This page describes how OpenIFS/AC v1 (derived from OpenIFS 43r3v2) can be obtained, built and used for forecast experiments. The documentation shows examples of how to use the model on the ECMWF Atos Sequana XH2000 HPCF (hpc2020). Adjustments will need to be made for local installations. 

1. OpenIFS/AC compared to the standard OpenIFS model

OpenIFS/AC consists of the standard OpenIFS model and the additional composition software package. Both components together are referred to as OpenIFS/AC (with AC standing for "atmospheric composition"). 

The standard OpenIFS model is described in detail in the OpenIFS 43r3 User Guide. The user guide introduces the model's components and supported model grids. It informs about additional required software packages and how to build the OpenIFS model. It further describes how to carry out an acceptance test after a successful model build in order to verify the model's functionality.

1.1. Additional model sources

In the standard OpenIFS model the source code for atmospheric composition (atmospheric chemistry and aerosol code) has been replaced by dummy routines. The additional model sources for OpenIFS/AC replace these dummy routines and substitute the full composition source code. It is therefore necessary to rebuild the binary model executable after adding the additional model source code. This process is described further below.

1.2. Additional data packages

In order to run OpenIFS with atmospheric composition a substantial number of additional input data files are required. These provide initial conditions for the chemical and aerosol fields as well as additional boundary conditions for the model, mostly in the form of emission fluxes for a number of chemical tracers. These emissions are released mostly at the model surface, however they can also be associated with emission heights (e.g. for engine emissions from global air traffic). Further information is required for the physical removal of tracers through either wet scavenging or dry deposition, the latter of which is related to the surface vegetation type. 

The additional data packages required for atmospheric composition modelling need to be prepared for the model at the desired grid resolution. While the standard OpenIFS model can be used with a wide range of model grids, the prepared chemical input data is only available for few selected grid resolutions and for specific time periods. If the model is to be used for other time periods or at different horizontal or vertical grid resolutions then the additional data packages need first to be generated for this purpose. 

2. Obtaining the model code

This section contains information about where the source code package for OpenIFS/AC can be obtained and how the sources should be installed.

2.1. Working with the ftp server

You need to connect to the ECMWF ftp server to download the source package for OpenIFS/AC.  If your institution has signed the OpenIFS license agreement then you can request the ftp password by emailing openifs-support@ecmwf.int.

You can either convert your existing OpenIFS installation or create a new installation for OpenIFS/AC.  We recommend to create a new installation and for this you will also need the sources of the standard OpenIFS model (oifs43r3v2) which can also be found on the ftp server. 

How to establish a connection to the ECMWF ftp server and how to obtain OpenIFS 43r3 sources is described in more detail here in the OpenIFS User Guide.

ftp ftp.ecmwf.int
(login with username and password for OpenIFS users)
cd src/openifs-ac
get openifs-ac.43r3.v1.gz
bye

2.2. Installing the OpenIFS/AC sources

Installing the model sources and building the model (including acceptance tests) requires approximately 3-4 GB of disk space. The additionally required climatological data packages are not yet included; their installation is described below and will require further disk space.  

Method 1:  We recommend to create a new installation for OpenIFS/AC. This will preserve your original OpenIFS installation and will allow you to use the standard (meteorological) model and the atmospheric composition model interchangeably. 

To proceed you should: 

• Create a new home for the OpenIFS/AC installation. Here we call this location /home/openifs-ac. 
• Change into your new directory and unpack therein the original OpenIFS model sources:   tar xvzf oifs43r3v2.tgz
• In a second step, in the same folder gunzip the OpenIFS/AC sources and patch the original OpenIFS:
  
  • gunzip openifs-ac.43r3.v1.gz
  • patch -p1 <openifs-ac.43r3.v1

Method 2:  Alternatively, in order to convert the standard OpenIFS model to OpenIFS/AC the additional software package for composition needs to be installed into an existing OpenIFS installation. You can create separate binary executables, with and without chemistry enabled. We recommend to create first a backup of your original installation before proceeding.

