Proceedings of the ECMWF workshop on flow-dependent aspects of data assimilation, 11 - 13 June 2007.

Includes bibliographical references.

The aim of the workshop was to bring together European and American experts to discuss ways in which the ECMWF analysis could be made more responsive to observations in those particular locations where significant and potentially severe weather is developing. These locations vary from day to day depending on he 'flow', i.e. the atmospheric conditions. It is where the model uncertainty is large that good observations :an provide the most beneficial corrections to the model fields through flow-dependent data assimilation. Ensemble-based methods are well suited to detect and track these areas of higher observation significance as evolve and develop. The working group participants discussed the techniques for running ensembles of assimilations: how the various sources of error could be represented and accounted for. The workshop Recommendations will influence the ECMWF research plans in this area, suggesting the avenues to explore and the priorities for the next couple of years. Groups were set up to consider the subjects of ''Variable transformations", and the ''Principles'' and "Implementation issues" of using ensemble-based covariances in 4D-Var.

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