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- all data and coordinate variables must have a unique variable name and the following attributes:
units (required)
standard_name (required)
long_name (recommended)
_FillValue and/or missing_value (required if there are missing values in the data)
scale_factor (optional to compact data)
add_offset (optional to compact data)
Also see http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#units, http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#long-name and http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#standard-name. - the standard_name attributes should comply to the list with standard names, see http://cfconventions.org/Data/cf-standard-names/26/build/cf-standard-name-table.html.
- a data variable for a 2D grid must depend on three dimensions, representing time and two spatial dimensions (in either the order time, y, x or time, x, y). The names of the dimensions can be anything. For the time dimension there must be a corresponding 1D time coordinate variable with the same name. If the grid is regular or rectangular, then for each spatial dimension there must be a corresponding 1D coordinate variable with the same name. See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#idp5553648. If the grid is curvilinear, then the y and x coordinate variables are both 2D and depend on both spatial dimensions. In this case the data variable must have an attribute "coordinates" that refers to the y and x coordinate variables (in that order), e.g. coordinates="y x". See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#idp5559280. Each coordinate variable must have an attribute "axis" that indicates which axis is defined by that coordinate variable. For the time coordinate variable the axis must be "T", for the x coordinate variable the axis must be "X", for the y coordinate variable the axis must be "Y".
- if the data has a forecast reference time/analysis time/base time, then this time must be stored in a separate coordinate variable that contains only one value, which is the forecast reference time. This variable must have standard_name="forecast_reference_time". The name of this variable must be present in the coordinates attribute of the data variable, e.g. coordinates="analysis_time" or coordinates="y x analysis_time". If needed, different data variables can point to different forecast reference time variables. See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#scalar-coordinate-variables
- the time coordinate variable must have an attribute "units" with a valid unit of time and an attribute "axis" with value "T". A valid unit of time is a string formatted as per the recommendations in the Udunits package, e.g. units="minutes since 1970-01-01 00:00:00.0 +0000". See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#time-coordinate.
- the time and spatial coordinate variables must have values either in ascending or in descending order.
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