air").
   "Transformation" refers to descriptors such as "``tendency_of``", "``log10``", or other operations or processes describing some transformation or adjustment of a variable; a detailed list of possible transformations can be found `later in this document <#transformations>`_.
   Other parts of the construction provide information about a variable's horizontal surface
   (e.g. ``at_cloud_base``), component (i.e. direction of variable, e.g. ``downward``), process (e.g.
   ``due_to_deep_convection``), or condition (e.g., ``assuming_clear_sky``). These qualifications do not
   change the units of the quantity. This is not an exhaustive list of qualifiers that may be needed for a given standard name;
   see subsequent rules below for more information.

   The following table provides a few concrete examples of standard names and how they are constructed
   with respect to the guideline template.

   `image of table providing standard name construction examples <https://raw.githubusercontent.com/wiki/ESCOMP/ESMStandardNames/images/standard_name_construction_examples.png>`_

   Note that "transformations" are a special case, where multiple transformations may be applied,
   and multiple quantities may be compared, operated on, etc. For transformations involving
   multiple quantities (e.g. ``ratio_of_X_to_Y``; see the `section on Transformations <#transformations>`_
   for more information), the above formula may be extended around multiple base names.

   `image of table providing standard name construction examples with multiple transformations <https://raw.githubusercontent.com/wiki/ESCOMP/ESMStandardNames/images/standard_name_transformation_examples.png>`_

   In the latter example, ``ln`` is operating on the quantity ``water_vapor_partial_pressure_assuming_saturation``,
   while ``derivative_of`` is a combined transformation of ``water_vapor_partial_pressure_assuming_saturation``
   and ``air_temperature``. When multiple transformations are present, a more detailed description
   should be provided in the ``description`` field to prevent any possible ambiguity.

Variable scope
--------------

#. Variables are current and instantaneous unless specified. Variables that are not
   current (e.g., previous timestep) or non-instantaneous (e.g., accumulated values)
   should have qualifiers in the standard name to describe what they represent.

#. For accumulated variables, or variables representing a change over some period of time, the
   following suffixes are available":

   * ``over_[time]`` indicates an accumulation or other change over the previous duration/time
   * ``reset_every_[date/time]`` an accumulation or other change reset every set duration/time
     since the start of the simulation
   * ``since_[date/time]`` indicates an accumulation or other change since a given date/time.

   Dates, times, and durations should follow the `ISO 8601 <https://en.wikipedia.org/wiki/ISO_8601>`
   international standard, modified only to use lowercase rather than uppercase letters. Note that
   the standard is slightly different for dates and times vs durations. For example:

   * ``accumulated_precipitation_over_pt3h`` accumulated precipitation over the last 3 hours
   * ``accumulated_precipitation_over_p1dt12h`` accumulated precipitation over the last 1 day 12 hours
   * ``accumulated_precipitation_reset_every_pt1h`` accumulated precipitation reset every 1 hour
   * ``accumulated_precipitation_reset_every_p1y`` accumulated precipitation reset every 1 year
   * ``accumulated_precipitation_reset_every_p2dt12h`` accumulated precipitation reset every 2 days, 12 hours
   * ``accumulated_precipitation_since_20230522t120000`` accumulated precipitation since May 22, 2023 at 12:00
   * ``accumulated_precipitation_since_20251225`` accumulated precipitation since December 25, 2025
   * ``accumulated_precipitation_since_t00`` accumulated precipitation since 00:00:00 (midnight)

#. By default (when not specified otherwise), variables are grid means or centers
   (defined by the host). If a variable is defined at a different physical location,
   a qualifier should be used to denote this. For example, to specify the vertical
   location of a variable with respect to vertical grid cells, the following variants
   are possible:

   * ``[variable]``, with no location suffix, is defined at vertical-cell centers or
     as vertical-cell averages.

   * ``[variable]_at_interfaces`` is defined at the interfaces between grid cells
     vertically, including the bottom-most and top-most interfaces.
   * ``[variable]_at_top_interfaces`` is defined at the interfaces between grid cells
     vertically, including the top-most interface *but excluding the bottom-most
     interface*.

   * ``[variable]_at_bottom_interfaces`` is defined at the interfaces between grid
     cells vertically, including the bottom-most interface *but excluding the
     top-most interface*.

