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SRNWP Lead Centre Report on Data Assimilation 2005 for EWGLAM/SRNWP Annual Meeting 2005

SRNWP Lead Centre Report on Data Assimilation 2005 for EWGLAM/SRNWP Annual Meeting 2005 3-5 October 2005, Ljubljana, Slovenia. Mike Bush NWP. SRNWP/Met Office/HIRLAM workshop in Exeter Global model 4D-VAR NAE model 4D-VAR U.K 4km model 3D-VAR. SRNWP/Met Office/HIRLAM Workshop.

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SRNWP Lead Centre Report on Data Assimilation 2005 for EWGLAM/SRNWP Annual Meeting 2005

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  1. SRNWP Lead Centre Report on Data Assimilation 2005 for EWGLAM/SRNWP Annual Meeting 2005 3-5 October 2005, Ljubljana, Slovenia Mike Bush NWP

  2. SRNWP/Met Office/HIRLAM workshop in Exeter • Global model 4D-VAR • NAE model 4D-VAR • U.K 4km model 3D-VAR

  3. SRNWP/Met Office/HIRLAM Workshop • Joint SRNWP/Met Office/HIRLAM Workshop on High resolution data assimilation: towards 1-4km resolution • Held at the Met Office, Exeter 15 -17 November 2004 • What is different for the convective scale? • High resolution observations – their assimilation & utility • Assimilating cloud and precipitation observations • Analysis techniques, 3D-Var and error covariances • 4D-Var issues

  4. SRNWP/Met Office/HIRLAM workshop in Exeter • Global model 4D-VAR • NAE model 4D-VAR • U.K 4km model 3D-VAR

  5. 4D-VAR: The Perturbation Forecast (PF) model • PF model is an approximation to the tangent linear model • Dynamical core: • Start from continuous equations • ECMWF start from the discrete equations for the dynamical core • scale analysis • Choose appropriate terms at an asymptotic limit • then discretize • Physics: • Simplified physics

  6. 4D-VAR : PF model physics • Simplified physics: • Boundary layer: friction and vertical diffusion of heat and momentum (following Buizza). • Latent heating scheme (simplified microphysics). • No convection. • No radiation. • No gravity wave drag

  7. Global 4D-VAR • G33 5th October 2004 • Introduction of 4D-VAR. • Single outer loop • Half model resolution (N108) • Positive benefit – greatest impact in the SH • Satellite data is asynoptic and so particularly suited to 4D-VAR

  8. PMSL NH T+24 RMS Error against analysis 4DVAR 4DVAR 8

  9. 500hPa Height SH T+24 RMS Error against analysis 4DVAR 9

  10. 250hPa Wind SH T+72 RMS Vector Error vs analysis 4DVAR 4DVAR 10

  11. SRNWP/Met Office/HIRLAM workshop in Exeter • Global model 4D-VAR • NAE model 4D-VAR • U.K 4km model 3D-VAR

  12. NAE 4D-VAR: how to treat the boundaries • Increments zero at the lateral boundaries • Weights of 0, 0, 0, 0, 0, 0.25, 0.5, 0.75 applied going away from the rim • Simple but cheap way of treating the boundaries • HIRLAM have a more sophisticated system using periodic boundaries • Only obs within ½ gridlength of the boundary are excluded

  13. NAE 4D-VAR testing • 2-week run at half-resolution was completed • Encouraging benefit to PMSL verification. • Other fields are more neutral/slight detriments. • Global 4DVAR does not assimilate screen level data, nor does it assimilate hourly sequences of the surface obs that it does use. • These new aspects of regional 4DVAR might need further tuning. • No problems with using persistence as the PF forecast for aerosol in the 2-week run • This means that experiments with visibility assimilation can go ahead

  14. NAE 3D-VAR vs 4D-VAR PMSL Bias and RMSE 14

  15. 3D-VAR vs 4D-VAR Temperature Bias and RMSE 15

  16. SRNWP/Met Office/HIRLAM workshop in Exeter • Global model 4D-VAR • NAE model 4D-VAR • U.K 4km model 3D-VAR

  17. U.K 4km model: 3D-VAR • Initial solution is to introduce 3D-VAR assimilation system (plus Analysis Correction scheme for cloud and precipitation) • So far 12 case studies run from June – September 2005 • Parallel Suite running scheduled for October 2005 • Implementation scheduled for November 2005 • Later upgrade will address consistency with larger scale increments from the driving model

  18. U.K 4km model 3D-VAR impact: PMSL

  19. U.K 4km model 3D-VAR impact: 1.5m Temperature

  20. U.K 4km model 3D-VAR impact: 10m wind

  21. U.K 4km model 3D-VAR impact: cloud

  22. Questions?

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