It was essential to develop a reliable production system capable of performing data assimilation very quickly. Using the combined experience of the Centre's Operations and Research Departments, the systems in use were studied carefully, slimmed down where necessary, modified to exploit a data archive as opposed to real-time data, and optimised for performance. This resulted in a prototype system capable of performing at the required rate, which was further refined and completed while being used as the principle vehicle for the initial ERA experimentation.

Once production began, late in 1994, the scientific emphasis gradually moved from experimentation to monitoring and validation. The external forcing fields were validated before the production started by means of maps, averages and time series. Every effort was made to detect, as early as possible, potential problems which would require further investigation. Where appropriate production was halted and re-started from an earlier date; in some cases production was allowed to continue, but the month or months concerned re-run at a later time. The production monitoring made use of a set of quality control tools, whose output, usually in the form of graphical information, was monitored continuously. All graphical and tabular monitoring results were kept both as hard copies and as files. Diaries were kept of all special events and problems encountered. Some of the monitoring performed is described in subsequent sections.

Production and monitoring continue throughout 1995 and into 1996. During the second quarter of 1996 the first pass through the full 15 years was completed. Monitoring enabled many errors which happened during the production to be located and rectified; nevertheless two lengthy periods needed to be re-run. First, the early production (to August 1980) was adversely affected by a bug, present also in the operational system, which significantly affected humidity at upper levels. Secondly, all cloud track wind data (SATOB) except the GMS data were accidentally excluded from June 1990 to October 1992, due to a change in their format within the ECMWF archive. A re-run of the first period was particularly desirable, as it presented an opportunity to run the FGGE year with the same observations and forcing fields as NCEP. Both re-runs were completed in September 1996.

The internal validation programme was augmented by setting up a number of external validation projects with the following partners:

Max Plank Institut für Meteorologie, Hamburg, Germany (MPI)
Hadley Centre, Meteorological Office, Bracknell, U.K. (UKMO)
Météo-France, Toulouse, France (DMN)
Danish Meteorological Institute, Copenhagen, Denmark (DMI)
Royal Netherlands Meteorological Institute, De Bilt, Netherlands (KNMI)
Instituto per lo studio delle Metodologie Geofisiche Ambientali, CNR, Modena, Italy (IMGA)
Atmospheric Dynamics Group, University of Bologna, Bologna, Italy (ADGB)

The continuous exchange of information between the ERA team and the validation partners has proved extremely useful. It will result in material being available to potential future users of the data which should be of considerable assistance.

Close co-operation has also been established between the ERA team and the teams responsible for the NCEP re-analysis, and the re-analysis performed by the NASA Data Assimilation Office.

16.11.2001