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Page 1© Crown copyright 2004 SRNWP Lead Centre Report on Data Assimilation 2005 for EWGLAM/SRNWP Annual Meeting 2005 3-5 October 2005, Ljubljana, Slovenia Mike Bush NWP
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Page 2© Crown copyright 2004 1.SRNWP/Met Office/HIRLAM workshop in Exeter 2.Global model 4D-VAR 3.NAE model 4D-VAR 4.U.K 4km model 3D-VAR
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Page 3© Crown copyright 2004 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
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Page 4© Crown copyright 2004 1.SRNWP/Met Office/HIRLAM workshop in Exeter 2.Global model 4D-VAR 3.NAE model 4D-VAR 4.U.K 4km model 3D-VAR
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Page 5© Crown copyright 2004 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
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Page 6© Crown copyright 2004 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
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Page 7© Crown copyright 2004 Global 4D-VAR G33 5 th 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
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Page 8© Crown copyright 2004 PMSL NH T+24 RMS Error against analysis 8 4DVAR
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Page 9© Crown copyright 2004 500hPa Height SH T+24 RMS Error against analysis 9 4DVAR
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Page 10© Crown copyright 2004 250hPa Wind SH T+72 RMS Vector Error vs analysis 10 4DVAR
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Page 11© Crown copyright 2004 1.SRNWP/Met Office/HIRLAM workshop in Exeter 2.Global model 4D-VAR 3.NAE model 4D-VAR 4.U.K 4km model 3D-VAR
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Page 12© Crown copyright 2004 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
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Page 13© Crown copyright 2004 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
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Page 14© Crown copyright 2004 NAE 3D-VAR vs 4D-VAR PMSL Bias and RMSE 14
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Page 15© Crown copyright 2004 3D-VAR vs 4D-VAR Temperature Bias and RMSE 15
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Page 16© Crown copyright 2004 1.SRNWP/Met Office/HIRLAM workshop in Exeter 2.Global model 4D-VAR 3.NAE model 4D-VAR 4.U.K 4km model 3D-VAR
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Page 17© Crown copyright 2004 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
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Page 18© Crown copyright 2004 U.K 4km model 3D-VAR impact: PMSL
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Page 19© Crown copyright 2004 U.K 4km model 3D-VAR impact: 1.5m Temperature
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Page 20© Crown copyright 2004 U.K 4km model 3D-VAR impact: 10m wind
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Page 21© Crown copyright 2004 U.K 4km model 3D-VAR impact: cloud
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Page 22© Crown copyright 2004 Questions?
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