The NASA Global Earth Observing System Composition Forecast (GEOS-CF) system provides near-real time (NRT) analysis and 5-day forecasts of a wide range of atmospheric constituents at a horizontal resolution of 0.25 degrees (about 25 km) from the surface to 0.01 hPa (about 80 km). A full model description and evaluation of the GEOS-CF tropospheric simulation and forecast skill is given in Keller et al. (2021), while Knowland et al. (2022) provides a description and evaluation of stratospheric composition.

GEOS-CF combines the GEOS weather analysis and forecasting system (Molod et al., 2015) with the GEOS-Chem (Hu et al., 2018; Long et al., 2015) and Goddard Chemistry, Aerosol Radiation and Transport (GOCART; Colarco et al., 2010) chemistry modules. The GEOS-CF system is run once per day, replaying to the GEOS for Instrument Teams (GEOS-IT) analyzed meteorological fields (Orbe et al., 2017). 

Starting with version 2, GEOS-CF assimilates stratospheric O₃ profiles and total columns, currently from the Microwave Limb Sounder (MLS, v5) and Ozone Monitoring Instrument (OMI, V003), respectively, both onboard NASA’s Aura satellite. Observations are assimilated within the GEOS data assimilation system using the Gridpoint Statistical Interpolation module (Purser et al., 2003; Wu et al., 2002) in 6 hourly increments with background O3 fields provided by GEOS-Chem. 

Upon completion of the meteorological replay and constituent assimilation, a five-day free-running model forecast simulation is launched, using persisted sea ice concentrations, sea surface temperatures, and biomass burning emissions.  

The diagram above illustrates the components of the GEOS-CF (version 2) system and provides a timeline of how the system is run. A forecast is initialized daily from 9Z, with replay and assimilation proceeding in 6-hour windows from 9Z on the previous day, and the forecast extending out to 120 hours from the initialization time. 

GEOS-CF was made possible by the inclusion of the GEOS-Chem chemistry model into GEOS. While building on GMAO’s core capabilities, GEOS-CF also illustrates how collaborative research can lead to the development of new GEOS products. A series of projects funded by NASA has supported GMAO’s collaboration with Harvard University, through which the HEMCO emissions module and the GEOS-Chem code base have been developed (see http://www.geos-chem.org/). These code bases are shared in Git repositories, which facilitates common developments by the GMAO and the GEOS-Chem community and simultaneously allows the same code base to be used by the academic research community and the GEOS systems in the GMAO.

• Further details are provided in journal articles describing the GEOS-CF system, as well as the file specification documents; these can be found on the Documentation page.

Major Updates

In October 2025, a major update to the GEOS-CF system was finalized. This included an update of GEOS-Chem from version 12.0.1 to 14.0.0, an update to HEMCO 3.0 (Lin et al., 2021), an update of anthropogenic emissions to the Community Emissions Data System (CEDS) inventory (v2021_v04: O’Rourke et al., 2021), an update of aircraft emissions to the 2019 Aircraft Emissions Inventory Code (AEIC) monthly climatology (Simone et al., 2013), and an update in biomass burning emissions to the near-real time Quick Fire Emission Database (QFED) v2.5 (Darmenov and da Silva, 2015; Andreae 2019). Constituent assimilation of O₃ total columns and profiles was also implemented during this update, as well as the addition of carbon dioxide (CO₂) and methane (CH₄) forecasts. More details are provided in the file specification for this version on the Documentation page.

A priority for future versions of GEOS-CF is to increase the horizontal and vertical resolution and include assimilation of additional observations of atmospheric composition using the newly developed Joint Effort for Data assimilation Integration (JEDI) framework. Future versions of GEOS-CF will also be more tightly coupled to GMAO’s forefront meteorological assimilation system, GEOS-FP. Following the end of the Aura mission, the GEOS-CF system will switch to assimilating O₃ columns from the OMPS Nadir Mapper (OMPS-NM) and profiles from the OMPS Limb Profiler (OMPS-LP).