Regional Ensemble Reanalysis

Abstract:

As a partner in the EU funded project UERRA (Uncertainties in Ensembles of Regional Reanalyses), the Met Office will produce an ensemble of atmospheric regional reanalyses over Europe. Data from this ensemble will be incorporated into an ensemble data assimilation (hybrid 4DVAR) scheme to drive a high resolution, 12km, deterministic regional reanalysis. Both the ensemble and the deterministic reanalysis will cover the satellite era (1978-2017), producing a wide range of atmospheric variables from the surface to 80km.

The UERRA project will be the first time that an ensemble scheme has been used for regional reanalysis. The ensemble will provide users with a valuable measure of uncertainty in regional reanalysis over Europe. It will also provide hybrid 4DVAR with "errors of the day" so that the deterministic assimilation can benefit from flow-dependent background error covariances. To ensure a high quality product, the product must be validated. Validation of reanalyses can be problematic since independent high quality measures of "truth" are usually not available. Techniques for validation of ensemble reanalyses will be discussed.

Work already completed and plans for production will be outlined and the expected quality of the ensemble will be demonstrated, with reference to early results.