FIRST GEOS-CHEM USERS’ MEETING June 2-3 2003

1. FIRST GEOS-CHEM USERS’ MEETINGJune 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. Harvard-GISS CTM (Prather et al., 1987) HERITAGE OF GEOS-CHEM MODEL 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.. 2003) 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, 20-72 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. 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 GEOS-CHEM DEVELOPMENT APPROACH

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!)