1. GEOS-Chem Chemical Transport Model: Current Status and Future Plans Daniel J. Jacob, GEOS-Chem Model Scientist Harvard University

2. Chemistry, Aerosols, and Climate: Tropospheric Unified Simulation (CACTUS) Science Team Meeting at Caltech, 1998

3. GEOS-Chem Chemical Transport Model (CTM) Input data NASA GEOS meteorological fields other Modules emissions transport chemistry aerosols deposition sub-surface Solve 3-D chemical continuity equations on global Eulerian grid Applications chemical processes, transport, budgets inverse analyses radiative forcing air quality biogeochemistry … Model adjoint Ozone-OH-NO x -aerosol chemistry, aerosol microphysics, carbon gases, mercury, … 1980-present GEOS meteorological data, future and paleoclimates (GISS GCM) Horizontal resolution: 1/4 o x5/16 o (native), 1/2 o x2/3 o (native), 1 o x1 o, 2 o x2.5 o, 4 o x5 o Adjoint model for inverse/sensitivity analyses Nested model for continental-scale simulations Capabilities of present standard model: Nested model

4. GEOS-Chem contributes to broader Earth science activities GEOS-Chem Collaboration with other CTMs module exchanges intercomparisons Local air quality models outer nest Aircraft and satellite missions forecasting and data analysis a priori infomation Chemistry-climate interactions Two-way interface with GCMs Data assimilation systems Chemical data assimilation Earth system models Atmospheric chemistry module

5. The GEOS-Chem user community: 72 institutions, 18 countries The model is managed by a GEOS-Chem Support Team based at Harvard (Bob Yantosca, Mike Long, Melissa Payer), Dalhousie University in Canada (Sajeev Philip) and University of Colorado (Nicolas Bousserez, adjoint model) Scientific oversight is by a 22-member Steering Committee including Hong Liao (Co-Chair, Chemistry-Climate Working Group) and Yuxuan Wang (Co-Chair, Nested Model Working Group) Developments by user community are rapidly integrated into standard version Strong model integrity is maintained by version control and benchmarking, Extensive networking between users, GEOS-Chem meetings every two years

6. China’s presence in the GEOS-Chem user community is rapidly growing Chinese scientists are important contributors to GEOS-Chem

7. Functioning of the GEOS-Chem community GEOS-Chem is a grass-roots community model –Code is open-access, extensively documented and supported –All model development is initiated by users to serve their research needs –New developments are promptly implemented in the standard model –Young scientists have opportunity to get involved in model development Strong model management maintains model unity, traceability, state of science –GEOS-Chem Support Team maintains standard model: new developments, benchmarking, version control, user support –Support Team is funded by NASA (1 FTE) and NSERC (0.5 FTE); strong leverage from community volunteerism is essential –GEOS-Chem Steering Committee monitors model development, promotes good practices and communication, leads Working Groups The model is owned by its users, and with ownership comes responsibilities: –Keep up with the model (newsletters, wiki, working groups, IGC meetings) –Contribute to the community: help with requests, report bugs… –Share mature developments for incorporation into standard model –Update regularly to latest standard version of model –Be generous in credit to developers The success of GEOS-Chem relies on the spirit of its user community!

8. Development of grid-independent GEOS-Chem model Grid-independent GEOS-Chem Transport (GCM or other) o Grid-independent model computes chemical updates on any grid to pass on to a GCM o Allows flexible coupling to different dynamical cores for data assimilation, climate modeling o Presently developed for coupling with NASA GEOS data assimilation system using ESMF interface o Facilitates massively parallel implementation through MPI o Has been developed as part of the standard GEOS-Chem model; will eventually replace standard model in a way transparent to users

9. Future directions for GEOS-Chem Continued improvement of core model Organic gas+aerosol chemistry, aerosol microphysics, … Software improvements Grid-independent model to enable MPI parallelization New chemical solvers to speed up code Expansion of model capabilities Stratospheric chemistry, radiative forcing, two-way nesting, biogeochemical cycling Coupling with meteorological models Chemistry-climate interactions, chemical data assimilation Operational applications Carbon monitoring system (model adjoint), air quality forecasting…