ECMWF/GEO Workshop on Atmospheric Reanalysis

1. ECMWF/GEO Workshop on Atmospheric Reanalysis • Held at ECMWF, 19-22 June 2006 • Programme for the meeting was developed in liaison with WOAP and AOPC • Followed: • 2005 NASA/NOAA/NSF Workshop on the Development of Improved Observational Data Sets for Reanalysis • 2005 ECMWF/NWP-SAF Workshop on Bias Estimation and Correction in Data Assimilation • 2005 ECMWF Workshop on a potential European Regional Reanalysis project (EURRA) • 2006 SCAR/CliC/ICPM Workshop on High Latitude Reanalysis ECMW/GEO Workshop on Atmospheric Reanalysis

2. ECMWF/GEO Workshop on Atmospheric Reanalysis • 21 participants from outside ECMWF (including Kent, Lorenc and Trenberth from WOAP) • 29 presentations covering: • Experience and plans of reanalysis centres • Status and needs for reanalysis: user views • Developments in data assimilation for reanalysis • Observations and boundary forcing fields • Other aspects • Presentations may be viewed at • http://www.ecmwf.int/newsevents/meetings/workshops/ ECMW/GEO Workshop on Atmospheric Reanalysis

3. Plenary Discussion – User Aspects • The user base • The number of users of reanalysis products is considerable • User base is broad, and extends well beyond climate research community • Specific user requirements • Full range of user activities was not represented, but workshop discussed: • Dynamical processes • High-latitude processes • Analysis quality for pre-satellite era • Chemical transport modelling • Long-term continuity and balance • Horizontal resolution • Additional output products • Precipitation and surface fields ECMW/GEO Workshop on Atmospheric Reanalysis

4. Plenary Discussion – User Aspects • General user requirements • Comprehensive documentation of reanalyses • Mechanism for exchange of information originating from users • Measures of expected accuracy or uncertainty • Statistical correction of products • Continuation in CDAS mode • Remote access to data assimilation system to perform OSEs • Involvement in User Advisory Groups • Period for future reanalysis • For many users, satellite era is sufficient – and improvements are still needed here • Some interest in data back to 1940s or 1930s • Reanalysis further back in time based on analysis of only surface data is feasible ECMW/GEO Workshop on Atmospheric Reanalysis

5. Plenary Discussion – Observations and boundary and forcing fields • Observations for assimilation in reanalyses • Working Group on ‘The On-going Development of Improved Observational Data Sets for Reanalysis’ supported • Distributed data centres working to common, managed standards and purpose, including feedback from reanalysis centres • Satellite requirements essentially covered by supplement to the GCOS Implementation Plan • Data recovery needs to continue • Data from field experiments or reference observation sites are needed, preferably in near-real-time for monitoring and use in CDASs • Also considered: • Homogenisation of radiosonde data • Sea-surface temperature and sea-ice distributions • Vegetation • Snow cover • Precipitation • Composition ECMW/GEO Workshop on Atmospheric Reanalysis

6. Plenary Discussion – Data assimilation • Long-window, weak-constraint 4D-var • Error estimation • to provide information for users • for adaptive specification of analysis statistics • Adaptive correction of: • model biases • observational biases • Monitoring • Coupled assimilation • ocean waves, ocean circulation, land surface, CTMs ECMW/GEO Workshop on Atmospheric Reanalysis

7. Plenary Discussion – Organizational issues • International coordination • Role of WOAP and AOPC • Issues are essentially as discussed in last year’s WOAP paper • Healthy level of collaboration between reanalysis teams (and with data providers) at the working level • Data policy issues were not discussed systematically, but points raised have been built into report, drawing on policy from ten-year implementation plan for GEOSS • Need for long-term institutional funding for reanalysis • Lifetime of a particular reanalysis can be a decade or more • Expertise and experience should be maintained • Ongoing advocacy for reanalysis from the committees, panels and working groups of GEO, GCOS and WCRP is still necessary ECMW/GEO Workshop on Atmospheric Reanalysis