The GEOS–Chem model is a global 3-D model of atmospheric composition driven by assimilated meteorological observations from the Goddard Earth Observing System (GEOS) of the NASA Global Modeling Assimilation Office (GMAO).  It is being developed and used by research groups worldwide as a versatile tool for application to a wide range of atmospheric composition problems.  See the list of people and projects and also our management charter. Also see the list of GEOS–Chem publications.

The GEOS data are available from the NASA Global Modeling Assimilation Office as a continuous archive from 1985 to present.  The most recent GEOS–5 product has a horizontal resolution of 0.5° latitude x 0.667° longitude, with 72 levels in the vertical. We have extracted, processed, and transferred to our machines the entire data set from 1985 to present.  We have also adapted GEOS–Chem to run with climate data from the NASA/GISS general circulation model for simulations of atmospheric composition in past and future climates.

All current applications of the GEOS–Chem model use the same standard code maintained by Bob Yantosca and Philippe Le Sager, with the choice between applications being controlled by logical switches.  Updated versions of this standard code are released regularly. Detailed GEOS–Chem on-line documentation is available including a User's Guide.  The code is fully modular and highly parallelized. It is being used on SGI Origin SGI Altix, Alpha, Sun, IBM, and Linux cluster platforms.

An IDL-based Global Atmospheric Modeling (output) Analysis Package (GAMAP) facilitates the visualization of GEOS–Chem model outputs.  GAMAP takes in 5-D model output fields (concentrations in 3-D space, time, tracer #) and through an user-friendly interface allows easy generation of a wide variety of plots and animations.  GAMAP was originally written by Martin Schultz and is being maintained and further developed by Bob Yantosca and Philippe Le Sager.

The GEOS–Chem model also contributes to a number of broader activities in the atmospheric research community. These include:

• Regulatory models for air pollution: GEOS–Chem provides the outer global nest for the Community Multiscale Air Quality (CMAQ) modeling system of the U.S. Environmental Protection Agency. The GEOS–Chem/CMAQ interface was developed by Daewon Byun's group at the University of Houston.

• Community assessment models: GEOS–Chem is a major contributor to the NASA Global Model Initiative (GMI) which incorporates modules from different research CTMs into a flexible modeling framework.

• Climate change: GEOS–Chem has been interfaced with the NASA/GISS general circulation model to investigate the effects of climate change on atmospheric composition. This work is part of the multi-institutional Global Change and Air Pollution (GCAP) project.

• Chemical data assimilation: GEOS–Chem provides chemical modules for data assimilation of tropospheric composition at the NASA GMAO.