Source code repositories
The GEOS-Chem Classic source code is distributed into several GitHub repositories (aka “repos”), as described below. This setup allows the GEOS-Chem core science routines to be easily integrated into several modeling contexts, such as:
GEOS-Chem Classic
GCHP
GEOS-Chem within the NASA/GEOS ESM
GEOS-Chem within CESM
GEOS-Chem withn WRF (aka WRF-GC)
This repository setup also aligns with our GEOS-Chem Vision and Mission statements.
GEOS-Chem repositories
The bulk of the GEOS-Chem Classic code is contained in three repositories:
GEOS-Chem “Science Codebase”
The GEOS-Chem "Science Codebase" repository (https://github.com/geoschem/geos-chem) contains the GEOS-Chem science routines, plus:
Scripts to create GEOS-Chem run directories, plus template configuration files for all simulations;
Scripts to create GEOS-Chem integration tests;
Interfaces (i.e. the driver programs) for GEOS-Chem Classic, GCHP, etc.
HEMCO
The HEMCO repository (https://github.com/geoschem/HEMCO) contains the source code for the Harmonized Emissions Component, which is used to read and regrid emissions, met fields, and other inputs to GEOS-Chem.
GCClassic
The GCClassic repository (https://github.com/geoschem/GCClassic) is a lightweight wrapper that encompasses GEOS-Chem and HEMCO. We say that GCClassic is the superproject (i.e. top-level source code folder), and that GEOS-Chem (science codebase) and HEMCO are submodules.
Other code packages used by GEOS-Chem
GEOS-Chem uses a few code packages that are maintained separately. These are inlined to GEOS-Chem as Git submodules.
Cloud-J
The Cloud-J repository (https://github.com/geoschem/Cloud-J) contains the source code for the Cloud-J photolysis package. This is used to compute reaction rates for photo-dissociation reactions in the GEOS-Chem fullchem and Hg chemistry mechanisms.
Reference: Prather [2015]
ISORROPIA/HETP
The ISORROPIA/HETP repository (https://github.com/geoschem/HETerogeneous-vectorized-or-Parallel) contains the source code for HETP, which is an implementation of the ISORROPIA II aerosol thermodynamics scheme written in modern Fortran.
Reference: Miller et al. [2024]