For the conversion you should:

• Change into your $OIFS_HOME directory where OpenIFS is installed:  cd $OIFS_HOME
• In this directory extract the downloaded source package:
  • gunzip openifs-ac.43r3.v1.gz
  • patch -p1 <openifs-ac.43r3.v1

2.3. Obtaining additional data packages

In addition to the enhancements of the model sources, OpenIFS/AC also requires additional external data to carry out forecast experiments (e.g. climatological data for boundary conditions, fluxes for emitted chemical compounds, etc). This data will complement the data found usually in the $OIFS_DATA_DIR location. The data volume for the standard distribution of OpenIFS/AC is approximately 21 GB. 

As a next step you should: 

• Create a new directory which will contain the additional data that is required for atmospheric composition modelling and it will also contain the new OIFS_DATA_DIR.  Here we call this location /data/openifs-ac. 

• Download the required four additional data tgz archives into /data/openifs-ac.  The following commands will work on the Atos HPC:

  cd /data/openifs-ac
  module load ecfs
  ecp ec:/nm6/oifs/oifs-ac-43r3-chem.tgz .  
  ecp ec:/nm6/oifs/oifs-ac-43r3-xtra.tgz .
  ecp ec:/nm6/oifs/oifs-ac-43r3-initcond.tgz .
  ecp ec:/nm6/oifs/ICMCL-2010.tgz .

• Unpack oifs-ac-43r3-chem.tgz and oifs-ac-43r3-xtra.tgz into /data/openifs-ac. This will result in the following directory structure inside /data/openifs-ac : 

  43r3/chemistry	AC specific
  43r3/xdata	AC specific
  43r3/rtables	Standard dataset for OpenIFS 43r3
  43r3/climate.v015	Standard dataset for OpenIFS 43r3 + AC specifics
  43r3/ifsdata	Standard dataset for OpenIFS 43r3
  43r3/wam	Wave model data for OpenIFS 43r3, needs to be added explicitly

The following two tgz archives can be unpacked to any location, however in this example the files we will also extract them into /data/openifs-ac:

• Unpack oifs-ac-43r3-initcond.tgz into /data/openifs-ac which results in a directory /data/openifs-ac/INITIAL-CONDITIONS.
  The files therein are initial data files for the first day of month for all 12 months of 2010.
• Unpack ICMCL-2010.tgz into /data/openifs-ac which results in a directory /data/openifs-ac/ICMCL.
  This directory contains monthly files with surface boundary conditions (e.g. SSTs, soil temps, albedos, LAI etc).
• In the tgz archives above, the data for the year 2013, provided on a Tl255L60 grid, is required for the T21 acceptance tests. The data for year 2010 is provided on a Tl255L91 grid and can be used for the example forecasts. 
• From your conventional OpenIFS installation's OIFS_DATA_DIR copy the directories ifsdata and rtables to /data/openifs-ac/43r3 as they are also needed here. If this is your first model installation, these data directories are also available from the ftp server. 
• Further, create a directory /data/openifs-ac/43r3/wam which needs to contain wave model initial data for 2010-01-01. 

3. Building the model

This section describes how to build the binary model executable for OpenIFS/AC. Most problems related to building the model executable are due to incorrect environment settings. Therefore we recommend that particular care should be given to the environment settings to ensure that they match the local hardware platform. 

3.1. Environment settings

Similar to the standard OpenIFS model, OpenIFS/AC requires system and user software libraries (e.g. eccodes, netcdf, etc) and relies on shell environment variables which need to be set according to your local installation. In order to avoid the duplication of documentation we refer to the OpenIFS User Guide as the prerequisites for OpenIFS are also valid for OpenIFS/AC.  For more information about environment variable settings please see here. 

