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A. Walser 1) M. Arpagaus 1) M. Leutbecher 2) 1) MeteoSwiss, Zurich 2) ECMWF, Reading, GB

The impact of moist singular vectors and ensemble size on predicted storm tracks for the winter storms Lothar and Martin. A. Walser 1) M. Arpagaus 1) M. Leutbecher 2) 1) MeteoSwiss, Zurich 2) ECMWF, Reading, GB. Storms Lothar & Martin.

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A. Walser 1) M. Arpagaus 1) M. Leutbecher 2) 1) MeteoSwiss, Zurich 2) ECMWF, Reading, GB

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  1. The impact of moist singular vectors and ensemble size on predicted storm tracks for the winter storms Lothar and Martin A. Walser1) M. Arpagaus1) M. Leutbecher2) 1)MeteoSwiss, Zurich 2)ECMWF, Reading, GB

  2. Storms Lothar & Martin • Occurred on 24 Dec (Lothar) and 26/27 Dec 1999 (Martin) in Central Europe • At least 80 casualties • Economic losses of ~18 billions USD • Not predicted by the national weather services →Motivation for the study: Improvement of early warnings for such extreme weather events

  3. Ensemble forecasts • Initial perturbations should match the uncertainties in the initial conditions. • Ideally, an ensemble span the entire range of possible solutions.

  4. Ensemble forecasts • Initial perturbations should match the uncertainties in the initial conditions. • Ideally, an ensemble span the entire range of possible solutions. • Initial perturbations using “moist” singular vectors (SVs) might lead to a more reliable spread for short lead-times.

  5. Moist vs. operational singular vectorsCoutinho et al. (2004) • ‚opr‘ SVs (T42L31, OT 48 h): linearized physics package with • surface drag • simple vertical diffusion • ‚moist‘ SVs (T63L31, OT 24 h): linearized physics package includes additionally: • gravity wave drag • long-wave radiation • deep cumulus convection • large-scale condensation

  6. dynamical downscaling Ensemble strategy Variant of the operational COSMO-LEPS: Limited-area ensemble Global ensemble • Lokal Modell with x~10 km and 32 levels • 72-h forecasts • 51 members LM, x~10 km ECMWF, ∆x~80 km, opr/moist SVs

  7. Ensemble simulations • Storm Lothar: 26 December 1999 • moist SVs ensembles, 19991224 00 UTC, + 72 h • opr SVs ensembles, 19991224 00 UTC, + 72 h • Storm Martin: 27/28 December 1999 • moist SVs ensembles, 19991226 00 UTC, + 72 h • opr SVs ensembles,19991226 00 UTC, + 72 h • LM 3.9 ensembles: • ∆x ~10 km (as COSMO-LEPS)

  8. “Pronounced” storm track In the forecast range considered: • Minimum sea level pressure of 980 hPa. • At least 1000 km west-east elongation. • For each ensemble member, the track with the earliest and southernmost starting point of the tracks which fulfill 1) and 2) is considered.

  9. Lothar: Predicted storm tracks t+(42-66) < 980 hPa (1) ensemble members: 32 tracks ▬analysis • Impact of perturbations • Configuration: • dry SVs/51 RMs • moist SVs/51 RMs < 970 hPa < 960 hPa

  10. Lothar: Predicted storm tracks t+(42-66) < 980 hPa (2) ensemble members: 36 tracks ▬analysis • Impact of perturbations • Configuration: • dry SVs/51 RMs • moist SVs/51 RMs < 970 hPa < 960 hPa

  11. Martin: Predicted storm tracks t+(42-66) < 980 hPa (1)  ensemble members: 2 tracks ▬analysis • Impact of perturbations • Configuration: • dry SVs/51 RMs • moist SVs/51 RMs < 970 hPa < 960 hPa

  12. Martin: Predicted storm tracks t+(42-66) < 980 hPa (2) ensemble members: 12 tracks ▬analysis • Impact of perturbations • Configuration: • dry SVs/51 RMs • moist SVs/51 RMs < 970 hPa < 960 hPa

  13. Impact of ensemble size

  14. Lothar: Predicted storm tracks t+(42-66) < 980 hPa ensemble members: 36 tracks (71%) ▬analysis • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs < 970 hPa < 960 hPa

  15. Lothar: Predicted storm tracks t+(42-66) < 980 hPa ensemble members: 14 tracks (70%) ▬analysis • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs < 970 hPa < 960 hPa

  16. Lothar: Predicted storm tracks t+(42-66) < 980 hPa ensemble members: 7 tracks (70%) ▬analysis • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs < 970 hPa < 960 hPa

  17. Lothar: Predicted storm tracks t+(42-66) < 980 hPa ensemble members: 4 tracks (80%) ▬analysis • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs < 970 hPa < 960 hPa

  18. Forecast storm Lothar: max. wind gusts t+(42-66) (1) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  19. Forecast storm Lothar: max. wind gusts t+(42-66) (2) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  20. Forecast storm Lothar: max. wind gusts t+(42-66) (3) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  21. Forecast storm Lothar: max. wind gusts t+(42-66) (4) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  22. Forecast storm Martin: max. wind gusts t+(30-54) (1) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  23. Forecast storm Martin: max. wind gusts t+(30-54) (2) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  24. Forecast storm Martin: max. wind gusts t+(30-54) (3) moist SVs, x~10 km, 10 members • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  25. Forecast storm Martin: max. wind gusts t+(30-54) (4) • Impact of ensemble size • Configuration: • moist SVs/51 RMs • moist SVs/20 RMs • moist SVs/10 RMs • moist SVs/5 RMs

  26. Summary • Use of moist SVs leads to a larger number of members with a storm track similar to the observed one. • Potential for earlier warnings • However, consequence for false alarm rate unknown • Ensemble reduction method of COSMO-LEPS works well. 10 RMs seems to be a good compromise between required computing resources and forecast accuracy.

  27. Extra Slides

  28. Wind gusts storm Martin (27.-28.12.1999) LM analysis with nudging: Proxy for observations “Brasseur (2001) wind gusts”

  29. Wind gusts storm Lothar (26.12.1999) LM analysis with nudging: Proxy for observations “Brasseur (2001) wind gusts”

  30. Parameterization for 10m wind gusts • LM („operational“): • 3 x double turbulent kinetic energy in Prandtl-Layer: • U* : Friction velocity • Brasseur wind gust formulation • (Mon. Wea. Rev. 129, 5-25, 2001)

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