1. 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

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

3. 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

4. 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

5. 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

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

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

8. Boundary Conditions * *
80km
*planned

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

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

11. 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

12. 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

13. Thank you for listening

14. 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