In order to build OpenIFS/AC the standard environment settings for oifs43r3v2 can be used with the application of two changes:

• Change $OIFS_HOME to point to your installation of openifs-ac (and not to the standard oifs43r3 installation), in our example this is /home/openifs-ac.
• Change $OIFS_DATA_DIR to the location with the additional data packages, in our example this is /data/openifs-ac.
• Before compiling the model sources edit $OIFS_HOME/make/oifs.fcm to enable chemistry (which is by default disabled).

It is recommend to apply the first two changes in $OIFS_HOME/oifs-config.editme.sh and to activate the settings with the command:  source ./oifs-config.editme.sh  before attempting to build the model. 

In order to run OpenIFS/AC a number of further changes and additions to the environment are required. These are described below.  

3.2. Building the binary executable

On the ECMWF HPCF it is possible to compile the model using a login node. However, in order to complete the acceptance testing with chemistry an interactive node should be requested.

% ecinteractive -c 12 -m 32GB -t 06:00:00

If you have a configuration script that sets the appropriate environment for OpenIFS you should run this first before building the model executables. 

In your command line you should type

export OIFS_CHEM=enable

to overwrite the default setting in oifs.fcm (or alternatively you can edit the variable in file oifs.fcm)

Further you should make a choice whether you want to build with XIOS server support, in that case set appropriate environment variables. Otherwise set   

export OIFS_XIOS=disable

to disable XIOS. 

Then compile the model using fcm (here with verbose output and with 16 parallel child processes):

cd $OIFS_HOME/make
fcm make -v -j 16 -f oifs.fcm

You should only proceed further after the code has compiled and all the executables were built without errors.

4. Running the acceptance tests

The model package offers various tests to check the basic functionality of the model and to verify that all paths to the data directories are correct and accessible.

4.1. Overview

The acceptance tests are run on a T21 full Gaussian grid and are designed to require a minimum of computational resources. Several different tests are being offered which activate different pathways in the model source code. It is highly recommended to carry out these brief tests to verify that the model is working normally prior to using the model for forecast experiments.

The tests are located in $OIFS_HOME/t21test and t21test_xios_t255ac.

Running the tests for the first time requires editing the wrapper scripts job.sh and setup-exp.sh by setting the path to the appropriate master.exe and by changing RUNCMD to to something appropriate for the platform.

t21test:  This directory contains the original acceptance test which is provided with OpenIFS.  It should work in the same way for OpenIFS/AC as described in the OpenIFS User Guide.

t21test_xios:  This directory contains an OpenIFS acceptance test which makes use of the XIOS server – we do not describe this here.

t21test_xios_t255ac:  This directory contains the new tests for OpenIFS/AC. The test consists of a short 1-day run to demonstrate the working of OpenIFS/AC. It has a very limited set of options. Note that you cannot increase the runtime of the experiment because the provided ICMCL file does not contain data for an extended model run. The three acceptance tests in this directory make use of the additional compositon (AC) code and it is possible to run this test (a) without AC as in t21test, (b) with additional AC included, and (c) for both of the previous tests additionally XIOS server output can be selected.

4.2. Step-by-step

Here we describe the required steps to carry out the tests.

4.2.1. Using t21test

./job.sh -n 12 -t 2 -m ../make/gnu-opt-chem-fftw/oifs/bin/master.exe

If the oifs_run script (or the oiac_run script) is used without the --nomove option it produces an error at the end of the acceptance test, stating the ICMGGepc8+* files cannot be found. This refers to the copying of model output to output1 and the postprocessing and is therefore not relevant to the model functionality.

Test result:  This test runs in directory $OIFS_HOME/t21test and model output is written into subfolder output1. The model run also produces the file res_021_0072 which contains results from the error calculation. This error should be below 5%. For more information see the OpenIFS User Guide.

4.2.2. Using t21test_xios_t255ac

Without chemistry:  This test uses a different script compared to the standard OpenIFS model's t21test. First we will verify its correct functionality by running the test without activating the model chemistry.

