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The status and development of the ECMWF forecast model

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The status and development of the ECMWF forecast model

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    1. The status and development of the ECMWF forecast model M. Hortal, M. Miller, C. Temperton, A. Untch, N. Wedi ECMWF

    2. Layout of the talk Continuous form of the equations Horizontal resolutions and spectral method Vertical resolution and vertical discretization Semi-Lagrangian scheme Efficiency Mass conservation and noise reduction Coupling with physics Future plans

    3. Continuous equations

    5. Horizontal resolutions in use at ECMWF TL511 for the deterministic forecast and outer loop of 4D-Var with a time step TL255 for EPS TL159 for inner loop of 4D-Var TL95 for seasonal forecast TL42 for error minimization computation TL799 used in some tests

    6. D+3 rainfall from a TL799 experiment

    7. Full and reduced Gaussian grids

    8. The quadratic and linear Gaussian grids

    9. Cost of various parts of the model at different horizontal resolutions

    10. Vertical resolutions used at ECMWF 60 levels for deterministic forecasts & 4D-Var (top at 0.1 hPa) 40 levels for EPS and seasonal forecasts (top at 10 hPa) 90 levels under test (top at 0.1 hPa)

    11. Vertical discretization In the semi-Lagrangian framework no vertical derivatives are needed Vertical integrals are computed with a finite-element method based on cubic B-splines Main benefits of finite-element scheme: no staggering of variables is required (advantage for semi-Lagrangian) reduction in vertical noise in the stratosphere significant reduction of a persistent cold bias in the lower stratosphere improved vertical transport ( => better conservation of ozone) smallest eigenvalues of the vertical modes are 10x larger than with the finite-difference method using the Lorenz staggering (facilitates use of PV as control variable in 4D-Var)

    14. Two-time-level semi-Lagrangian (SETTLS scheme)

    15. Efficiency of algorithms

    16. Continuity & thermodynamic equations

    17. Coupling of the dynamics with the physical parameterizations

    18. Validity of the present setup of the model Experience so far indicates that hydrostatic models give very similar results to non-hydrostatic ones at horizontal resolutions down to about 10 km The spectral transform method will remain affordable and competitive down to about 15 km Latitude-longitude grids allow easy coding of semi-Lagrangian advection schemes and communications in MPP’s

    19. Plans for the future Higher horizontal resolution TL1280 (~15 km) Higher vertical resolution L90 by 2003, L120 Reduction in cost of spectral transforms spherical harmonics double Fourier series Improvements to semi-Lagrangian scheme: improve interpolation (cubic spline for the vertical) add formal conservation properties Improve interfacing between dynamics and physics

    20. Plans for the future (cont.) Non-hydrostatic when the horizontal resolution approaches 10 km Relax the shallow-atmosphere approximation (coded for the IFS already by Meteo-France) Increase the degree of implicitness tests have been performed with a predictor-corrector method re-computation of the semi-Lagrangian trajectory in the corrector step improves the forecast skill scores, mainly at high horizontal resolution

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