1. Perturbation of Parametrized Tendencies and Surface Parameters in the Lokal-Modell Susanne Theis Andreas Hense Ulrich Damrath Volker Renner

2. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion The LAM “Lokal-Modell“ operational high-resolution model of the DWD nested within the GME horizontal gridsize: 7 km lead time: 48 hours

3. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Why are we looking into EPS? DMO of a single simulation noise-reduced forecast and probabilistic forecast Development of a Postprocessing Method:

4. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Why are we looking into EPS? DMO of a single simulation noise-reduced forecast and probabilistic forecast Development of a Postprocessing Method: calibration by an experimental ensemble

5. uncertainty in lateral boundary conditions OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Aims of a LAM EPS model uncertainty uncertainty in surface parameters uncertainty in LAM output ? uncertainty in initial conditions

6. uncertainty in lateral boundary conditions OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Selecting Certain Aspects model uncertainty uncertainty in surface parameters uncertainty in LAM output ? uncertainty in initial conditions

7. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Perturbation of Roughness Length originalperturbation m m

8. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Perturbation of Roughness Length where = 0 STDV 0.05 E and Set-up of the ensemble (6 members):

9. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Case Study (July 4th, 1994) mm/h Ensemble Mean Standard Deviation perturbation of roughness length (only)

10. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion „Stochastic Physics“: Method Perturbation of parametrized tendencies: Unperturbed simulation: Ensemble member: (Buizza et al, 1999)

11. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion „Stochastic Physics“: Numerics Caveat: Stochastic differential equations need a different numerical scheme (Kloeden and Platen, 1999) -- we are still using the traditional scheme!

12. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Consistency with Surface Radiation Perturbation of the temperature tendency should be consistent with the solar radiation flux at the surface: z Q z Q perturbation of tendency

13. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion „Stochastic Physics“: Set-up No.1 D = 5 T = 4 x t „low ampl.“ Set-up of the ensemble (10 members): consistent perturbation of the solar radiation at the surface +

14. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Roughness Length where = 0 STDV 0.05 E and Additionally, we keep the perturbation of the roughness length:

15. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Roughness Length: The Bug where = 0 STDV 0.05 E and roughness length is too low (by a factor of 6) SORRY

16. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Case Study (July 10th, 2002) mm/h Ensemble Mean Standard Deviation stochastic physics (low-amplitude)

17. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Verification of Ensemble Mean ENSMEAN ORIGINAL stochastic physics (low-amplitude)

18. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion „Stochastic Physics“: Set-up No.2 D = 10 T = 16 x t „high amplitude“ Set-up of the ensemble (10 members): consistent perturbation of the solar radiation at the surface +

19. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Case Study (July 10th, 2002) mm/h Ensemble Mean Standard Deviation stochastic physics (high-amplitude)

20. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Verification of Ensemble Mean ENSMEAN ORIGINAL stochastic physics (high-amplitude)

21. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Perturbation of Initial Conditions Start of the LM-Simulations: 00 UTC Initialize LM-simulation with the „wrong“ time of the nudged assimilation run: Analysis of 01 UTC Analysis of 00 UTC Analysis of 23 UTC (prev.day)

22. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Set-up of the Ensemble D = 5 T = 4 x t „low ampl.“ consistent perturbation of the solar radiation at the surface + Additionally, the parametrized tendencies are perturbed:

23. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Set-up of the Ensemble Analysis of 01 UTC Analysis of 00 UTC Analysis of 23 UTC (prev.day) 3 simulations per analysis + 1 unperturbed simulation = 10 ensemble members 3 simulations

24. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Case Study (July 10th, 2002) mm/h Ensemble Mean Standard Deviation initial conditions & stochastic physics (low-amplitude)

25. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Verification of Ensemble Mean ENSMEAN ORIGINAL ínitial conditions & stochastic physics (low-amplitude)

26. OUTLINE Introduction Surface Parameters Parametrized Tendencies Initial Conditions Conclusion Conclusion the precipitation forecast is sensitive to the perturbation of roughness length, parametrized tendencies and initial conditions the sensitivity is largest on the scale of a few gridboxes in size the ensemble mean achieves better verification results than the unperturbed forecast (initial cond.!)