© Crown copyright Met Office GloSea4: the new Met Office Seasonal Forecasting System A. Arribas, M....

© Crown copyright Met Office

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


Working on this during the last two and a half years … due to become operational in August …

Does it work?


First ever GloSea4 forecast (initialised 25th May)


Nino3 SST RMSE (lower=better)

1989-1999 period

GloSea3 15-membersECMWF-S3 9-membersGloSea4 6-members


• 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


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


We’ve changed everything to …

create a more flexible system,

fully integrated with model development

and better representing initial conditions and model uncertainties


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


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


Problems with GloSea3:• Decoupled from model development

• Not flexible: Difficult to upgrade model/system

• Only one forecast each month


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


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)


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


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


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


GloSea4: Its role in HadGEM3 development

obs

HadGEM3 (climate bias)

HadGEM3 (spin up)

GloSea4 (HadGEM3 seasonal)


Benefits of GloSea4:• Linked to model development

• Easy to upgrade model/system

• Weekly forecast updates (seamless monthly system?)


GloSea4 as an Ensemble Prediction System:

representing uncertainties

- Initial Conditions: Lagged approach

- Model uncertainties: Stoch. Physics


GloSea4 : Initial conditions

Adding perturbations to a central analysis

degrades the quality of the initial conditions

….


Pert. Members

CTRL

(Bowler, Arribas and Mylne, 2008. MWR)

GloSea4 : Problems adding perturbations to ICs


• 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


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


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)


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


Advection

+

Convection

Random pattern

SKEB2 increments u,v


Example of decreased error of 500Z SKEB2 ensemble members (grey lines) compared to control (red-line)


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





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)


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


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


30-day trial RMS-errors of ensemble mean 500Z forecasts (blue lines) for SKEB2 (dashed) and control (solid) (deterministic fcst shown in red)


Increased variability of 10m wind-speed relative to time-mean for a seasonal forecast when including SKEB2


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


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


New system is better than old system!

GloSea4 is the first Met Office operational

system using HadGEM3


GloSea4 timeline

•Aug 2009.- First GloSea4 operational seasonal forecast

2009 2010 2011N96L38 N96L85 N216L85

120km / low lid 120 km / strat. 50 km / stratos.


• 2011.- Seamless seasonal-to-(decadal?) system


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)



Improving HadGEM3 for S2D …

- Improved representation of physical processes (e.g. stratosphere, volcanoes)

- Increased resolution (e.g. atmospheric response to Atlantic SSTs)


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.



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


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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