Forecast Reference Time

[mo-marqh]

Requirement:

• Output files from LFRic define the forecast_reference_time for the forecast
  • https://vocab.nerc.ac.uk/standard_name/forecast_reference_time/

This is complementary to the time coordinate, which is output from the model (noting #423)

For a single forecast, the definition of a scalar value of forecast_reference_time and a coordinate of time enables the forecast_period to be unambiguously derived from output data.

Out of scope:

• It is not intended to provide an explicit forecast_period coordinate. This is in part due to its derivability and in part due to technical limitations in XIOS that make this challenging to output from the simulation.

[mo-marqh]

An implementation of this functionality was developed within #90 but this implementation had issues which were not resolved within that work.

#90 was superseded by #509, an implementation which provided some of the infrastructure which will allow for the creation of forecast_reference_time (the core functionality was needed for other reasons, so was adopted without frt)

A revised implementation for forecast reference time provision is required, which will need some adaptions to management of elements within the XIOS control configurations, including enforcing unique id within scope.

Constraint:

• There is a limitation in XIOS which limits the ability to write CF compliant date metadata for a forecast_reference_time scalar.

There is development work to provide feature enhancement in XIOS3 but this is not complete:

• https://gitlab.in2p3.fr/ipsl/projets/xios-projects/xios/-/work_items/3