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New Saturation Adjustment for the COSMO model

Ulrich Blahak, Axel Seifert German Weather Service, Offenbach. New Saturation Adjustment for the COSMO model. Motivation. Present saturation adjustment is formulated as an isobaric process and does not conserve mass.

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New Saturation Adjustment for the COSMO model

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

  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.

  3. Saturation adjustment T_0, x_v0, x_c0 x in kg/kg T_adj, x_vadj, x_cadj

  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)

  5. Isochoric saturation adjustment

  6. Saturation adjustment T_0, x_v0, x_c0 x in kg/kg T_adj, x_vadj, x_cadj adiab. expansion happening in the next timestep

  7. Saturation adjustment

  8. Testing idealized cases

  9. Testing idealized cases

  10. Testing idealized cases

  11. Verification – COSMO EU June 2010

  12. Verification – COSMO EU June 2010

  13. Verification – COSMO EU June 2010

  14. Verification – COSMO EU June 2010

  15. Verification – COSMO DE Jul/Aug 2010

  16. Verification – COSMO DE Jul/Aug 2010

  17. Verification – COSMO DE Jul/Aug 2010

  18. Verification – COSMO DE Jul/Aug 2010

  19. Verification – COSMO DE Jul/Aug 2010

  20. Verification – COSMO DE Jul/Aug 2010

  21. Verification – COSMO DE Jul/Aug 2010

  22. Verification – COSMO DE Jul/Aug 2010

  23. Verification – COSMO DE Jul/Aug 2010

  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“

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