Parameter component¶

Every Field carries a parameter component that describes the physical quantity the field represents. The parameter component is accessible via the parameter attribute of a field and is represented by a subclass of ParameterBase.

>>> import earthkit.data as ekd
>>> field = ekd.from_source("sample", "test.grib").to_fieldlist()[0]
>>> field.parameter.variable()
'2t'
>>> field.parameter.units()
K
>>> field.parameter.standard_name()
'2_metre_temperature'

The same information is available through the generic get() interface using the "parameter." prefix:

>>> field.get("parameter.variable")
'2t'
>>> field.get("parameter.units")
K

The parameter component is immutable. Use the set() method (or set() on the field) to derive a modified copy:

>>> new_field = field.set({"parameter.variable": "msl", "parameter.units": "Pa"})
>>> new_field.parameter.variable()
'msl'

Parameter types¶

The appropriate parameter subclass is determined automatically from the data:

Parameter — standard meteorological parameter with a variable name and units.
ChemicalParameter — parameter that also carries a chemical constituent or aerosol type (chem / chem_long_name keys).
OpticalParameter — parameter defined at a specific wavelength (wavelength, wavelength_bounds, wavelength_units keys).
ChemicalOpticalParameter — combines both chemical and optical information.
WaveSpectraParameter — 2-D wave spectra parameter carrying direction and frequency bins (wave_direction* and wave_frequency* keys).

Accessing parameter information¶

All parameter keys are accessible through get() with the "parameter." prefix, and can therefore be used in sel(), order_by(), and metadata().

Key	Description
`parameter.variable`	Parameter variable name as a string (e.g. `"2t"`). Not normalised; taken directly from the source data. For example, for GRIB data, it will be the value of the “shortName” key in the GRIB message.
`parameter.param`	Alias of `parameter.variable`.
`parameter.standard_name`	CF standard name of the parameter variable.
`parameter.long_name`	CF long name of the parameter variable.
`parameter.units`	Units of the parameter as a `Units` object.
`parameter.chem`	Chemical constituent or aerosol type, or `None` for non-chemical parameters.
`parameter.chem_long_name`	Long name of the chemical constituent or aerosol type, or `None`.
`parameter.wavelength`	Central wavelength for optical parameters, or `None`. Accepts an optional `units` argument for conversion.
`parameter.wavelength_bounds`	Wavelength bounds as a 2-tuple for optical parameters, or `None`.
`parameter.wavelength_units`	Units of the wavelength (e.g. nanometres), or `None`.
`parameter.wave_direction`	Wave propagation direction for 2-D wave spectra parameters, or `None`.
`parameter.wave_direction_index`	0-based index of the wave direction bin, or `None`.
`parameter.wave_direction_bounds`	Direction bounds as a 2-tuple, or `None`.
`parameter.wave_direction_units`	Units of the wave direction (e.g. degrees), or `None`.
`parameter.wave_frequency`	Wave frequency for 2-D wave spectra parameters, or `None`.
`parameter.wave_frequency_index`	0-based index of the wave frequency bin, or `None`.
`parameter.wave_frequency_bounds`	Frequency bounds as a 2-tuple, or `None`.
`parameter.wave_frequency_units`	Units of the wave frequency (e.g. 1/s), or `None`.

Parameter component¶

Parameter types¶

Accessing parameter information¶

How-tos¶