The CHEmistry and Emissions REanalysis Interface with Observations (CHEEREIO) is a package that wraps the GEOS-Chem chemical transport model source code. After a simple modification of a single configuration file (ens_config.json), CHEEREIO automatically produces and compiles an ensemble of GEOS-Chem run directories. Each ensemble member comes with a randomized set of gridded emissions scaling factors, drawn from a prior distribution reflecting user-specified emissions uncertainties, for the set of species specified by the user. As the ensemble of runs progresses, CHEEREIO will periodically pause the ensemble, compare with a set of observations (i.e. satellite, surface, and/or aircraft), and update relevant emissions scaling factors and chemical concentrations to best match reality given the uncertainties of measurements and model. CHEEREIO calculates this update via the localized ensemble transform Kalman filter (LETKF) as described in Hunt. et. al., [2007]. Because this approach is model agnostic (specifically, it does not rely on the adjoint), CHEEREIO supports emissions updates and chemical concentration corrections for arbitrary configurations of the GEOS-Chem model. However, the current CHEEREIO codebase assumes that GEOS-Chem code is version 13.0.0 or later.
For an extensive technical and mathematical overview of CHEEREIO, see the online documentation or the model description paper. The CHEEREIO implementation of LETKF is described in detail in the documentation, but all simulations follow the same basic workflow in the figure below.
Plain language description
The GEOS-Chem CHEmistry and Emissions REanalysis Interface with Observations (CHEEREIO) is a tool that allows scientists to use observations of pollutants or gases in the atmosphere, such as from satellites or surface stations, to update supercomputer models that simulate the Earth. Other scientists have assembled estimates of emissions of various pollutants from around the world, but our emissions estimates are very uncertain. CHEEREIO uses a model called GEOS-Chem to simulate what the atmosphere would look like if those emissions estimates were correct, and then compares those estimates to the real atmosphere as observed by satellites or equipment on the Earth’s surface. CHEEREIO uses the difference between the model simulation and the real world to update our maps of emissions. CHEEREIO can correct other aspects of atmospheric models, too, not just emissions.
CHEEREIO can be downloaded from our Github page and installed by following the instructions in the documentation.
CHEEREIO follows four design principles:
- Easy to customize: Assimilate anything, in any GEOS-Chem configuration or simulation.
- Easy to maintain: Science automatically aligned with latest model version. No updating separate model adjoint code!
- Easy to deploy: One configuration file controls installation and settings
- Easy to link observations: Object-oriented observation operator implementation in Python allows the user to rapidly add new kinds of data with minimal programming required.