GEOS-Chem Newsletter September 2010

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Dear GEOS-Chem Users,

Here is your September GEOS-Chem Newsletter.

Thank you for your continued support of GEOS-Chem. Happy Equinox!

Bob Yantosca and Claire Carouge

News from the GEOS-Chem Steering Committee

Previous meeting

The last GEOS-Chem Steering Committee telecon took place on September 21st, 2010. We invite you to read the meeting documents listed below:

  1. September 21st Steering Committee Meeting Minutes

Next meeting

The next GEOS-Chem Steering Committee date is TBD (possibly January 4th). We will confirm the date shortly.

If you would like to bring any items to the attention of the Steering Committee before the next telecon, please contact your Working Group Chairperson(s).

GEOS-Chem developer credit

The GEOS-Chem Developer Credit and GEOS-Chem Code Development History web pages have been updated to reflect the latest information from the release of GEOS-Chem v8-03-01. Please visit these pages at your convenience.

Development of the GEOS–Chem model and its adjoint is a grass-roots activity by individual scientists pursuing their own research interests and sharing their work for the benefit of all. Good functioning of the GEOS–Chem community and faster sharing of new model features is promoted by users offering co-authorship for recent developments.

The 5th GEOS-Chem Users' Meeting

The 5th GEOS-Chem Users' Meeting will take place at Harvard University from May 2-5, 2011. SAVE THE DATE!

We will be posting the meeting agenda and travel/lodging information in the upcoming weeks. Please keep checking this web page for more information.

News from the GEOS-Chem Working Groups

Sources and Sinks Working Group

The Emissions Working Group has been renamed to the Sources and Sinks Working Group. This group will be co-chaired by Randall Martin (Dalhousie U.) and Paul Palmer (U. Edinburgh). Please welcome Paul to the GEOS-Chem Steering Committee!

The Sources and Sinks Working Group will address issues pertaining to emissions as well as fluxes to/from the atmosphere (including wet and dry deposition).

Working Groups Overview

We encourage each GEOS-Chem user to join the GEOS-Chem Working Group that is most relevant to his/her area of research. Please see the following working group wiki pages for more information:

  1. Adjoint and Data Assimilation Working Group
  2. Aerosols Working Group
  3. Carbon Gases and Organics Working Group
  4. Hg and POPs Working Group
  5. Oxidants and Chemistry Working Group
  6. Regional Air Quality Working Group
  7. Sources and Sinks Working Group

Each GEOS-Chem user should also post a short description of their project(s) on the relevant Working Group wiki page. Please remove any obsolete projects, add new ones, and review the work planned by other groups. This will allow the Working Group Chairpersons to be informed about the type of research that is being conducted by individual GEOS-Chem users while avoiding duplication of effort.

News from the GEOS-Chem Support Team

Opening for scientific programmer position

Daniel Jacob wrote:

Dear GEOS-Chem user -
Claire Carouge, valued member of the GEOS-Chem support team, is moving to Australia. She will fortunately be able to continue support GC operations for a while remotely but we need to replace her. So -
I am looking to hire a top-notch scientific programmer to support the GEOS-Chem model for the worldwide user community (50%) and operations at Harvard (50%). The ideal candidate for the job would be a PhD scientist with modeling experience and who would like to work in this support position for a while or long-term. Career growth opportunities are excellent.
Please bring this job opportunity to the attention of whoever you think may be interested. Interested candidates, please contact me.
Best wishes with your GEOS-Chem modeling!
Daniel J. Jacob
GEOS-Chem Model Scientist


Claire Carouge will move to Australia by the end of October. She will be able to work remotely from Australia and continue to provide GEOS-Chem support. Bob Yantosca will remain at Harvard and will continue to coordinate all GEOS-Chem support tasks with Claire.

Due to the time difference between Boston and Canberra (14 hours), communication will necessarily take longer. Therefore, this may result in increased turnaround times for GEOS-Chem support requests. We ask for your patience in this regard.

On the other hand...having Claire in Australia also means that we can for the first time bring you round-the-clock GEOS-Chem support! Those of you who live in Asia or Oceania will benefit directly from this!

GEOS-Chem Communications


The GEOS-Chem People and Projects and GEOS-Chem Publications pages have recently been updated.

If you have new paper submissions, please send them to Bob and Claire at


We encourage all GEOS-Chem code developers and users to check the wiki frequently, as this is the place where the latest information about GEOS-Chem will be posted. The wiki is designed to be a two-way street of communication. Users should feel free to add content to the wiki pages that are most closely related to their research.

In particular, the GEOS-Chem Support Team has started a new effort to make sure that all 3rd-party code and data that is submitted into GEOS-Chem has a corresponding wiki page. This will ensure that all information can be shared transparently.

Notable recent updates:

  1. The GEOS-Chem welcome letter for new users has been reorganized to provide a clearer explanation of the expectations and responsibilities of all GEOS-Chem users, as well as how to download the GEOS-Chem source code and data.
  2. A table of recently-released GEOS-Chem versions, release dates, and important features has been added to the GEOS-Chem versions under development page.
  3. A new Dynamic tropopause page has been created. This describes the implementation of the dynamic tropopause in GEOS-Chem. Information about the tropopause diagnostics is also provided here.
  4. The Mercury and Global Terrestrial Mercury Model pages have been updated with the latest information for GEOS-Chem v8-03-02.
  5. A page for GEOS-Chem v9-01-01 has been added.

