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GloSea4:the new Met Office Seasonal Forecasting System A. Arribas, M. Glover, D. Peterson, A. Maidens, M. Gordon, C. MacLachlan, D. Fereday, W. Tennant …. and many more
July 2009
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Working on this during the last two and a half years … due to become operational in August …
Does it work?
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First ever GloSea4 forecast (initialised 25th May)
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Nino3 SST RMSE (lower=better)
1989-1999 period
GloSea3 15-membersECMWF-S3 9-membersGloSea4 6-members
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• GloSea4 is not a model– GloSea4 is fully integrated into the HadGEM3
development process. HadGEM3 needs to be improved for regional prediction for S2D
• GloSea4 is an Ensemble Prediction System– Predictability comes from initial conditions and
boundary forcings
– Uncertainty comes mainly from the model itself
Model: HadGEM3_AO_r1.1 Resolution: N96L38ORCA1L42
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GloSea3 vs. GloSea4
GloSea3 (current system) GloSea4 (new system)
Model HadCM3 (N48L19 – 1/3L40)
HadGEM3(N96L38-ORCA1L42)
Initialization Atmos/soil: ECMWFOcean: UM-ocean 3D-OI
Atmos/soil/sea-ice: Met OfficeOcean: NEMO 3D-OI
IC uncertainties Wind stress and SST perturbations added to a central analysis Weekly lagged approach
Model uncertainties None RP + SKEB2
Forecast ensemble 41-members (monthly bursts from 1st ) ~ 14 members per week
Hindcast ensembleRun a priori off-line
15-members / 15-years (1987-2001) ERA-40
Run on real-time
~3-members per week / ~14-years (1989-2002) ERA-interim
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We’ve changed everything to …
create a more flexible system,
fully integrated with model development
and better representing initial conditions and model uncertainties
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Current system (GloSea3)
1st Jan 1991
• Hindcast: Run apriori; 15 years; 15 members; 6-months forecasts
•Skill measurements
•Estimate mean errors to calibrate forecast
1st Jan 1992
1st Jan 2001
……………..
hindcast
Expensive: A total of ~1350 years of simulations
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Current system (GloSea3)
1st Jan 1991
• Hindcast: Run apriori; 15-yrs (87-01); 15 members; 6-months forecasts
• Forecast: Run real-time; Monthly; 40 members; 6-months forecasts
1st Jan 1992
1st Jan 2001
…………….. 1st Jan 2009
•Skill measurements
•Estimate mean errors to calibrate forecast
hindcast
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Problems with GloSea3:• Decoupled from model development
• Not flexible: Difficult to upgrade model/system
• Only one forecast each month
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New system (GloSea4)
15th Jan'09
22th Jan'09
8th Jan'09
1st Jan'09
15th Jan
22th Jan
8th
Jan 1st Jan
1989-2002
Assessment of skill and calibration on the fly
For
ecas
tH
ind
cast
• Hindcast: Run real time; ~ 14 yrs, ~3 members/week, 6-months fcst
• Forecast: Run real-time weekly; ~14 members/week, 6-months fcst.
No perturbations to ICs only model uncertainties
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GloSea4 Forecast Suite
Initial Conditions
Calculation
Post Processing
Get NWP 4D VAR data
Atmospheric reconfig.
Ocean DA
UM atmosphere
NEMO CICE
Archiving
Skill & calibration
Note: Data from Met Office NWP
Note: ODA run daily (same as FOAM but different resolution)
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GloSea4 Hindcast Suite
Initial Conditions
Calculation
Post Processing
ERA-inter. Atmos. data
Atmospheric reconfig.
Ocean data
UM atmosphere
NEMO CICE
Archiving
Skill & calibration
Note: Ocean data previously assimilated for all hindcast dates
Note: Data from ECMWF reanalysis
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Flexible: easy to upgrade
2009 2010 2011N96L38 N96L85 N216L85
120km / low lid 120 km / strat. 50 km / stratos.
ORCA1L42 ORCA0.25L91
- Improved representation of physical processes (e.g. monsoon) from MORPH3
- Increased resolution
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GloSea4: Its role in HadGEM3 development
• Fast-physics parameterizations (e.g. convection)
GloSea4 Hindcast Test-bed(initialized coupled forecasts)
• Main modes of variability, teleconnections, drifts
NWP
Climate
GloSea4 used in MORPH3 as a testing platform
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GloSea4: Its role in HadGEM3 development
obs
HadGEM3 (climate bias)
HadGEM3 (spin up)
GloSea4 (HadGEM3 seasonal)
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Benefits of GloSea4:• Linked to model development
• Easy to upgrade model/system
• Weekly forecast updates (seamless monthly system?)
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GloSea4 as an Ensemble Prediction System:
representing uncertainties
- Initial Conditions: Lagged approach
- Model uncertainties: Stoch. Physics
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GloSea4 : Initial conditions
Adding perturbations to a central analysis
degrades the quality of the initial conditions
….
