The Met Office Ensemble of Regional Reanalyses EMS 2015 The Met Office Ensemble of Regional Reanalyses Peter Jermey Dale Barker, Jemma Davie, Amy Doherty, Sana Mahmood, Adam Maycock, Richard Renshaw

Reanalysis at the Met Office 2008 & 2009 European Reanalysis 12km Deterministic Reanalysis 40 year European Reanalysis 12km Deterministic Reanalysis 20 member Ensemble Reanalysis

Uncertainties in Ensembles of Regional Reanalyses Ensemble using static 4DVAR Provides lower resolution fields with uncertainty estimation i.e. mean and spread at 24km Production start: Dec 2015 Deterministic reanalysis using hybrid 4DVAR Uses ensemble reanalysis uncertainty to improve assimilation (B) Provides higher resolution deterministic fields at 12km Production start: late 2016

Uncertainties in Ensembles of Regional Reanalyses Ensemble & Deterministic systems coupled 4DVAR minimises weighted sum of differences with background & obs Weights are dependent on background error covariance matrix (B) Ensemble uses fixed bg error cov (B=Bc) Ensemble provides EOTD to ensemble EDA - "hybrid" 4DVAR - weighted sum of bg error covs (B=bcBc+beBe) Bc + Be H 4 Y D B V R A I R D 4 D V A R 4 D V A R 4 D V A R UM UM UM UM

Ensemble System Represent every uncertainty in the system via perturbations Uncertainty in Observations Model Boundary Conditions Each ensemble member has a different realisation of these Set of (input) realisations represent the span of all possible realisations Therefore (output) spread should estimate uncertainty in the system

Observations For every observation we have a measurement and an uncertainty estimate... To obtain several realisations randomly perturb the measurement within the uncertainty estimate...

Model To perturb the model we need an estimate of model error... Assuming the analyses are drawn from the same distribution as the truth.

Boundary Conditions * * 80km *planned

RMS v Spread T2 & 500H (10 members) Germany Temperature 1.5m Geopotential Height 500hPa

Examples of Product 18Z on 18/02/10 mean uncertainty

Probability Maps Probability 50m wind 3ms-1 < speed < 15ms-1 >0.9 <0.1 Probability 50m wind 3ms-1 < speed < 15ms-1 18Z on 18/02/10 Probability of 1mm/6h 12Z to 18Z 18/02/10

Improve quality of ensemble What’s Next ..? Improve quality of ensemble Port to ECMWF Regional SURF Ensemble production aim to start December 2015 Regional hybrid Deterministic production aim to start late 2016

Thank you for listening

Initial Test Run (no inflation) T2 & 500H 1. Each member equally likely 2. Mean Error < Ctrl Error 3. En Spread = Mean RMSE 4. Model Freq. = Obs. Freq. 500H T2