Email lists

All GEOS-Chem users should sign up for the GEOS-Chem Users email list, as well as one or more of the following Working Group email lists:

  1. GEOS-Chem Adjoint
  2. GEOS-Chem Aerosols
  3. GEOS-Chem Carbon Gases & Organics
  4. GEOS-Chem Hg & POPs
  5. GEOS-Chem Oxidants & Chemistry
  6. GEOS-Chem Regional Air Quality
  7. GEOS-Chem Sources & Sinks

GEOS-Chem development

GEOS-Chem v8-03-02

GEOS-Chem v8-03-02 was released on 07 Sep 2010 and contains the following updates:

  1. Terrestrial and deep ocean mercury (N. Smith-Downey, E. Sunderland)
  2. Updated CO2 simulation (R. Nassar)
  3. Liquid water content taken from GEOS-5 met fields (J. Fisher)

Also, a couple of patches were made after the release of v8-03-02. These patches have been added to the remote GEOS-Chem repository.

Please see our Using Git with GEOS-Chem wiki page for more information about how to download and manage the GEOS-Chem source code.

GEOS-Chem v9-01-01

GEOS-Chem v9-01-01 will be the next version to be released. It will contain the following updates:

  1. Compatibility with MERRA met fields (GEOS-Chem Support Team)
  2. Modified algorithms for convective updraft scavenging and wet deposition (H. Amos, B. Corbitt, Q. Wang et al)
  3. Bug fix: Restore capability to start GEOS-Chem from any arbitrary date & time (GEOS-Chem Support Team)

MERRA reanalysis met fields


The GEOS-Chem Support Team has started the process of modifying GEOS-Chem for use with the MERRA met field product. MERRA is a 30-year reanalysis done with GMAO's GEOS-5.2.0 GCM.

While many aspects of MERRA are similar to the GEOS-5 data product, there are significant differences in certain data fields that require special handling before GEOS-Chem be driven by the MERRA product.

For the latest information, please the following wiki pages:

  1. MERRA
  2. List of MERRA met fields used by GEOS-Chem
  3. MERRA implementation details

Wet scavenging

The MERRA data archive contains several fields which describe the formation of convective and large-scale precipitation, as well as re-evaporation of convective and large-scale condensate. We are modifying our algorithms for wet deposition and wet scavenging in convective updrafts to use this new information from MERRA. The modifications will be added into GEOS-Chem v9-01-01.

Helen Amos, Bess Corbitt, et al have prepared documents which describe these new algorithms. Please see:

  1. Algorithms for wet scavenging in convective updrafts (in convection_mod.f)
  2. Algorithms for wet deposition (in wetscav_mod.f)


Bob Yantosca has prepared a comparison of GEOS-Chem emissions using GEOS-5 and MERRA as a "sanity-check" validation. The findings were:

  1. Emissions that do not depend on the met fields (e.g. anthropogenic, biogenic, biofuels) are not affected by the switch from GEOS-5 to MERRA.
  2. Biogenic emissions (which depend on surface temperature, winds, and PAR) show minor differences between GEOS-5 and MERRA.
  3. Lightning NOx emissions will require a "re-tuning" of the OTD/LIS flash distributions. This can be done once several years of met field data have been processed.
  4. Dust emissions will have to be "re-tuned" by adjusting a parameter in the DEAD dust source function.

Therefore, the "full chemistry" simulation with MERRA will not be ready until #3 and #4 are done. Other offline simulations (e.g. mercury, offline aerosol, black carbon) can be used with MERRA right away.

Data availability

The GEOS-Chem Support Team has started to download and regrid the MERRA data for GEOS-Chem. At present we have downloaded the following time periods.

  • 2008: full year 4° x 5°
  • 2005: full year 4° x 5°
  • 2004: full year 4° x 5°

We plan to obtain the full 30-year MERRA archive (1979-2010). At present, we are only regridding the data to 4° x 5° due to disk storage limitations at Harvard. After a planned storage upgrade we will have the capacity to also store the 2° x 2.5° MERRA data as well.

Nested-grid capability

It is not possible to conduct 0.5° x 0.667° nested-grid simulations with MERRA. This is because the MERRA grid structure differs depending on which quantity you are archiving. Many met fields are stored 1° x 1.25° or 1.25° x 1.25° resolution. Therefore, not all MERRA fields are at the very fine 0.5° x 0.667° grid as they are in GEOS-5.

We may be able to find a way to use the MERRA precipitation fields for GEOS-5 simulations. Lyatt Jaegle will be spearheading that research effort.

In the pipeline

The following updates will be added into GEOS-Chem following the v9-01-01 release.

Item Author(s) Status
APM aerosol microphysics Fangqun Yu APM is being validated with a nested grid simulation for Europe. Currently slated for inclusion after the release of GEOS-Chem v9-01-01.
Bromine chemistry mechanism Justin Parella We have begun the process to bring this into the standard code. Will be included after the release of GEOS-Chem v9-01-01.
Add scavenging by snow Qiaoqiao Wang Slated for inclusion into GEOS-Chem v9-01-01 or later versions.

For a complete list of outstanding code updates, please see our GEOS-Chem model development priorities page.

Column code update

An ESMF Gridded Component has been created which calls the GEOS-Chem column chemistry routines. Some key bugs have now been fixed and work to finalize the interface has begun. Bob is currently testing to make sure that the column chemistry code running within the ESMF environment returns the same output as when driven in a GEOS-Chem test environment. The work is ongoing.

At present, column code development is on the back burner due to the pressing need to modify GEOS-Chem to be driven by the MERRA reanalysis product from GMAO.

--Bob Y. 12:35, 28 September 2010 (EDT)