CAM-Chem Download

ACOM subset downloads are unstable as of November 25, 2023.

CAM-Chem results for a subset of the globe and a range of dates can be downloaded from this page. Output is provided every 6 hours. Each request is provided as a single netcdf file. We strongly recommend that you download a single day for your region to check the file size and then request a range of dates that will result in a manageable file size. Requests for time spans longer than 32 days are not supported. Questions about CAM-Chem and requests for additional dates can be addressed to Rebecca Buchholz (buchholz at ucar . edu).

Direct data download is also avalailable from the NCAR Research Data Archive; registration is required. If you are retrieving the entire globe, please register and download directly from the NCAR RDA instead.

The 'date' and 'datesec' variables contain the date and time of the CAM-Chem output. To verify the date of the downloaded files, please use 'ncdump -v date'. The program ncview does not properly interpret the 'time' variable and calculates an erroneous date.

CAM-Chem results are available for January 1, 2001 to December 31, 2020. Further details are available at the Wiki page CESM2.1: CAM-Chem as Boundary Conditions. For more recent dates, consider using WACCM forecasts. If you require further information, please contact Rebecca Buchholz (buchholz at ucar . edu).

Please enter your contact information in the space below:

  • E-mail:

November 10, 2020: The personal data (e-mail) that you provide to UCAR/ACOM here is necessary to identify you as a user of CAM-Chem model output and to notify you when your data packet is ready. We also provide update notices by e-mail. The optional personal data provided below will be used to organize discussion forums (example). We do not use your personal data outside of UCAR/ACOM, and we share only non-personal aggregated data for reporting purposes to third parties. For more information about Privacy at UCAR, see UCAR’s Privacy and Cookies Notices.

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  • I allow ACOM to retain my contact information for notification of updates and possible collaboration. If you want us to remove your information later, please let us know.

Enter the lat-lon and date bounds of the region to extract:

To specify a box that crosses the Greenwich Meridian, enter longitude values like: 340 West and 20 East (from 20W to 20E).
North latitude (-90.0 to 90.0):
West longitude (0.0 to 360.0):
East longitude (0.0 to 360.0):
South latitude (-90.0 to 90.0):

Starting date: Ending date:

Submit your data request here:

27600 downloads since 2018-11-29.


To cite the data directly, please use:

Buchholz, R. R., Emmons, L. K., Tilmes, S., & The CESM2 Development Team, (2019). CESM2.1/CAM-chem Instantaneous Output for Boundary Conditions. UCAR/NCAR - Atmospheric Chemistry Observations and Modeling Laboratory. Subset used XXX, Accessed* dd mmm yyyy,

Please fill in the "subset used" with region and/or date of the subset you used (e.g. Lat: -10 to 10, Lon: 100 to 150, September 2015 - February 2016).

*Please fill in the "Accessed" date with the day, month, and year that you last accessed the data (e.g. - 5 Aug 2011).

We suggest to also cite the following paper that discusses the new configuration of CESM2/CAM-chem and assesses chemical species, including using output from this boundary condition simulation.

Emmons, L. K., Schwantes, R. H., Orlando, J. J., Tyndall, G., Kinnison, D., Lamarque, J.‐F., et al., (2020). The Chemistry Mechanism in the Community Earth System Model version 2 (CESM2). Journal of Advances in Modeling Earth Systems, 12, e2019MS001882,