Frequently asked questions about GEOS-Chem

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

Basic information about GEOS-Chem

For new users

Science questions

Where can I find information about ...

Technical questions

Specific questions

How long does a GEOS-Chem job take?

It depends on your particular machine. We have posted several timing results from GEOS-Chem 4° x 5° (1-month benchmark) and 2° x 2.5° (1-year benchmark) simulations.

My GEOS-Chem job seems to be running too slowly. What can I do?

When you compile GEOS-Chem, several [options] can potentially slow down GEOS-Chem.

Also, the following run-time options may also slow down GEOS-Chem:

"Normal" diagnostics
(e.g. saved out to the ctm.bpch file): The more diagnostic quantities you choose to archive, the more memory and disk I/O operations this will require.
"Timeseries" diagnostics (ND48, ND49, ND50, ND51, ND51b)
If you choose to archive many diagnostic quantities at hourly or bi-hourly intervals, then the increased memory and disk I/O usage can slow down GEOS-Chem.

To speed up GEOS-Chem, you can try to reduce the number of diagnostics that you are saving to disk.

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. 15:44, 8 November 2010 (EST)

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