Download the model

The GCHP source code is hosted at https://github.com/geoschem/GCHP. Clone the repository:

gcuser:~$ git clone https://github.com/geoschem/GCHP.git GCHP

The GCHP repository has submodules (other repositories that are nested inside the GCHP repository) that aren’t automatically retrieved when you do git clone. To finish retrieving the GCHP source code, initialize and update the submodules:

gcuser:~$ cd GCHP
gcuser:~/GCHP$ git submodule update --init --recursive

By default, the source code will be on the main branch which is always the last offocial release of GCHP. Checking out the official release is recommended because it is a scientifically-validated version of the code and is easily citable. You can find the list of past and present GCHP releases here. Checkout the release that you want to work with, and update the submodules:

gcuser:~/GCHP$ git checkout 13.3.4
gcuser:~/GCHP$ git submodule update --init --recursive

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Before continuing, it is worth checking that the source code was retrieved correctly. Run git status to check that there are no differences:

gcuser:~/GCHP$ git status
HEAD detached at 13.3.4
nothing to commit, working tree clean
gcuser:~/GCHP$

The output of git status should confirm your GCHP version and that there are no modifications (nothing to commit, and a clean working tree). It also says that you are are in detached HEAD state, meaning you are not in a GCHP git software branch. This is true for all submodules in the model as well. If you wish to use version control to track your changes you must checkout a new branch to work on in the directory you will be developing.