• To do this we run the standard t21test for experiment epc8 (T21L19) with the setup-exp.sh new script.
• The name for the hardware platform needs to be set (l.89, e.g. platform=ecmwf-hpc2020)
• The test experiment runs in the RUNDIR directory specified in setup-exp.sh (l.94, the default is $SCRATCH/43r3/epc8/).
• We also need to use the command line option -x and give as argument the absolute full path to the master.exe binary executable.
• In setup-exp.sh you should change the value for RUN_NUMBER otherwise any pre-existing model output from this test will be overwritten. 

./setup-exp.sh -n 16 -t 2 -x /home/damk/oifs/model/openifs-ac/make/gnu-opt-chem-fftw/oifs/bin/master.exe

Test result:  As before an error calculation file res_021_0072 is created in the run directory and the model output is found in the subfolder output1 (this name depends on the RUN_NUMBER variable). 

With chemistry:  Now repeat the test with enabled model chemistry. This is a short 1-day test run that uses the newly added source code of OpenIFS/AC. It has a very limited set of options and should not be used for forecast experiments. Note that you cannot increase the experiment duration beyond one day because the boundary conditions are only supplied from 2013-07-01 to 2013-07-03. 

This experiment is named oiac and uses a Tl255L60 grid and runs for 24 hours. The default run directory is $SCRATCH/43r3/oiac/. 

./setup-exp.sh -c -n 16 -t 2 -x /home/damk/oifs/model/openifs-ac/make/gnu-opt-chem-fftw/oifs/bin/master.exe

This test runs with a 30 min time step and due to the computational requirements for the added chemistry it will take much longer to complete. The variable CHEM_SCHEME offers the choice of two chemistry schemes, the AER aerosol scheme is always enabled. 

Test result:  This experiment calculates budgets of atmospheric mass, along with overall production and loss tendencies, as well as more detailed reaction budget terms relevant for the ozone production and loss tendency. These are printed in the NODE.001_01 file and afterwards extracted to the files $RUNDIR/output{$RUN_NUMBER}/massdia_chem_oiac.txt and ozonbud_chem_dia.txt.

These diagnostics can be compared with pre-calculated results in files massdia_chem__oiac_2013070100.txt and ozonbud_chem__oiac_2013070100.txt which are located in $OIFS_HOME/t21test_xois_t255ac/ctrl/. For example this could be done with a small shell script such as illustrated in the box below. 

EXPID=oiac; RUNDIR=${SCRATCH}/${OIFS_CYCLE}/${EXPID} ;  RUN_NUMBER=3  #checkoifs
fref1=${OIFS_HOME}/t21test_xios_ac/ctrl/massdia_chem__oiac_2013070100.txt
fref2=${OIFS_HOME}/t21test_xios_ac/ctrl/ozonbud_chem__oiac_2013070100.txt
fnew1=${RUNDIR}/output${RUN_NUMBER}/massdia_chem_oiac.txt
fnew2=${RUNDIR}/output${RUN_NUMBER}/ozonbud_chem_oiac.txt
diff $fref1 $fnew1
diff $fref2 $fnew2

As a rule of thumb, differences between the reference budget numbers and those from the t21test should be only small (below 5%), although this depends on the exact variable that is assessed. 

5. Single forecast experiments

This section describes the required steps to carry out a single forecast experiment (no restarts) with chemistry. The essential three steps can be summarised as:

1. Edit paths and variables in $OIFS_HOME/AC-experiments/config.h. This controls model switches and the chemistry scheme. 
2. Prepare initial conditions using $OIFS_HOME/AC-epxeriments/prep-ic-icmcl-compo.sh.
3. Customise a job wrapper script for the relevant hardware platform (a *.job file) in order to submit the oifs-run.sh script to the batch scheduler.

