ERA-40 Project Plan Summary

1. SUMMARY

ERA-40 will use a variational data assimilation system to make a new synthesis of the in-situ and remotely-sensed measurements made over the period since mid-1957, when a major improvement was made to the atmospheric observing system in preparation for the International Geophysical Year, 1958. ERA-40 will produce analyses with six hourly frequency throughout the period, supplemented by intermediate three-hour forecasts. The products will be of high temporal and spatial resolution, with a grid-spacing close to 125km in the horizontal and with sixty levels in the vertical located between the surface and a height of about 65km. The basic analysed variables will include not only the conventional meteorological wind, temperature and humidity fields, but also stratospheric ozone and ocean-wave and soil conditions. Additional information will be produced concerning the quality of both the observations used and the analyses generated. A sophisticated archival/retrieval system will be used to store the results and make them widely available. Compact sub-sets of the data will be generated to reduce data retrieval costs. Extensive documentation will enable customers and users of the results to gain maximum benefit.

ERA-40 will adopt innovative analysis techniques, especially with respect to satellite data, and will use new types of observation and improved specifications of sea-surface temperatures and sea-ice distributions. It will build on experience gained earlier in carrying out re-analysis in Europe and the USA, and will deliver products that are unique in their combination of time-range, vertical extent, variety and accuracy.

For overlap periods of at least one year, ERA-40 will produce analyses with and without each significant addition to the observing system. This will enable assessment and quantification of the impact of these enhancements, and in particular will document the benefit of the development of the satellite observing system over the past three decades. The availability of ERA-40 analyses will also revitalize the use of data from past field experiments in the improvement of climate and weather forecasting models. ERA-40 products will be enhanced by short periods of higher resolution global assimilation. This will enable better exploitation of the observational data from experiments such as GATE (1974),ALPEX (1982) and TOGA-COARE (1992-93).

Validation and demonstration studies form an important component of ERA-40. A major aim of these is to provide checks on the quality of the analyses by comparison with independent measurements. This will be done either by direct verification of analysed or simply-derived values, or by verifying the output of different types of model that have been forced by the analysed values, for example an ocean circulation model and a snow model. This verification will be complemented by a selection of diagnostic, process and climatological studies based on the analyses which will not only provide examples to the general user of the ways in which the data can be applied, but also provide specific contributions towards meeting some of the broader targets of the European Union's Fifth Framework Work Programme in Energy, Environment and Sustainable Development. The studies will focus on trends in the observing system, the hydrological cycle, clear-sky radiation, Alpine snow simulation, upper-tropospheric and stratospheric ozone and water vapour, ocean waves, global mass, heat, energy and moisture budgets, and diagnosis of atmospheric circulation systems.

The ERA-40 analyses will, however, have a wider applicability than can be explored in the studies to be carried out under this project, and they will be used by a number of other projects under the Work Programme, ensuring effective application across a range of studies.

The need for a project with the objectives of ERA-40 was recognised by the Euroclivar concerted action funded under the Fourth Framework Work Programme. Euroclivar "strongly recommended that a new 40-year re-analysis be made in Europe in the next five years" (Bengtsson and Komen, 1997; Anderson et al., 1998). ERA-40 is thus expected to make a significant contribution to those objectives of the Fifth Framework Work Programme that match the objectives of the CLIVAR component of the World Climate Research Programme, either directly or by providing data in support of projects such as DEMETER, which will explore the potential for seasonal prediction, and PROMISE, which will make extensive use of ERA-40 analyses for validating climate and seasonal prediction models and for driving crop models for impact studies. Other research areas with strong potential for application of the ERA-40 analyses include ozone depletion and other aspects of atmospheric chemistry.

The partnership carrying out the project comprises the European Centre for Medium-Range Weather Forecasts (ECMWF), the national weather services of France (Météo-France), the Netherlands (Koninklijk Nederlands Meteorologisch Instituut, KNMI) and the United Kingdom (the Meteorological Office, UKMO), meteorological research institutes from Germany (Max-Planck-Institut für Meteorologie, MPIfM) and the USA (National Center for Atmospheric Research, NCAR), and the Meteorology Department of the University of Reading, UK (UREADMY). ECMWF has made extensive preparations for ERA-40, and will be the producer of the analyses and co-ordinator of the project. The other partners have been active in the planning and the preliminary studies for the project, and will carry out the bulk of the validation, diagnostic and exploitation studies. NCAR has also played an essential rôle in supplying ECMWF with observational data not previously held in the ECMWF archives.

Support for ERA-40 has been committed by a number of bodies in addition to the European Union:

The partners in this project have supported the acquisition and preparation of the necessary observations, the trial production and validation of analyses, the assessment of user requirements and the general planning of the project.
Institutions in China (IAP), Japan (JMA) and the USA (PCMDI) are funding the secondment of staff to work on the project.
Several other institutions have provided specific holdings of past observational data.
Fujitsu Ltd is providing substantial computing support for the project.
EUMETSAT has committed to re-deriving winds from Meteosat-2 images for the period 1981-1988.
The World Climate Research Programme and the Global Climate Observing System are providing funds in support of an External Advisory Group for the project. The Group has already met twice, in January 1998 and March 1999, to aid in the planning of the project, including the assessment of user requirements.

The capacity of the partners and these supporting institutions to provide ongoing manpower support for ERA-40 is limited. In particular, it is insufficient to meet the challenging objective of producing the re-analyses at a rate fast enough to satisfy the demand for ERA-40 products both from Fifth Framework research projects and from the wider scientific community. Re-analysis projects must proceed at sufficient speed for them not to be continually overtaken by developments in data-assimilation technique and large-scale computing. Accordingly, the funding from the EU under the Fifth Framework Programme will be used to enable the basic production of the re-analyses to be completed within a period of about two years, and to enable the necessary validation and demonstration studies to be undertaken.

The preparatory work for the project is now largely complete, enabling production of the ERA-40 analyses to commence close to the start of the EU-funded phase of the project, designated month 0. The subsequent principal milestones and direct results of the project are:

Production rate rising to two analysed years per month by month 11.
Analyses for 1987-1998 and 1957-1968 completed, monitored and archived by month 14.
Interim validation and exploitation reports in month 17.
Mid-project workshop to present project and interim results to users.
Complete archive of analyses for 1957-2001 by month 31.
Affordable data dissemination service by month 35.
Full delivery of climate and statistical data by month 35.
Final validation, exploitation and project reports in month 35.