AM2 cloud sensitivity to details of convection and cloud paramerization – the GPCI case

1. AM2 cloud sensitivity to details of convection and cloud paramerization – the GPCI case Ming Zhao GFDL / Princeton University September 18-21, 2006 Joint GCSS-GPCI / BLCL - RICO Workshop

2. Outline • AM2 cloud and convection parameterization • Experiments • Results • Summary

3. AM2 cloud and convection parameterization Tiedtke prognostic cloud scheme

4. Relaxed Arakawa-Schubert (RAS) convection scheme Cloud model: • Ensemble entraining plumes with each entrainment rate calculated so that it reaches a model level with neutral buoyancy • Non-entraining plumes • Tokioka entrainment rate limiter • Applying Tokioka limiter only to deep plumes above 500 hPa • Local modification of critical cloud work function Closure: • Relax plume cloud work function to specified critical values with specified time-scale.

5. UW shallow cumulus scheme (Bretherton et. al 2004) Cloud model: • Bulk entrainment-detrainment plume • Buoyancy-sorting determination of entrainment/detrainment rate • Explicit vertical momentum equation • Cumulus cloud-top penetrative mixing Closure: • Cloud-base mass flux is determined by boundary layer TKE and convective inhibition (CIN).

6. Experiments (GPCI 1998) • CNTRL : AM2 default with FV dynamic core • NOSHA: Same as CNTRL except disallowing RAS plumes below 500hPa • NONON: Same as CNTRL except applying Tokioka to all RAS plumes (eliminating non-entraining plume) • UWSCU: Same as NONON except applying UW-ShCu before RAS, and disallowing RAS plumes below UW-ShCu calculated convective depth H

7. Results

8. Liquid water path

9. SW absorption at TOA

10. Cloud fraction

11. Cloud liquid (g/kg)

12. Cloud liquid water tendencies from convection (g/kg/day)

13. Cloud liquid water tendencies from large-scale condensation (g/kg/day)

14. Large-scale/stratiform precipitation

15. Specific humidity tendencies from convection (g/kg/day)

16. Relative humidity

17. Convective mass flux (kg/m2/s)

18. NOGMC case

19. CNTRL vs. NOGMC

20. CNTRL vs NOGMC

21. Summary • Tropical low cloud fraction and condensate are susceptible to the detailed treatment of shallow convection. Weaker shallow convection leads to large increase of low clouds. • Budget analysis show that the increase of low clouds is due to increased large-scale condensation instead of convective detrainment. • Sensitivity study show that wetter lower troposphere and reduced compensating subsidence resulting from weaker shallow convection are two primary causes.

22. End

26. Total precipitation

28. Cloud fraction tendencies from convection (1/day)

29. Cloud fraction tendencies from large-scale formation (1/day)

30. Cloud fraction tendencies from turbulent erosion (1/day)

31. Cloud liquid tendencies from large-scale evaporation (g/kg/day)

32. Cloud liquid tendencies from turbulent erosion (g/kg/day)

33. Cloud liquid tendencies from microphysics (g/kg/day)

34. Vertical pressure velocity (hPa/day)

35. Summary • Tropical low cloud fraction and condensate are susceptible to the detailed treatment of shallow convection. Weaker shallow convection leads to large increase of low clouds. • Budget analysis show that the increase of low clouds is due to large-scale condensation instead of convective detrainment. • Budget analysis and sensitivity study show that wetter lower troposphere and reduced compensating subsidence resulting from weaker shallow convection are two primary causes.

36. Sub-cloud TKE virtual potential temperature 0 1 fraction of environmental air Sub-cloud layer TKE and cloud detrainment Cloud detrainment

37. Steady state solution for the dominant balance cloud liquid cloud fraction depend on entrainment rate steady state solution depend on both entrainment rate and cloud-base mass flux / cloud work function