   This implies that if ``[variable]`` is defined on ``n`` points vertically,
   ``[variable]_at_interfaces`` is defined on ``n+1`` points,
   ``[variable]_at_top_interfaces`` is defined on ``n`` points, and
   ``[variable]_at_bottom_interfaces`` is defined on ``n`` points.

#. If possible, qualifiers should be limited in order to allow for a wide
   applicability of the variable. In other words, don't qualify with ``_for_specific_context``
   unless a variable could not conceivably be used outside of the more
   narrowly-defined context or a variable without the scope-narrowing qualifiers
   already exists and cannot be reused.

   **Discouraged:** upward_virtual_potential_temperature_flux_for_mellor_yamada_janjic_surface_layer_scheme

   **Preferred:** upward_virtual_potential_temperature_flux

#. If there are two identical quantities from different schemes/processes that
   need to be kept apart, suitable qualifiers are added to the names of the processes.
   If one process is already established and more common than the other, then it is
   sufficient to only prefix the new process with a suitable qualifier. Example:
   ``due_to_convective_GWD`` and ``due_to_convective_whole_atmosphere_GWD``
   as discussed in https://github.com/ESCOMP/ESMStandardNames/issues/79.

Terminology
-----------

#. By default, *mixing_ratio* refers to mass mixing ratios. The description should
   explicitly specify that it refers to the *mass* mixing ratio.
   Mass mixing ratios should contain information regarding
   with respect to what quantity they are defined, and options are *wrt_dry_air*,
   *wrt_moist_air*, or *wrt_moist_air_and_condensed_water*, where *moist_air*
   refers to dry air plus vapor and *moist_air_and_condensed_water* refers
   to dry air plus vapor and hydrometeors.

   Use of the term *specific_humidity* should be avoided, as there is no consensus on
   whether it refers to *water_vapor_mixing_ratio_wrt_moist_air* or
   *water_vapor_mixing_ratio_wrt_moist_air_and_condensed_water*.
   *total_water* can be used to designate water in every form, i.e. water
   vapor plus condensed water.

   Volume mixing ratios should be qualified as *volume_mixing_ratio*.

#. By default, *mole_fraction_of_X_in_Y* refers to the total amount of *Y*. So, for example,
   *mole_fraction_of_ozone_in_air* refers to the total amount of (moist) air. (In the case of air,
   the default meaning is moist air, as described in the *mixing ratio* rule.) When this is not
   the case, a qualifier should be used to denote this. *e.g.*, *mole_fraction_of_ozone_in_dry_air*.

#. When referring to soil quantities,
   *volume_fraction* should be used to express the volumetric soil moisture.

#. Number concentration should appear as a prefix, that is, *number_concentration_of*. By default,
   number concentrations are specified per unit of volume. When they are specified per
   unit of mass, they should be written as *mass_number_concentration_of*.

#. By default, *precipitation* refers to the sum of all phases of precipitating hydrometeors,
   for example rain plus graupel plus hail.  The term *frozen_precipitation* refers to the
   sum of all frozen precipitating hydrometers, for example graupel plus hail (but not rain).
   Otherwise the standard name should explicitly state the type of hydrometeor(s) the
   named quantity represents (e.g. *graupel*).

#. By default, the term *cloud* refers to all cloud phases and cloud types. Otherwise
   an additional prefix or suffix should be added to the standard name specifying what kind(s)
   of clouds the variable represents (e.g. *ice_cloud* if only including glaciated clouds, or
   *cloud_at_500hPa* if only including clouds that exist at 500 hPa).

#. Spell out acronyms unless they are obvious to a vast majority of
   scientists/developers who may come across them. A list of currently-used
   aliases is below. Whenever such an alias exist, use the alias in the
   standard name and the full term in the description.

