COSMO implementations at CNMCA: tests with different dinamycal options

1. COSMO implementations at CNMCA: tests with different dinamycal options Lucio TORRISI Italian Met. Service CNMCA – Pratica di Mare (Rome) l.torrisi@meteoam.it

2. Overview • COSMO implementations at CNMCA • New reference atmosphere impact • 7km RK/LF comparison • RKold (previous to 4.9) • RK4.9 • RK4.9_EVA • MSLP bias distribution • 14 km RK4.9_EVA/LF comparison • 2.8 km RKold/RKold_EVA comparison • Conclusion

3. CNMCA NWP System • compressible equations • explicit convection 2.8 km • hydrostatic equations • parameterized convection 14 km • compressible equations • parameterized convection 7 km

4. New reference atmosphere Zaengl (2008) implemented in COSMO model a new reference atmosphere based on a temperature profile which starts with a prescribed sea-level temperature and exponentially approaches an isothermal stratosphere. In this way there is no limitation on vertical extent of model domain.

5. New reference atmosphere

6. Pressure bias problem (1) • This problem was pointed out in Torrisi (2005): “Sensitivity experiments with the Runge Kutta time integration scheme”, presentation at COSMO GM in Zurich 1) RK/LF core - Objective verification showed a difference in MSLP bias behaviour between 7km RK (red line) and LF (green line)runs. MSLP bias difference increases with forecast time. RK runs have a larger bias, typically positive, leading to a worse RMSE.

7. 7km RKold/LF comparison

8. 7km RKold/LF comparison

9. 7km LF: MSLP bias

10. 7km LF/RKold: MSLP bias

11. 7km RK4.9/LF comparison In COSMO 4.9 a more accurate discretization of the metric terms was introduced by G. Zaengl.

12. 7km RK4.9/LF comparison

13. 7km RK4.9/LF comparison

14. 7km RK4.9/LF comparison

15. 7km RK4.9/LF comparison

16. 7km LF/RK: MSLP bias LF RK4.9 RKold

17. 14km RK4.9/LF comparison

18. RK/LF comparison • Pressure forecast skill of RK dynamical core was clearly improved by the new discretization of the metric terms introduced in version 4.9 (7-14km) • RK have a better MSLP RMSE than LF; the sign of bias is positive for LF and negative for RK • Spatial distribution of RK MSLP bias confirms how this dynamical core is sensitive to the change in the discretization of the metric terms.

19. RK4.9 IVA/EVA comparison Vertical advection in COSMO • IVA - Vertically implicit centered diff. 2° order (and 3° order in the next future) • EVA - Vertically explicit upwind scheme (3°/5° order)

20. 7km RK4.9 IVA/EVA comparison

21. 7km RK4.9 IVA/EVA comparison

22. 7km RK4.9 IVA/EVA comparison

23. 7km RK4.9 IVA/EVA comparison

24. 2.8km RK4.9 IVA/EVA compar.

25. Conclusion • The new reference atmosfere has a neutral impact except for above 100 hPa. • The pressure forecast skill of RK dynamical core is clearly improved by the new discretization of the metric terms introduced in version 4.9 (7-14km) • The third order explicit vertical advection scheme has a slightly positive impact on wind and mean sea level pressure (higher accuracy, more consistent with explicit horizontal advection).

26. Thank you for your attention!

27. Pressure bias problem (2) 2) Domain size - Objective verification showed a difference in MSLP bias behaviour in 7km RK (and LF) runs having a different domain size (smaller one - red line, larger one -green line). The larger domain, the greater MSLP bias

28. Pressure bias problem (3) 3) Model formulation - Objective verification showed a difference in MSLP bias behaviour between 14km COSMO LF/RK (blue line) and HRM (red line) runs. HRM is the DWD regional hydrostatic model (LF time integration scheme) used in the CNMCA assimilation systems (3D-Var PSAS and LETKF). MSLP bias difference increases with forecast time (COSMO larger positive bias) COSMO EURO-HRM