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Pert. Members
CTRL
(Bowler, Arribas and Mylne, 2008. MWR)
GloSea4 : Problems adding perturbations to ICs
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• Avoid degradation of initial conditions (improved predictability?)
• Better representing true uncertainty (spatial and magnitude) in ICs
• Allows more frequent forecast updates
GloSea4 : Lagged approach,no perturbations to ICs
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Random Parameters:
• Structural uncertainties due to subjective parameters
Stochastic Kinetic Energy Backscatter v2.0:
• Sub-grid scale processes not represented by model
GloSea4: representing model uncertainties
Bowler et al. 2008. QJRMS
Shutts, 2005. QJRMS
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Ent.coef parameter
2
2.2
2.4
2.6
2.8
3
3.2
3.4
3.6
3.8
4
0 6 12 18 24 30 36 42 48 54 60 66
3-h timestep
entc
oef
ctrl
run 1
run 2
run 3
run 4
run 5
Random Parameters: Structural uncertainties due to subjective parameters (similitudes with QUMP)
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Stochastic Kinetic Energy Backscatter vn2.0 (SKEB2)
SKEB2 aims to address some of the issues related to model error, including:
• Excessive energy dissipation from smoothing in the semi-lagrangian advection schemes
• Missing feedback of kinetic energy from deep convection into the resolved flow
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Advection
+
Convection
Random pattern
SKEB2 increments u,v
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Example of decreased error of 500Z SKEB2 ensemble members (grey lines) compared to control (red-line)
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Concluding … GloSea4
• To become operational in August 09
• Preliminary results are promising
• Platform for model improvement (and testing of increased hor./vert. resolutions)
• Flexible system: easy to upgrade and allowing more frequent forecast updates
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How SKEB2 works (1):Calculate energy dissipation rates for numerical and convection schemes at each model time-step(shown here as an accumulation over a seasonal forecast)
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How SKEB2 works (2):Determine a streamfunction forcing field by merging the random pattern with the combined energy dissipation field. An example of the derived instantaneous wind increments are shown for horizontal/vertical slices, and zonal average
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Results
Various components of the seamless forecasting suite can benefit from backscatter schemes. Typically such schemes do require tuning, however some of the early results in the Unified Model N144 (1.25ox 0.83o) and N96 (1.875ox 1.25o) configurations are encouraging.
Improved skill and decreased systematic error in 500hPa geopotential height forecasts
Improved skill of ensemble mean when combined with ETKF initial perturbations in the 3-day MOGREPS suite
Increased internal variability in medium-range and seasonal forecasts
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30-day trial RMS-errors of ensemble mean 500Z forecasts (blue lines) for SKEB2 (dashed) and control (solid) (deterministic fcst shown in red)
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Increased variability of 10m wind-speed relative to time-mean for a seasonal forecast when including SKEB2
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Aims for SKEB
Models have an excessive dissipation of kinetic energy
Interpolation in semi-Lagrangian advection scheme
Limitations in the parameterisation scheme (e.g. Kinetic energy detrainment)
Stochastic Kinetic Energy Backscatter - Replenish excessively dissipated energy
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Stochastic Physics: SKEB2
SKEB2 = Stochastic Kinetic Energy Backscatter version 2
A randomly initialised stream-function forcing field (Ψ) is created with specified spatial and temporal characteristics
Calculate energy dissipation as a result of:
Numerical schemes: Smagorinsky-Lilly
Convection buoyancy: Mass-flux change * CAPE
Modulate the random Ψ-field with the energy dissipation
Calculate wind components from the Ψ-field and add to other wind increments from model physics at each time-step
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New system is better than old system!
GloSea4 is the first Met Office operational
system using HadGEM3
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GloSea4 timeline
•Aug 2009.- First GloSea4 operational seasonal forecast
2009 2010 2011N96L38 N96L85 N216L85
120km / low lid 120 km / strat. 50 km / stratos.
ORCA1L42 ORCA0.25L91
• 2011.- Seamless seasonal-to-(decadal?) system
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Concluding … Benefits of GloSea4
•Platform for model improvement for Seasonal-to-Decadal (and increased hor./vert. resolution)
• Flexible system that can be updated easily
• More frequent forecast updates (weekly)
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Improving HadGEM3 for S2D …
- Improved representation of physical processes (e.g. stratosphere, volcanoes)
- Increased resolution (e.g. atmospheric response to Atlantic SSTs)
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GloSea4 :Increasing model resolution
Components:
• UM atmosphere
• NEMO ocean
• CICE sea ice
• OASIS coupler GloSea4 is the first Met Office operational
system using HadGEM3
2009 2010 2011N96L38 N96L85 N216L85120km / low lid 120 km / strat. 50 km / stratos.
ORCA1L42 ORCA0.25L60
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Role of GloSea4 in MORPH3 to improve HadGEM3 for S2D …
- GloSea4 as a test-bed for model development
- GloSea4 as a flexible, easy-to-update system
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Nino 3 RMSE (lower=better)1989-1999
GloSea3 15-membersECMWF-S3 9-membersGloSea4 6-members
Similar spread betweenECMWF-S3 and GloSea4
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