GEOS-Chem v10-01 Online User's Guide
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Appendix 8: Modifications to facilitate High-Performance Computing in GEOS-Chem
GEOS-Chem will form the core of a fully-coupled system that will connect to the NASA GEOS-5/GCM. Before this can happen, the GEOS-Chem standard model must become compliant with the Earth System Model Framework (ESMF). This will allow us to take advantage of Message Passing Interface (MPI) parallelization via ESMF, which has been a long-term goal of the GEOS-Chem development community. MPI parallelization will facilitate GEOS-Chem simulations at extremely fine horizontal resolution, running on hundreds or thousands of CPUs in High-Performance Computing (HPC) environments.
To achieve this coupling between GEOS-Chem and the NASA GEOS-5 GCM, we have introduced the concept of grid-independence. We no longer shall assume a preset horizontal grid, but instead shall allow the GCM to dictate the size of the grid, and how many grid boxes will be processed by each CPU. This lets us to keep the all calls to ESMF library routines completely outside of GEOS-Chem.
We have made it a priority to implement necesary structural changes into GEOS-Chem without disrupting ongoing GEOS-Chem research projects. We have already removed several legacy code routines that prevented GEOS-Chem from connecting to the NASA GCM. We have added new source code instructions into many GEOS-Chem routines, set apart by C-preprocessor switches. Eventually, the new code will replace the old code, but during the transition phase we must keep both new and old code side-by-side.
We describe below the structural changes that we made to facilitate HPC in GEOS-Chem. Please also see our Grid-Independent GEOS-Chem wiki page.
Our initial preparations involved replacing F77-style legacy code with modern F90 code:
A8.2 Construction of the Chemistry Component
Please see the information on this wiki page:
A8.3 Construction of the Emissions Component
Christoph Keller (Harvard) has created a grid-independent Emissions Component that replaces GEOS-Chem emissions functionality. The Harvard-NASA Emissions Component (HEMCO) has been incorporated into GEOS-Chem v10-01. It has allowed us to remove many legacy emission routines from GEOS-Chem. For a complete list, please see our Removal of obsolete modules and files wiki page.
For more information on HEMCO, please see the following links: