Initial files

The initial files containing 2D and 3D fields to start the forecast are contained in file that begin with ICM* : ICMGG* are the initial gridpoint files, ICMSH* are the initial spectral fields. ICMCL* is the file containing the climatological forcing fields.

The experiment id is contained the names of the initial files, and it is encoded into the GRIB messages within those files.

Use the 'grib_ls' command to examine the initial files:

grib_ls ICMGGob00INIT
grib_ls ICMSHob00INIT

OpenIFS namelist

The file: fort.4 is the model 'NAMELIST'. It contains a list of variable settings or 'switches' that control what the model does. These variables are grouped into separate fortran namelists.

The model will read this file when it starts up. There are many options to control the model. For more information, it is best and recommended to check the comments in the code.

The wave model, WAM, also has a separate namelist.

OpenIFS experiments

An 'experiment' is created for OpenIFS forecast initial data. An experiment identifier, or 'id', is a 4 character sequence, embedded in the initial data filename and as a GRIB key in the headers of each file. For example, ICMSHg8ddINIT, would be the file for the initial spectral  fields ('SH'), for the experiment labelled 'g8dd'.

An experiment can be a single forecast date or a combination of multiple dates. Each date could be a single forecast or a ensemble of forecasts from a single date. But each experiment will use the same model resolution. For example, an experiment comprising a 5 member ensemble with 5 start dates (say 1st-5h December 2015) would result in 25 separate model forecasts.

Listing the experiment id

The command 'exptid' can be used to check and change the experiment id in the GRIB files.

> exptid ICMSHob00INIT
In file ICMSHob00INIT, values of key experimentVersionNumber are:
ob00

The 'experimentVersionNumber' is the GRIB parameter encoded in the GRIB fields.

This can also be seen using the 'grib_ls' command to list the contents of the file:

> grib_ls -p shortName,typeOfLevel,dataDate,experimentVersionNumber ICMSHob00INIT
ICMSHob00INIT
shortName                typeOfLevel              dataDate                 experimentVersionNumber  
t                        hybrid                   20151101                 ob00                    
t                        hybrid                   20151101                 ob00                    
t                        hybrid                   20151101                 ob00  
.......    

The 'exptid' and 'grib_ls' commands can also be used for multiple files:

troifs0@cca-login3:> exptid ICM*
In file ICMCLob00INIT, values of key experimentVersionNumber are:
0001
In file ICMGGob00INIT, values of key experimentVersionNumber are:
0001
ob00
In file ICMGGob00INIUA, values of key experimentVersionNumber are:
ob00
In file ICMSHob00INIT, values of key experimentVersionNumber are:
ob00

Note that the ICMCL and ICMGG*INIT files both have a experimentVersionNumber key of '0001'. This is used for climatological fields.

Changing the experiment id

All experiments with OpenIFS should use a 4-character experiment id. At ECMWF, these ids are assigned by the system. However, OpenIFS users have the freedom to change the experiment id if they choose to.

A command is available with OpenIFS to change the experiment id in the 'bin' directory of the OpenIFS distribution.

> exptid -n ob01 ICM*ob00*
Changing expid from 'ob00' to 'ob01' for ICMCLob00INIT and writing to new file ICMCLob01INIT.
Changing expid from 'ob00' to 'ob01' for ICMGGob00INIT and writing to new file ICMGGob01INIT.
Changing expid from 'ob00' to 'ob01' for ICMGGob00INIUA and writing to new file ICMGGob01INIUA.
Changing expid from 'ob00' to 'ob01' for ICMSHob00INIT and writing to new file ICMSHob01INIT.