#. Chemical species in standard names should be denoted by chemical formulae (e.g. ``co2``,
   ``ch4``, ``c5h8``) or commonly accepted designations (e.g. ``cfc12``); generally when there are
   multiple options the shorter name is preferred. A few species with well-established and
   unambiguous common names (e.g. water, ozone) are also included. In all cases, the standard name
   should include specific details about the substance's chemical makeup, as well as the
   phase/state of matter if relevant; e.g. ``water_vapor``, ``liquid_h2so4``

#. If the ionization of the chemical species is relevant, "ionized" should be included in the standard
   name as a prefix to the substance; e.g. ``number_density_of_ionized_he`` for ionized helium. If
   relevant, the net ionization charge should be included as a prefix (in words, because +/- are
   not valid standard name characters); e.g. ``number_density_of_plus_1_ionized_he``

#. For control-oriented variables, there are a few different prefixes that should be used depending on
   the use case for that specific variable:

   +-------------------+-----------+-----------------------------------------------------------------------------------------------+
   | **Prefix**        |  **Type** | **Use case**                    | **Example**                                                 |
   +===================+===========+=================================+=============================================================+
   | `is_`             | `logical` | A flag indicating some state or | `is_mpi_root` indicates whether or not the code is running  |
   |                   |           | condition is true or false      | on the MPI root process                                     |
   +-------------------+-----------+-------------------------------- +-------------------------------------------------------------+
   | `do_`             | `logical` | A flag whose value directs some | `do_chemical_tracer_diagnostics` indicates to a physics     |
   |                   |           | behavior                        | scheme that it should compute chemical tracer diagnostics   |
   +-------------------+-----------+---------------------------------+-------------------------------------------------------------+
   | `identifier_for_` | `integer` | A parameter indicating some     | `identifier_for_noah_land_surface_scheme` is an integer     |
   |                   |           | state or condition              | identifying the Noah land surface model                     |
   +-------------------+-----------+---------------------------------+-------------------------------------------------------------+
   | `control_for_`    | `integer` | A control whose value directs   | `control_for_land_surface_scheme` is an integer identifying |
   |                   |           | some behavior                   | the land surface scheme type                                |
   +-------------------+-----------+---------------------------------+-------------------------------------------------------------+
   | `index_of_`       | `integer` | An index entry for an array     | `index_of_ice_vegetation_category` is an index describing   |
   |                   |           |                                 | the location of the ice vegetation category in the array of |
   |                   |           |                                 | vegetation categories                                       |
   +-------------------+-----------+---------------------------------+-------------------------------------------------------------+


#. **Disallowed terms:** A few terms are disallowed as standard name components for various reasons; mostly due to
   ambiguity.

   - ``specific_humidity`` Disallowed due to ambiguity and different definitions between different fields. See above section describing ``mixing_ratio`` for more information.
   - ``amount`` In most contexts this word is superfluous, and in all contexts it is non-descriptive. Consider a more specific term such as ``mass_content``

#. **Reserved names:** The prefix ``ccpp_`` is reserved for CCPP framework-provided variables.
   All other standard names should avoid the use of ``ccpp`` in their name.


.. _tech_specs:

Technical specifications
========================

#. The standard name dictionary consists of a number of individual XML elements:
   one ``standard_name`` element for each entry. A standard name entry consist of a ``name`` attribute
   that represents the variable name, and (optionally) a ``description`` attribute that gives
   a detailed description of what that name represents. Note that the ``description`` field is only
   provided for information and disambiguation only (though it should be unique), and does not need to be included for
   individual implementations of the standard names. This is not necessarily the same as the ``long_name`` entry as described
   in the `CCPP Technical Documentation <https://ccpp-techdoc.readthedocs.io/en/latest/CompliantPhysicsParams.html#ccpp-arg-table>`_,
   but it can be used to inform the contents of that field. The ``standard_name`` XML entry also contains a nested
   ``type`` entry, indicating the data type that a ``standard_name`` should represent, and as an attribute the
   physical units of that variable quantity (see the `section on Units <#units>`_). For example, the element
   for the variable name ``exner_function`` may look similar to this:

    <standard_name name="exner_function"
                   description="exner function, (p/p0)^(Rd/cp), where p0 is 1000 hPa">
      <type units="1">real</type>
    </standard_name>

   This XML element indicates that the variable ``exner_function`` represents the quantity described by the ``description``
   attribute. It is a real variable with units of "1", meaning it is non-dimensional and
   does not correspond to a more descriptive non-dimensional type such as "fraction"; see the `section on Units <#units>`_
   for more details.

   The standard_name elements are grouped into sections by "section" elements. These are parsed out into human-readable sections
   in the generated markdown file (``Metadata-standard-names.md``). Sections can contain nested sections for further categorization.
   Standard Names should be sorted alphabetically by name within a given section. A python tool ``tools/sort_standard_names.py`` is
   provided to sort the names automatically.

