1. FIRST GEOS-CHEM USERS’ MEETING June 2-3 2003
Why are we here?
Exchange model information and experience
Identify priorities for model development
Establish protocols for code management and development, relationships between users
The GEOS-CHEM user community

2. HERITAGE OF GEOS-CHEM MODEL
Harvard-GISS CTM
(Prather et al., 1987)
Sulfate simulation
(Chin et al., 1996)
Tropospheric O3 simulation
(Horowitz et al., 1998; Liang et al., 1998; Wang et al., 1998)
CO2 simulation
(Suntharalingam
et al )
GEOS-CTM
(Allen et al., 1996)
GEOS-CHEM CTM
for tropospheric O3
(Bey et al., 2001)
GOCART aerosol model (Chin et al., 2000)
Current GEOS-CHEM CTM
fvGCM at GMAO
(data assimilation)
NASA GMI (assessment)
CACTUS
(chem-climate)
EPA CMAQ
(regional air quality)

3. CURRENT GEOS-CHEM MODEL CAPABILITIES
Goddard Earth Observing System (GEOS) global assimilated meteorological data, 1983-present including forecasts
TPCORE advection, GEOS convective mass flux and PBL diagnostics
Resolution: 1ox1o--4ox5o horizontal, layers in vertical, nested capability g 1ox1o
Mature applications:
Tropospheric O3-NOx-VOC chemistry
Aerosols coupled to chemistry
CO2, CH4
Oxygenated organics, nitriles, methyl iodide
Under construction:
fvDAS simulation capability (for 11/02-present)
Linkage to CMAQ regional model
Stratospheric chemistry
Mercury
Methyl bromide, chloride
Linkage to chemical data assimilation at GMAO
Planned:
Aerosol microphysics
Coupling to GISS GCM meterological fields
Hydrogen
POPs

4. GEOS-CHEM DEVELOPMENT APPROACH
Close association with NASA Global Modeling & Assimilation Office (GMAO)
use GMAO/GEOS meteorological data sets and transport schemes
Model versions updated frequently to keep up with state of science and to increase traceability
benchmarking of code, single gatekeeper (Bob Y.) to minimize errors
users encouraged to update to latest version as they can. No dedicated effort to support old versions.
Encouragement of multi-institutional user community, user-friendliness, support
free distribution of code to competent users
users’ guide
web site
Bob Yantosca

5. VISION FOR GEOS-CHEM
A “living CTM” focused on pushing the frontiers of knowledge of global atmospheric composition
“living CTM” , “pushing the frontiers” means nimble and vigorous approach to code development and update
““global” as opposed to “regional”
“atmospheric composition” in the broadest sense
A tool for supporting other activities:
assessments (GMI)
satellite retrievals (NASA, CSA, ESA)
regional air quality models (CMAQ)
data assimilation (GMAO)
climate models (GISS)
How is this to be supported?
GEOS-CHEM is a grass-roots model. It needs to be supported by its community (“consortium” a better word?): user participation, ownership, responsibility, feedback are essential
Central management can be provided by Harvard (Jacob/Yantosca) for foreseeable future

6. A PROPOSED MANAGEMENT CHARTER FOR GEOS-CHEM
Model scientist (Jacob) is responsible in consultation with users for
code integrity
development prioritization
relationships in user community, issues of general benefit
admission of new users
Model programmer (Yantosca) is responsible for
maintenance of standard version
code updates
user support
interface with GMAO
Users are responsible for
maintaining communication with other users (web site)
updating regularly to latest version of model
giving credit to developers in publications
not distributing code
Developers are responsible for
providing codes and data sets (when mature) for implementation in standard version
working with model programmer in this implementation
updating to new standard version (no growing parallel versions of code!)