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Trials of the Met Office 4DEnVar system

Adam Clayton (Met Office)

The Met Office - the UK's National Weather Service - is developing a global hybrid 4D-Ensemble-Var (4DEnVar) system as a potential replacement for the hybrid-4DVar scheme used operationally since 2011. Using ensemble data generated by the operational EPS (MOGREPS), a series of trials has been run to test the sensitivity to

1. Ensemble size (23 or 176 members) and weighting towards the ensemble covariance.
2. Alternative localisation schemes, including spatial/spectral localisation (Buehner 2012, MWR), in which the ensemble is split into overlapping horizontal wavebands and localised independently.
3. A correction to columnar mass-divergence imbalances caused by vertical calisation.

After describing the basic design and computational performance of the system, results from these trails will be presented and analysed.