5.1. Overview of the AC-experiments directory

AC-experiments/
├── config.h                   # MAIN experiment config file
├── ctrl/
│   ├── context_ifs.xml        # xios resource
│   ├── ifs_xml/               # xios resource
│   ├── iodef.xml              # xios resource
│   ├── namelistfc 
│   ├── namelist.ifs-epc8.sh   # namelist for t21test without chemistry
│   ├── namelist.ifs-oiac.sh   # namelist for t21test with chemistry
│   ├── namelist.ifs.sh        # namelist template for forecast experiments
│   ├── Table/                 # dir with AC tracers
│   └── wam_namelist
├── ecmwf-hpc2020.job          # job wrapper script for oifs-run.sh
├── oifs-run.sh                # MAIN run script
├── platform/                  # dir with platform-specific templates
├── prep_emis/                 # dir with emission utilities
├── prep-ic-icmcl-compo.sh     # MAIN script to prepare initial/boundary conditions
└── scripts/                   # dir with low-level scripts
    ├── add_nrt_fire_chem
    ├── gaussgr
    ├── get_alb_lai_intLimits
    ├── get_tablecol
    ├── grib_def.h
    ├── lib_chem_setup.sh
    ├── lib_general.sh           # lib of utilities
    ├── lib_icmcl_clima.sh       # lib of functs to create ICMCL boundary cond. files
    ├── lib_icmcl_compo.sh       # lib of functs to create ICMCL-COMPO files
    ├── lib_initcond_offline.sh
    └── lib_initcond.sh          # lib of functs to create initial conditions files

The experiment controls are in $OIFS_HOME/AC-experiments/. 

There the following essential files can be found:

• prep-ic-icmcl-compo.sh  - a script to generate initial conditions for chemical fields for the selected run time. Begin and end date need to be given as an argument.
• config.h  - settings for model installation, paths, and experiment configuration.
• oifs-run.sh  - this script controls the workflow for the experiment: reads experiment config, sets up run directories (in $SCRATCH), loads platform configuration, edits namelists, links to initial conditions and executes OIFS_RUNCMD
• ecmwf-hpc2020.job  wrapper script for oifs-run.sh, required settings for the batch scheduler

In $OIFS_HOME/AC-experiments/platform:

• it is necessary to create a platform-specific machine config file:  oifs-config.ecmwf-hpc2020.sh

The above ecmwf-hpcs2020.job wrapper script to submit the batch job is based on templates in the platform directory; a number of templates exist and for the ECMWF HPCF the following templates are relevant:

• ecmwf-hpc2020.job.tmpl    –    run oifs without XIOS
• oifs-config.ecmwf-hpc2020.sh  –  template for the machine config file

5.2. Editing the experiment configuration file

For the forecast experiment to succeed and in order to generate the initial data correctly, you will need to edit variables inside the file config.h to correspond with the chosen settings for your experiment.

In config.h you should edit the following variables. The example is for a single forecast (without restarts or multiple forecast legs), starting from 1st January 2010 having 48 hours duration. 

PLATFORM='ecmwf-hpc2020' # this needs to match the name of the platform configuration file
EXP=abcd                 # you should select here an experiment ID (4-letter alphanumeric word, must not start with '0')

RUNDIR=${SCRATCH}/43r3/experiments/${EXP}/runs         # this is the experiment directory
AC_IC_DIR=${SCRATCH}/43r3/experiments/${EXP}/chem_ic   # this is the staging directory for initial and boundary conditions data files

# Simulation start and end date. If setting time (not mandatory), **put it before** the date
run_start_date="00:00 2010-01-01"
run_end_date="${run_start_date} + 2 days"
 
rst_freq='6 day'        # Run for 6 days without restarts. Our experiment will finish after 2 days, so this will be ignored. 
USE_RESTART=false       # Do not write restart files.

Path variables need to be set to the appropriate locations. In our example described in the Section above these locations can be found in the OIFS_DATA_DIR under /data/openifs-ac.

