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ERA-40 Archive Document



Archiving for ERA-40 takes as its basis the general archiving policy of ECMWF, which has evolved over more than 20 years of storing operational analyses and forecasts for subsequent use both for ECMWF<92>s own activities and for activities within its Member States. This policy has been reviewed from time to time by the Scientific and Technical Advisory Committees of ECMWF, most recently in sessions in 1999 and 2000. Archiving for ERA-40 also builds on experience gained from carrying out ERA-15, including the feedback received from users of this earlier re-analysis.

Developing an archive plan must take account both of product-generation costs and of constraints on archive volume and retrieval capability. The hardware and media-volume available for data handling at ECMWF places an upper limit on what may be saved.

As with the preparation of the data assimilation system for ERA-40, drafts of the Archive Plan have been reviewed by members of the Steering and External Advisory Groups, and the Plan was presented to the user community at the Second International Conference on Re-analyses. It includes a number of additions to what has been stored up to now from the operational data assimilation and forecasts, and to what was stored for ERA-15. These include both additional products within the conventional streams of output data and a number of new streams of products proposed by the validation partners (Steering Group members), who represent particular classes of users. The new streams comprise:

    • · fields on isentropic and PV=2 surfaces;
    • · clear-sky radiation fields;
    • · vertical integrals for energy, mass, water and ozone budgets;
    • · additional fields derived during short-range forecasts for support of chemical-transport modelling and other trajectory studies.

In addition, detailed grid-point and area-mean diagnostics are being produced for the field- measurement sites and river basins. The additional fields for support of chemical-transport modelling were in fact proposed in a letter supported by a total of eleven European user groups, including four of the validation partners.

The plan for a time-series component of the archive was drawn up partly to support a basic requirement for quick-look graphical products, but more importantly to facilitate the use of atmospheric and land- surface products in seasonal forecasting studies, including the driving of crop and disease models. The list of products is based on one drawn up at the kick-off meeting for the DEMETER project (also funded by the EU under the Fifth Framework Programme), with input at that meeting provided also on behalf of the similarly-funded project PROMISE. Ocean-wave products were included in this component of the archive following an initial request from the Maritime Administration of Iceland during routine contacts with this Co-operating State of ECMWF. Vertically-integrated water-vapour fluxes were added in view of the widespread computation of such fluxes by users of the earlier re-analyses.

The time series, other new product streams and streams of data on the lower-resolution 2.5° latitude/ longitude grid should all contribute to reducing the amount of data handling needed to satisfy the retrieval requests of many users. This should give the benefits of quicker retrieval times for those users with direct access to the ECMWF computer system, and lower handling charges for users obtaining products through ECMWF Data Services. It should similarly benefit users who obtain products through one of the arrangements for national data supply.

User-contacts have resulted in plans being developed with NASA to support the ISLSCP-II initiative concerning data for research on land-surface processes. Near-surface atmospheric and surface fields from ERA-40 will be evaluated on the standard 1° ISLSCP grid using interpolation appropriate to land products. NASA will produce a CD-ROM and provide other data services for this particular set of products.


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