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© Crown copyright Met Office GloSea4: the new Met Office Seasonal Forecasting System A. Arribas, M. Glover, D. Peterson, A. Maidens, M. Gordon, C. MacLachlan,

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Presentation on theme: "© Crown copyright Met Office GloSea4: the new Met Office Seasonal Forecasting System A. Arribas, M. Glover, D. Peterson, A. Maidens, M. Gordon, C. MacLachlan,"— Presentation transcript:

1 © 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

2 © Crown copyright Met Office Working on this during the last two and a half years … due to become operational in August … Does it work?

3 © Crown copyright Met Office First ever GloSea4 forecast (initialised 25 th May)

4 © Crown copyright Met Office Nino3 SST RMSE (lower=better) 1989-1999 period GloSea315-members ECMWF-S3 9-members GloSea4 6-members

5 © Crown copyright Met Office 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

6 © Crown copyright Met Office GloSea3 vs. GloSea4 GloSea3 (current system)GloSea4 (new system) Model HadCM3 (N48L19 – 1/3L40) HadGEM3 (N96L38-ORCA1L42) Initialization Atmos/soil: ECMWF Ocean: UM-ocean 3D-OI Atmos/soil/sea-ice: Met Office Ocean: NEMO 3D-OI IC uncertainties Wind stress and SST perturbations added to a central analysis Weekly lagged approach Model uncertainties NoneRP + SKEB2 Forecast ensemble 41-members (monthly bursts from 1 st ) ~ 14 members per week Hindcast ensemble Run 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

7 © Crown copyright Met Office We’ve changed everything to … create a more flexible system, fully integrated with model development and better representing initial conditions and model uncertainties

8 © Crown copyright Met Office Current system (GloSea3) 1 st Jan 1991 Hindcast: Run apriori; 15 years; 15 members; 6-months forecasts Skill measurements Estimate mean errors to calibrate forecast 1 st Jan 1992 1 st Jan 2001 …………….. hindcast Expensive: A total of ~1350 years of simulations

9 © Crown copyright Met Office Current system (GloSea3) 1 st Jan 1991 Hindcast: Run apriori; 15-yrs (87-01); 15 members; 6-months forecasts Forecast: Run real-time; Monthly; 40 members; 6-months forecasts 1 st Jan 1992 1 st Jan 2001 …………….. 1 st Jan 2009 Skill measurements Estimate mean errors to calibrate forecast hindcast

10 © Crown copyright Met Office Problems with GloSea3: Decoupled from model development Not flexible: Difficult to upgrade model/system Only one forecast each month

11 © Crown copyright Met Office New system (GloSea4) 15 th Jan'09 22 th Jan'09 8 th Jan'09 1 st Jan'09 15 th Jan 22 th Jan 8 th Jan 1 st Jan 1989-2002 Assessment of skill and calibration on the fly Forecast Hindcast 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

12 © Crown copyright Met Office GloSea4 Forecast Suite Initial Conditions Calculation Post Processing Get NWP 4D VAR data Atmospheric reconfig. Ocean DA UM atmosphere NEMOCICE Archiving Skill & calibration Note: Data from Met Office NWP Note: ODA run daily (same as FOAM but different resolution)

13 © Crown copyright Met Office GloSea4 Hindcast Suite Initial Conditions Calculation Post Processing ERA-inter. Atmos. data Atmospheric reconfig. Ocean data UM atmosphere NEMOCICE Archiving Skill & calibration Note: Ocean data previously assimilated for all hindcast dates Note: Data from ECMWF reanalysis

14 © Crown copyright Met Office Flexible: easy to upgrade 200920102011 N96L38N96L85N216L85 120km / low lid 120 km / strat.50 km / stratos. ORCA1L42ORCA0.25L91 - Improved representation of physical processes (e.g. monsoon) from MORPH3 -Increased resolution

15 © Crown copyright Met Office 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

16 © Crown copyright Met Office GloSea4: Its role in HadGEM3 development obs HadGEM3 (climate bias) HadGEM3 (spin up) GloSea4 (HadGEM3 seasonal)

17 © Crown copyright Met Office Benefits of GloSea4: Linked to model development Easy to upgrade model/system Weekly forecast updates (seamless monthly system?)

18 © Crown copyright Met Office GloSea4 as an Ensemble Prediction System: representing uncertainties -Initial Conditions: Lagged approach -Model uncertainties: Stoch. Physics

19 © Crown copyright Met Office GloSea4 : Initial conditions Adding perturbations to a central analysis degrades the quality of the initial conditions ….

20 © Crown copyright Met Office Pert. Members CTRL (Bowler, Arribas and Mylne, 2008. MWR) GloSea4 : Problems adding perturbations to ICs

21 © Crown copyright Met Office 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

22 © Crown copyright Met Office 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

23 © Crown copyright Met Office Random Parameters: Structural uncertainties due to subjective parameters (similitudes with QUMP)

24 © Crown copyright Met Office 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

25 © Crown copyright Met Office Advection + Convection Random pattern SKEB2 increments u,v

26 © Crown copyright Met Office Example of decreased error of 500Z SKEB2 ensemble members (grey lines) compared to control (red-line)

27 © Crown copyright Met Office 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

28 © Crown copyright Met Office

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31 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)

32 © Crown copyright Met Office 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

33 © Crown copyright Met Office 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 (1.25 o x 0.83 o ) and N96 (1.875 o x 1.25 o ) 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

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

35 © Crown copyright Met Office Increased variability of 10m wind-speed relative to time-mean for a seasonal forecast when including SKEB2

36 © Crown copyright Met Office 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

37 © Crown copyright Met Office 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

38 © Crown copyright Met Office New system is better than old system! GloSea4 is the first Met Office operational system using HadGEM3

39 © Crown copyright Met Office GloSea4 timeline Aug 2009.- First GloSea4 operational seasonal forecast 200920102011 N96L38N96L85N216L85 120km / low lid 120 km / strat.50 km / stratos. ORCA1L42ORCA0.25L91 2011.- Seamless seasonal-to-(decadal?) system

40 © Crown copyright Met Office 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)

41 © Crown copyright Met Office

42 Improving HadGEM3 for S2D … -Improved representation of physical processes (e.g. stratosphere, volcanoes) -Increased resolution (e.g. atmospheric response to Atlantic SSTs)

43 © Crown copyright Met Office GloSea4 : Increasing model resolution Components: UM atmosphere NEMO ocean CICE sea ice OASIS coupler GloSea4 is the first Met Office operational system using HadGEM3 200920102011 N96L38N96L85N216L85 120km / low lid 120 km / strat.50 km / stratos. ORCA1L42 ORCA0.25L60

44 © Crown copyright Met Office 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

45 © Crown copyright Met Office Nino 3 RMSE (lower=better) 1989-1999 GloSea315-members ECMWF-S3 9-members GloSea4 6-members Similar spread between ECMWF-S3 and GloSea4

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