OIFS_INIDATA_DIR=${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-tm5-aer   # initial and boundary conditions for the chemistry scheme
ICMCLDIR=${OIFS_DATA_DIR}/ICMCL                                        # physical/meteorological boundary conditions
MET_IC_DIR=${OIFS_DATA_DIR}/ICMCL/aabg/2010010100                      # path for meteorological initial data in case it needs to be generated
AC_IC_ONCE=${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-tm5-aer/ICMUAoiac.ac_rst    # initial conditions for chemical tracers

Further variables and settings that need changing in config.h are described below in the next section for four possible forecast experiment configurations.

Once all the changes have been made in config.h, the experiment initial and boundary condition files can be prepared as described in the following section. 

After the data has been prepared the platform-specific job wrapper script can be executed to submit the model experiment job to the batch scheduler.

5.2.1. Example configuration settings for single forecast experiments

Select one of the following four T255L91 forecast configurations for your experiment.  The tested and supported configurations are:

5.2.2. Using TM5 chemistry without aerosol

Example:  Run a 2-day forecast starting from 2010-01-01 with TM5 chemistry without aerosol.

Use the following settings in config.h:

PLATFORM='ecmwf-hpc2020'

RUNDIR='${SCRATCH}/43r3/experiments/${EXP}/runs'        # where your experiment will run
AC_IC_DIR='${SCRATCH}/43r3/experiments/${EXP}/chem_ic'  # where your chemical initial conditions will be created
run_end_date="2010-01-03"
rst_freq='6 day'
USE_RESTART=false

LCHEM=true
CHEM_SCHEME="tm5"
CHEM_VER="ver15"
OIFS_INIDATA_DIR='${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-tm5-none'

LAERO=false
LAERCHEM=false
LCHEM_AEROI=false
LINJ_CHEM=false
LINJ_AER=false
LAEROSFC=false

LWAM=true
LRLXG=false

5.2.3. Using TM5 chemistry with AER aerosol

Example:  Run a 2-day forecast starting from 2010-01-01 with TM5 chemistry and the AER bulk aerosol scheme.

Use the following settings in config.h:

PLATFORM='ecmwf-hpc2020'

RUNDIR='${SCRATCH}/43r3/experiments/${EXP}/runs'        # where your experiment will run
AC_IC_DIR='${SCRATCH}/43r3/experiments/${EXP}/chem_ic'  # where your chemical initial conditions will be created
run_end_date="2010-01-03"
rst_freq='6 day'
USE_RESTART=false

LCHEM=true
CHEM_SCHEME="tm5"
CHEM_VER="ver15"
OIFS_INIDATA_DIR='${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-tm5-aer'

LAERO=true
LAERCHEM=true
LCHEM_AEROI=true
LINJ_CHEM=true
LINJ_AER=true
LAEROSFC=true

LWAM=true
LRLXG=false

5.2.4. Using BASCOE-TM5 chemistry without aerosol

Example:  Run a-2 day forecast starting from 2010-01-01 with combined BASCOE and TM5 chemistry without aerosol.

Use the following settings in config.h:

PLATFORM='ecmwf-hpc2020'

RUNDIR='${SCRATCH}/43r3/experiments/${EXP}/runs'        # where your experiment will run
AC_IC_DIR='${SCRATCH}/43r3/experiments/${EXP}/chem_ic'  # where your chemical initial conditions will be created
run_end_date="2010-01-03"
rst_freq='6 day'
USE_RESTART=false

LCHEM=true
CHEM_SCHEME="bascoetm5"
CHEM_VER="ver2f"
OIFS_INIDATA_DIR='${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-bascoetm5-none'

LAERO=false
LAERCHEM=false
LCHEM_AEROI=false
LINJ_CHEM=false
LINJ_AER=false
LAEROSFC=false

LWAM=true
LRLXG=false

5.2.5. Using BASCOE-TM5 chemistry with AER aerosol

Example:  Run a-2 day forecast starting from 2010-01-01 with combined BASCOE and TM5 chemistry without aerosol.