#. Only alphanumeric, punctuation, and whitespace characters from the ASCII character set may be used in the standard_names dictionary.
   The "name" attributes of ``standard_name`` entries (i.e. the standard names themselves) are further restricted to the character set of capital/lowercase letters, numerals, and ``_`` (underscore).

#. The `<type>` element should include a value that is one of the following valid Fortran types:

   - ``integer``
   - ``real``
   - ``logical``
   - ``character``
   - ``complex``
   - ``ddt`` (derived data type)

#. The standard name dictionary XML file should validate according to the schema file ``standard_names.xsd`` All of the above specifications should be coded into this schema file as is appropriate.

.. _qualifiers:

Qualifiers
========================

``this font`` = words or phrases to be substituted

XY-surface
----------

Prefixes
^^^^^^^^

None. Note that this is a departure from the CF conventions, which in
many cases - but not all - use surface_ as a prefix. This departure from
the CF convention is to maintain consistency with all other level
qualifiers that are used as _at_level-qualifier (i.e. as suffix).

Suffixes
^^^^^^^^

| 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_ice_base
| at_sea_level
| at_top_of_atmosphere_boundary_layer
| at_top_of_atmosphere_model
| at_top_of_dry_convection
| at_interfaces
| at_toa
| at_tropopause
| at_surface
| at_surface_adjacent_layer
| at_2m
| at_10m
| at_bottom_interface
| at_pressure_levels
| at_top_of_viscous_sublayer
| at_various_atmosphere_layers
| extended_up_by_1


Component
---------

Prefixes
^^^^^^^^

| upward
| downward
| northward
| southward
| eastward
| westward
| x
| y

Special Radiation Component
---------------------------

Prefixes
^^^^^^^^

| net
| upwelling
| downwelling
| incoming
| outgoing

Medium
------

Suffixes
^^^^^^^^

| 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
| in_atmosphere
| in_surface_snow
| in_diurnal_thermocline
| in_canopy
| in_lake
| in_aquifer
| in_aquifer_and_saturated_soil
| in_convective_tower
| between_soil_bottom_and_water_table

Process
-------

Suffixes
^^^^^^^^

| due_to_advection
| due_to_convection
| due_to_deep_convection
| due_to_diabatic_processes
| due_to_diffusion
| due_to_dry_convection
| due_to_gwd
| due_to_convective_gwd
| due_to_convective_whole_atmosphere_gwd
| due_to_orographic_gwd
| 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_pbl_processes
| due_to_shortwave_heating
| due_to_thermodynamics
| due_to_background
| due_to_subgrid_scale_vertical_mixing
| due_to_convective_microphysics
| due_to_model_physics
| due_to_shoc
| due_to_dynamics

Condition
---------

Suffixes
^^^^^^^^

| assuming_clear_sky
| assuming_deep_snow
| assuming_no_snow
| over_land
| over_ocean
| over_ice
| for_momentum
| for_heat
| for_moisture
| for_heat_and_moisture
| assuming_shallow
| assuming_deep

Time
----

Suffixes
^^^^^^^^

| of_new_state
| on_physics_timestep
| on_dynamics_timestep

| on_radiation_timestep
| on_previous_timestep
| ``N`` _timesteps_back
| since_ ``T``
| over_ ``T``
| reset_every_ ``T``

Computational
-------------

Prefixes
^^^^^^^^

| lower_bound_of
| upper_bound_of
| unfiltered
| nonnegative
| is
| do
| identifier_for
| control_for
| number_of
| index_of
| vertical_index_at
| vertical_dimension_of
| cumulative
| iounit_of
| filename_of
| frequency_of
| period_of
| XYZ_dimensioned
| tendency_of ``X``
| generic_tendency
| one_way_coupling_of ``_X`` _to ``_Y``
| tunable_parameter[s]_for ``_X``
| map_of


Infixes
^^^^^^^

| directory_for ``_X`` _source_code

Suffixes
^^^^^^^^

| for_coupling
| for_chemistry_coupling
| from_coupled_process
| from_wave_model
| collection_array
| multiplied_by_timestep
| for_current_mpi_rank
| for_current_cubed_sphere_tile
| plus_one
| minus_one
| for_radiation
| for_deep_convection
| for_microphysics

