There are currently two possible ways to create reference files for atmospheric nudging 1) by interpolating ECMWF re-analysis data or 2) by storing the atsmopheric field of an continous EC-Earth simulation.

1) Generating nudging files at ECMWF can be done using the same procedure that is required to generate initial conditios Generating atmospheric initial conditions for IFS at ECMWF. However instead of defining a list of dates a 6-hourly output has to be defined in INIBY in prepIFS. The range of the output INIBEGINDATE and INIENDDATE can not exceed one year (or just little more) because the list of dates gets too long.

2) Since only jobs generating one year can be launched the generation of nudging files can take a very long time. There is therefore a way to paralellize the dates using a script that introduces additional loops in prepIFS branch.