Use the following settings in config.h:

PLATFORM='ecmwf-hpc2020'

RUNDIR='${SCRATCH}/43r3/experiments/${EXP}/runs'        # where your experiment will run
AC_IC_DIR='${SCRATCH}/43r3/experiments/${EXP}/chem_ic'  # where your chemical initial conditions will be created
run_end_date="2010-01-03"
rst_freq='6 day'
USE_RESTART=false

LCHEM=true
CHEM_SCHEME="bascoetm5"
CHEM_VER="ver2f"
OIFS_INIDATA_DIR='${OIFS_DATA_DIR}/INITIAL-CONDITIONS/T255L91-bascoetm5-none'

LAERO=true
LAERCHEM=true
LCHEM_AEROI=true
LINJ_CHEM=true
LINJ_AER=true
LAEROSFC=true

LWAM=true
LRLXG=false

5.3. Generating initial data

Initial conditions for the standard OpenIFS model can be generated using the OpenIFS Data Hub or alternatively they can be requested from the ECMWF OpenIFS support by email openifs-support@ecmwf.int. This provides initial experiment data and surface boundary conditions for the physical/meteorological NWP forecast model.

In order to simulate atmospheric composition with OpenIFS/AC additional initial and boundary conditions are needed. These can be created using the prep-ic-icmcl-compo.sh script. 

The prep-ic-icmcl-compo.sh script (henceforth: prep script) carries out 4 tasks:

• Creates a destination directory $AC_IC_DIR which serves as a staging area for all initial and boundary conditions required for the forecast experiment. Symbolic links will point later from inside the experiment run directory to these files.
• Copies the physical/meteorological initial conditions files that must be specific to the experiment start date from $OIFS_INIDATA_DIR to the new $AC_IC_DIR. If these files cannot be found then an attempt is made to create them from files found in the $MET_IC_DIR directory. 
• Copies the physical boundary conditions file ICMCL{exp}INIT (SSTs, albedos, etc) from $OIFS_INIDATA_DIR to $AC_IC_DIR and if necessary truncate to length of experiment duration. 
• Copies the chemistry initial and boundary conditions file (emission fluxes, deposition velocities) ICMCL-INIT-COMPO from $OIFS_INIDATA_DIR to $AC_IC_DIR. If this file cannot be found it will be created. 

The syntax to run the prep script is:

./prep-ic-icmcl-compo.sh <start_date> <end_date>

with start_date and end_date having the format YYYY-MM-DD.

In the examples above for a 2-day forecast, the syntax should be  ./prep-ic-icmcl-compo.sh 2010-01-01 2010-01-03  to generate the data for 48 hours from 1st January 2010. 

Running the prep script will take a few minutes and will result in new data that will be written to $AC_IC_DIR, by default this location is $SCRATCH/43r3/experiments/{exp}/chem_ic.

This folder serves as a staging area for the initial and boundary conditions data and if the target files in $AC_IC_DIR already exist then they they will not be overwritten. 

5.3.1. Creating initial conditions at the end of an experiment run

When setting  LAC4IC=true an AC-for-IC grib file is created at the end of a run. It is a snapshot of all chemical/atmospheric composition tracers. This file can be used by the pre-processing script (prep script) to create new initial conditions. 

With the AC-for-IC file, initial conditions for a new experiment can be generated which will provide a continuation of the chemical evolution of the tracer fields from the previous experiment. The meteorological fields to complement the initial conditions can originate from an archived experiment or can be generated with the OpenIFS Data Hub. This workflow is desirable when aiming to reinitialise the model integration with an updated weather forecast or analysis data (which does not provide AC tracers).  