Transformations
---------------

Prefixes
^^^^^^^^
| change_over_time_in ``_X``
| convergence_of ``_X`` or horizontal_convergence_of ``_X``
| correlation_of ``_X`` _and ``_Y`` [_over ``_Z``]
| cosine_of ``_X``
| covariance_of ``_X`` _and ``_Y`` [_over ``_Z``]
| component_derivative_of ``_X``
| derivative_of ``_X`` _wrt ``_Y``
| direction_of ``_X``
| divergence_of ``_X`` or horizontal_divergence_of ``_X``
| histogram_of ``_X`` [_over ``_Z``]
| integral_of ``_Y`` _wrt ``_X``
| ln ``_X``
| log10 ``_X``
| lwe_thickness_of ``_X``
| magnitude_of ``_X``
| probability_distribution_of ``_X`` [_over ``_Z``]
| probability_density_function_of ``_X`` [_over ``_Z``]
| product_of ``_X`` _and ``_Y``
| ratio_of ``_X`` _to ``_Y``
| reciprocal_of ``_X``
| sine_of ``_X``
| square_of ``_X``
| standard_deviation_of ``_X``
| tendency_of ``_X``
| variance_of ``_X``
| volume_mixing_ratio_of ``_X``

Suffixes
^^^^^^^^
| ``X_`` mixing_ratio_wrt ``_Y``

Other common standard name components
=====================================

Reserved phrase
---------------

These words/phrases should not be used outside of the described context

+------------------------+-------------------------------------------------------------------------------------+
| **Phrase**             |  **Usage**                                                                          |
+========================+=====================================================================================+
| ccpp                   | Variable names provided by the CCPP framework                                       |
+------------------------+-------------------------------------------------------------------------------------+


Special phrases
---------------

+------------------------+-------------------------------------------------------------------------------------+
| **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                                                                                 |
+------------------------+-------------------------------------------------------------------------------------+
| interface              | The vertical boundary of a model layer.                                             |
+------------------------+-------------------------------------------------------------------------------------+
| longwave               | Longwave radiation. Defined as thermal emission of radiation from the planet.       |
+------------------------+-------------------------------------------------------------------------------------+
| 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. Defined as electromagnetic emissions from the sun              |
+------------------------+-------------------------------------------------------------------------------------+
| specific               | per unit mass unless otherwise stated                                               |
+------------------------+-------------------------------------------------------------------------------------+
| unfrozen_water         | liquid and vapor                                                                    |
+------------------------+-------------------------------------------------------------------------------------+
| water                  | water in all phases if not otherwise qualified                                      |
+------------------------+-------------------------------------------------------------------------------------+
| dimensionless          | lacking units                                                                       |
+------------------------+-------------------------------------------------------------------------------------+
| kinematic              | refers to surface fluxes in "native" units (K m s-1 and kg kg-1 m s-1)              |
+------------------------+-------------------------------------------------------------------------------------+
| direct                 | used in radiation (as opposed to diffuse)                                           |
+------------------------+-------------------------------------------------------------------------------------+
| diffuse                | used in radiation (as opposed to direct)                                            |
+------------------------+-------------------------------------------------------------------------------------+

.. _Aliases:

