1. New Saturation Adjustment for the COSMO model
Ulrich Blahak, Axel Seifert
German Weather Service, Offenbach
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

2. Motivation
Present saturation adjustment is formulated as an isobaric process and does not conserve mass.
During evaporation, mass is created and during condensation, mass is destroyed.
Because in total, there is more condensation than evaporation (due to precipitation), net sink of mass.
COSMO seems to be too dry compared to observations.
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

3. Saturation adjustment
x in kg/kg
T_0, x_v0, x_c0
T_adj, x_vadj, x_cadj
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

4. Saturation adjustment
Solution to achieve mass conservation during the process: Make it isochoric!
Implications: Change of thermodynamic formulation based on the first principle, adding pressure diagnosis after adjustment (→ let the model deal with the introduced pressure perturbation)
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

5. Isochoric saturation adjustment
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

6. Saturation adjustment
x in kg/kg
T_0, x_v0, x_c0
T_adj, x_vadj, x_cadj
adiab. expansion happening in the next timestep
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

7. Saturation adjustment
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

8. Testing idealized cases
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

9. Testing idealized cases
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

10. Testing idealized cases
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

11. Verification – COSMO EU June 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

12. Verification – COSMO EU June 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

13. Verification – COSMO EU June 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

14. Verification – COSMO EU June 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

15. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

16. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

17. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

18. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

19. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

20. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

21. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

22. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

23. Verification – COSMO DE Jul/Aug 2010
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,

24. Summary + Outlook
Isochoric saturation adjustment does conserve mass and seems to increase precipitation for both EU and DE.
Also influence on precipitation structure
Verification results so far indecisive: FBI improved, biases of T and p reduced, but other scores show no clear improvement.
Nevertheless, it will be more thoroughly tested in the framework of „65 levels for COSMO-DE“
Ulrich Blahak, DWD, COSMO General Meeting, Moskow,