In order to restart with atmospheric composition tracers from the AC-for-IC grib file select the following settings in config.h:

• Either leave the variable OIFS_INIDATA_DIR empty, delete it or comment it out.
• Set the variable AC_IC_ONCE to point to the generated AC-for-IC grib file from the previous experiment. This file is typically found in this location in the previous experiment:
  ${RUNDIR}/output/${RUN_NUMBER}/ICMUA${EXP}.ac_rst
  
• Set the variable MET_IC_DIR to the relevant path for the new experiment's initial conditions or modify the "variables to retrieve METEO initial conditions from an archived experiment" section as appropriate.

5.4. Running the forecast experiment

Now the actual forecast experiment can be submitted to the batch scheduler using the platform-specific job wrapper script. Examples for this are found in $OIFS_HOME/AC-experiments/platform. An example template for the ECMWF HPCF Atos Sequana XH2000 is the file ecmwf-hpc2020.job.tmpl. 

The actual forecast experiment will be carried out inside the run directory which is defined in config.h with variable RUNDIR. The default on the ECMWF HPCF is $SCRATCH/43r3/experiments/${exp}/runs/.

Due to the much increased computational requirements for simulating atmospheric composition, forecast experiments are often broken into individual parts (sometimes referred to as "legs"). For each leg a restart of the forecast experiment needs to be carried out. 

Model Output
The oifs-run.sh script for OpenIFS/AC has been designed to be able to cope with restarts or "legs", and the model output from each experiment leg is stored in individual subfolders named by leg number. In the case of a single forecast experiment without restarts the output will be written to $RUNDIR/output/001.

Log files
Log file and experiment-related configuration data (namelist, NODE file, ifs.stat), as well as text files with diagnostic model outuput (e.g. mass and ozone budgets) are copied to $RUNDIR/log/001.

Restart Data
Model data relevant for restarts (not discussed here on this page) will be stored in $RUNDIR/restart/${next_leg_number}.

XIOS output
Files relevant to XIOS server output are stored in $RUNDIR/ifs_xml (not discussed here on this page). 

6. Multiple forecasts with restarts

There are several reasons why a user may wish to restart a forecast experiment. The increase in computational costs for simulating atmospheric composition may require to break a longer forecast experiment into individual sections ("legs"). Also, a restart will allow to initialise the meteorology in the model with data taken from an analysis of the current modelled time. 

Due to the time scales associated with the different chemical processes and the lifetime of chemical tracers with respect to their loss processes, it is often convenient to retain the chemical tracer fields in the model simulation and update only the driving meteorology at the time of the restart. In some applications, the model could even be initialised every single day with an up-to-date meteorological analysis field while the chemical fields are left to evolve.  The previous section described how chemical initial conditions can be created at the end of an experiment run, thus retaining the chemical tracer information from the previous experiment leg. 

We will here provide some examples of the principle steps required for restarting experiments.

Example 1:  Longer experiment with manual stop and restart

The experiment parameters need to be defined by editing config.h. The following settings are used for a 2-month experiment with a stop-and-restart after the first month. This will result in two experiment legs of 1 month duration each.

run_start_date="2010-01-01"
run_end_date="${run_start_date} + 2 months"
rst_freq="1 month"
USE_RESTART=true

The initial conditions for each leg need to be either created or gathered from a prepared repository.

prep-ic-icmcl-compo.sh  2010-01-01 2010-02-01
prep-ic-icmcl-compo.sh  2010-02-01 2010-03-01 

These processes can be run simultaneously. The meteorological fields and initial conditions can be requested from the OpenIFS Data Hub. The wrapper script needs to be submitted for the first experiment leg. Once the experiment has completed, config.h needs to be edited to use the initial experiment data from the date and time when the first leg has stopped. Then the wrapper script for the second month should be submitted.

Example 2: Using a workflow script

The 4 jobs in the previous example, can be all triggered automatically and in a timely fashion with a single script. The  $OIFS_HOME/AC-experiments/platform/<platform-name>-workflow.sh templates provide examples that need to be adjusted for the local hardware and file paths. In this case the config.h file only needs editing once and instead of the batch job wrapper script the workflow script is submitted.