Frequently asked questions about GEOS-Chem

On this page we shall answer some commonly asked questions about GEOS-Chem.

Basic information about GEOS-Chem

For new users

• I am a GEOS-Chem new user. What is expected of me?
• On what types of machines can I run GEOS-Chem?
• What kind of simulations can I run with GEOS-Chem?
• What is the horizontal resolution and vertical resolution of GEOS-Chem?
• Which meteorological data fields can be used by GEOS-Chem?
• To whom can I direct GEOS-Chem-related questions?
• What does the GEOS-Chem Steering Committee do?
• What do the GEOS-Chem Working Groups do?

Chemistry mechanisms

Where can I find information about ...

• the Standard chemistry mechanism in GEOS-Chem?
• the Dicarbonyls mechanism in GEOS-Chem?
• the Caltech isoprene mechanism as implemented in GEOS-Chem?
• the bromine chemistry mechanism in GEOS-Chem?
• the KPP chemical solver?
• the Linoz stratospheric ozone chemistry scheme?

Technical questions

• How do I download the GEOS-Chem source code and run directories?
• How do I download the GEOS-Chem data directories?
• What should I do when I encounter an error while running GEOS-Chem?
• Do you have any information about GEOS-Chem performance and GEOS-Chem Scalability?
• Is there a comprehensive list of GEOS-Chem bugs and how they were fixed?
• I am new to programming. Do you have any online resources or tutorials?
• Is there a recommended programming style that I should use?
• Are there any numerical issues or machine-dependent issues that I should be aware of?

Specific questions

Can I run two GEOS-Chem jobs simultaneously?

Timmy Francis wrote:

I would like to know if I can run more than one executables (.geos) by renaming them as .geos1, .geos2 etc. For example using the same restart file, I want to run two simulations, one 'with chemistry' and the other 'without chemistry' after make and rename the executables to geos1 and geos2 and run these in two terminals. Will they interfere with each other and affect the result?

Bob Yantosca replied:

I recommend creating separate run directories for each executable. You can place the identical restart file and input files into each run directory. Then in one run directory you can turn on chemistry in input.geos, and then in the other run directory, you turn off chemistry in input.geos. If you run the GEOS-Chem executables in two separate directories, you will ensure that one executable will not overwrite the files that the other executable creates.

In theory, you should be able to run two simultaneous GEOS-Chem executables in two separate run directories. However, I don't know much about your particular machine. You might find that there is not enough memory to run two simulations at the same time. That is not a problem with GEOS-Chem, but with your system (and is something that the GEOS-Chem Support Team wouldn't be able to help you with).

I would recommend talking with your local IT department to find out how much memory etc. is available to you, and if you would be able to run two simulations at the same time. I think a 4x5 full chemistry simulation takes 2-3 GB of memory, and a 2x2.5 simulation can take up to 8GB of memory.

--Bob Y. 16:58, 3 November 2010 (EDT)