1. Recent & planned developments to the Met Office Global and Regional Ensemble Prediction System (MOGREPS)
Richard Swinbank,
Warren Tennant, Sarah Beare, Christine Johnson, Neill Bowler, Ken Mylne, Nigel Roberts and Adam Clayton
GIFS-TIGGE Working Group meeting #9, Sept 2011
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2. MOGREPS – The Met Office ensemble
24-member ensemble designed for short-range forecasting
Regional ensemble over Atlantic and Europe (NAE) to T+54 at 06Z and 18Z (18km grid, 70 levels)
Global ensemble to T+72 at 00Z and 12Z (~60 km grid, 70 levels)
Medium-range version of MOGREPS-G: MOGREPS-15, used for TIGGE.
ETKF for initial condition perturbations
Stochastic physics
Aim to assess uncertainty in short-range, eg.:
Rapid cyclogenesis
Local details (wind etc)
Precipitation
Fog and cloud
NAE
Starting point for the storm surge ensemble is our short-range atmospheric ensemble.
Describes resolutions applicable to results shown here; planned to upgrade to ~18 km this year with new supercomputer.
Analysis uncertainty sampled using Ensemble Transform Kalman Filter, which estimates the impact of observations on the background uncertainty estimated by the previous ensemble run, based on the same maths underlying data assimilation. Aims to produce an ensemble correctly calibrated from T+0, unlike initial growth phase of singular vector perturbation (not perfect in achieving this, of course). Stochastic physics to capture some of the errors associated with model evolution.
MOGREPS has been running since August 2005, and was made Operational in September 2008.
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3. Recent ( ) upgrades
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4. Increased MOGREPS resolution (2010)
Global N144 (~90km) to N216 (~60km)
Regional (NAE) 24km to 18km
Both systems 38L to 70L:
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5. Summary of 2010 MOGREPS upgrades - not just resolution changes
Global
Regional
PS23
(Spring)
N144L38 to N216L70
L70 physics changes
SKEB2 implementation
ETKF vertical localisation
MOGREPS-15 as Global
NAE 24km L38 to 18km L38
minimal physics changes
PS24
(Summer)
IAU - Increments added at T+0
ETKF & OPS changes
RP2 – additional BL parameters
SKEB2 – add KE term
NAE 18km L38 to 18km L70
Physics changes for L70
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6. IAU (Incremental Analysis Update)
The IAU was originally developed to add unbalanced (3DVar) analysis increments to the background state.
MOGREPS uses the technique to add initial perturbations. The increment is added in gradually over time to damp fast gravity waves.
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7. MOGREPS global ensemble
MOGREPS-G uses the ETKF to generate perturbations. These are then added to the reconfigured global analysis to create the set of the ensemble members.
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8. Ranked Probability Score
RPS is similar to mean-square-error but measuring probabilities over a range of thresholds.
Precip
T850
No IAU gives improvement for precip but degradation for T850.
control
No IAU
Shifted IAU
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9. Met Office hybrid implementation (Adam Clayton, Dale Barker, Andrew Lorenc, ...)
Basic details:
“Alpha control variable” hybrid, with localisation in control variable space (streamfunction, velocity potential, unbalanced pressure, humidity).
23 error modes from MOGREPS-G.
Static localisation in horizontal and vertical.
80% climatological / 50% ensemble covariance. (Total variance inflated to maintain analysis fit to obs.)
Performance: ~1% improvement against obs and ECMWF analyses.
Operational implementation: July 2011.
Dec uncoupled (29 days)
Jun coupled (28 days)
RMSE changes vs. obs:
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10. Future upgrades
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11. Plans for MOGREPS changes following HPC mid-life upgrade
Allows further improvements in resolution of operational forecast models
For MOGREPS we will use a two-step nesting strategy:
Global ensemble MOGREPS-G grid ~40 km
Regional ensemble MOGREPS-EU ~12 km
UK convective-scale ensemble MOGREPS-UK 2.2 km
The short-range ensemble forecasts will run four times a day, with 12 members (1 control + 11 perturbed)
Products calculated from pairs of lagged forecasts
The ETKF will use 22 (later, more) perturbed members with a 6-hour cycle
MOGREPS-15 will continue to run twice a day
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12. Proposed (schematic) schedule
Each configuration to run 3 hours after driving ensemble to obtain freshest boundary conditions.
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13. Proposed new MOGREPS-EU domain
Aim to use 12km grid for MOGREPS-EU, so that MOGREPS-EU control run can directly replace 12km NAE – to be retired
Adopt new set of 70 levels to improve resolution in lower troposphere
Also used for EURO4M reanalysis project, covering EEA countries & Mediterranean.
Covers Storm Surge and ocean Atlantic Margin model domains
Will investigate sensitivity to western boundary.
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14. UKV Model Domain for MOGREPS-UK
Variable resolution, 2.2km in inner domain
Based on 1.5km UKV model used for convective-scale deterministic forecasting
Same 70-level set as MOGREPS-EU
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15. Implementation schedule
Originally planned as “big bang” implementation at PS29 (Spring 2012), but due to delay in IBM P7 delivery, implementation will be phased:
PS28 (Autumn 2011)
4 cycles per day with current models, but using new schedule.
PS30 (late Spring 2012)
Introduce MOGREPS-UK in time for Olympics
PS31 (Autumn 2012)
MOGREPS-EU
Other resolution & physics changes at PS31 or PS32
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16. Medium-range and Seamless Forecasting
Currently the medium-range ensemble, MOGREPS-15 is essentially the same as MOGREPS-G but run to 15 days using UK member-state computer time at ECMWF.
Met Office strategy is to make forecasts consistent across different timescales, from short-range NWP to climate prediction.
We are planning to bring together ensemble prediction systems on the medium-range and monthly to seasonal timescales, including.
Initial condition perturbations from ETKF and, in longer term, Ensemble Data Assimilation System;
Coupled model to better represent ocean-atmosphere interactions.
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17. Schematic of possible coupled medium-range/ monthly/ seasonal EPS
Suite 1
20 members
15 days
Suite 2
2 members
2 months
Suite 3
2 members
7 months
Suite 4
X members Hindcast
Medium-range
products
Monthly
products
Seasonal
products
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18. Any Questions?
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