Acronyms, Abbreviations, and Aliases
====================================

+---------------------+---------------------------------------------------------+
| **Short**           |  **Meaning**                                            |
+=====================+=========================================================+
| cnvc90              | GFS Convective Cloud Diagnostics                        |
+---------------------+---------------------------------------------------------+
| edmf                | eddy-diffusivity/mass-flux                              |
+---------------------+---------------------------------------------------------+
| gwd                 | gravity wave drag                                       |
+---------------------+---------------------------------------------------------+
| gfdl                | Geophysical Fluid Dynamics Laboratory                   |
+---------------------+---------------------------------------------------------+
| gfs                 | Global Forecast System                                  |
+---------------------+---------------------------------------------------------+
| ir                  | infrared                                                |
+---------------------+---------------------------------------------------------+
| lwe                 | liquid water equivalent                                 |
+---------------------+---------------------------------------------------------+
| max                 | maximum                                                 |
+---------------------+---------------------------------------------------------+
| min                 | minimum                                                 |
+---------------------+---------------------------------------------------------+
| myj                 | Mellor-Yamada-Janjic scheme                             |
+---------------------+---------------------------------------------------------+
| mynn                | Mellor-Yamada-Nakanishi-Niino scheme                    |
+---------------------+---------------------------------------------------------+
| nir                 | near-infrared part of the EM spectrum (radiation)       |
+---------------------+---------------------------------------------------------+
| nrl                 | Naval Research Lab                                      |
+---------------------+---------------------------------------------------------+
| nsstm               | GFS near-surface sea temperature scheme                 |
+---------------------+---------------------------------------------------------+
| pbl                 | planetary boundary layer                                |
+---------------------+---------------------------------------------------------+
| pdf                 | probability density function                            |
+---------------------+---------------------------------------------------------+
| rrtmgp              | Rapid Radiative Transfer Model for General circulation  |
|                     | model applications - Parallel                           |
+---------------------+---------------------------------------------------------+
| sas                 | simplified Arakawa-Schubert scheme                      |
+---------------------+---------------------------------------------------------+
| skeb                | stochastic kinetic energy backscatter                   |
+---------------------+---------------------------------------------------------+
| shoc                | simplified higher-order closure stochastic scheme       |
+---------------------+---------------------------------------------------------+
| shum                | stochastically perturbed boundary-layer humidity scheme |
+---------------------+---------------------------------------------------------+
| sppt                | stochastically perturbed physics tendencies             |
+---------------------+---------------------------------------------------------+
| stp                 | standard temperature (0 degC) and pressure (101325 Pa)  |
+---------------------+---------------------------------------------------------+
| tke                 | turbulent kinetic energy                                |
+---------------------+---------------------------------------------------------+
| toa                 | top of atmosphere                                       |
+---------------------+---------------------------------------------------------+
| ugwp                | Unified Gravity Wave Physics                            |
+---------------------+---------------------------------------------------------+
| uv                  | ultraviolet part of the EM spectrum (radiation)         |
+---------------------+---------------------------------------------------------+
| vis                 | visible part of the EM spectrum (radiation)             |
+---------------------+---------------------------------------------------------+
| wrt                 | with respect to                                         |
+---------------------+---------------------------------------------------------+

Units
=====

Entries in the Standard Names dictionary contain a "units" property that serves to indicate the
typical/recommended units for a given variable. It is not mandatory to use the indicated units exactly,
but any use of a given standard name variable should have units of the same dimensionality.

When adding a new standard name, units should follow the `International System of Units (SI/metric system) <http://nist.gov/pml/owm/metric-si/si-units>`_.
If the new standard name has an existing match in the `Climate and Forecast (CF) metadata
conventions <https://cfconventions.org/standard-names.html>`_, the units should be identical to the canonical units listed there

For dimensionless variables, the following units can be used:

+------------------------+-----------------------------------------------------------------------------------------------+
| **Unit**               |  **Use case**                                                                                 |
+========================+===============================================================================================+
| count                  | integers that describe the dimension/length of an array                                       |
+------------------------+-----------------------------------------------------------------------------------------------+
| flag                   | logicals/booleans that can be either true or false                                            |
+------------------------+-----------------------------------------------------------------------------------------------+
| index                  | integers that can be an index in an array                                                     |
+------------------------+-----------------------------------------------------------------------------------------------+
| kg kg-1                | mass mixing ratios                                                                            |
+------------------------+-----------------------------------------------------------------------------------------------+
| m3 m-3                 | volume fraction (e.g. for soil moisture)                                                      |
+------------------------+-----------------------------------------------------------------------------------------------+
| mol mol-1              | molar mixing ratios (also volumetric mixing ratio for gases)                                  |
+------------------------+-----------------------------------------------------------------------------------------------+
| none                   | strings and character arrays                                                                  |
+------------------------+-----------------------------------------------------------------------------------------------+
| fraction               | fractions not listed above, typically valid in the range [0,1]                                |
+------------------------+-----------------------------------------------------------------------------------------------+
| percent                | fractions expressed in percent, typically ranging from 0% to 100%                             |
+------------------------+-----------------------------------------------------------------------------------------------+
| 1                      | any number (integer, real, complex) not listed above, e.g. scaling factors, error codes, etc. |
+------------------------+-----------------------------------------------------------------------------------------------+