Execute a dry-run simulation

Follow the steps below to perform a GEOS-Chem Classic dry-run simulation:

Complete preliminary setup

Make sure that you have done the following steps;

  1. Downloaded GEOS-Chem Classic source code

  2. Compiled the source code

  3. Configured your simulation

Then doublecheck these settings in the following configuration files:

geoschem_config.yml

  1. start_date: Set the start date and time for your simulation.

  2. end_date: Set the end date and time for your simulation.

  3. met_field: Check if the meteorology setting (GEOS-FP, GEOS-IT, MERRA2, GCAP2) is correct for your simulation.

    Attention

    The convection scheme used to generate archived GEOS-FP meteorology files changed from RAS to Grell-Freitas starting 01 June 2020 with impact on vertical transport. Discussion and analysis of the impact is available at https://github.com/geoschem/geos-chem/issues/1409.

    To fix this issue, different GEOS-Chem convection schemes are called based on simulation start time. This ensures comparability in GEOS-Chem runs using GEOS-FP fields generated using the RAS convection scheme and fields generated using Grell-Freitas, but only if the simulation does not cross the 01 June 2020 boundary. We therefore recommend splitting up GEOS-FP runs in time such that a single simulation does not span this date. For example, configure one run to end on 01 June 2020 and then use its output restart to start another run on 01 June 2020.. Alternatively consider using MERRA2 which was entirely generated with RAS, or GEOS-IT which was entirely generated with Grell-Freitas. If you wish to use a GEOS-FP meteorology year different from your simulation year please create a GEOS-Chem GitHub issue for assistance to avoid accidentally using zero convective precipitation flux.

  4. root_data_dir: Make sure that the path to ExtData is correct.

HISTORY.rc

  1. Set the frequency and duration for each diagnostic collection to be consistent with the settings in geoschem_config.yml.

HEMCO_Config.rc

  1. Check the Settings section to make sure that diagnostic frequency DiagnFreq: is set to the interval that you wish (e.g. Monthly, Daily, YYYYMMDD hhmmss, etc).

  2. Check the Extension Settings section, to make sure all of the required emissions inventories and data sets for your simulation have been switched on.

    Tip

    You can reduce the amount of data that needs to be downloaded for your simulation by turning off inventories that you don’t need.

Run the executable with the --dryrun flag

Run the GEOS-Chem Classic executable file at the command line with the --dryrun command-line argument as shown below:

$ ./gcclassic --dryrun | tee log.dryrun

The tee command will send the output of the dryrun to the screen as well as to a file named log.dryrun.

The log.dryrun file will look somewhat like a regular GEOS-Chem log file but will also contain a list of data files and whether each file was found on disk or not. This information will be used by the download_data.py script in the next step.

You may use whatever name you like for the dry-run output log file (but we prefer log.dryrun). You will need this file to download data (see the next chapter).