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Parameterization of precipitation in boundary layer clouds at the cloud system scale

Parameterization of precipitation in boundary layer clouds at the cloud system scale. Olivier Geoffroy. Pier Siebesma, Roel Neggers. RK science lunch, 05/10/2010. Microphysical processes. Cloud droplets : ~ 1 µm < D < ~ 40 µm. CCN : D ~ 0.01-10 µm. CCN Activation. n(D). w. D.

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Parameterization of precipitation in boundary layer clouds at the cloud system scale

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  1. Parameterization of precipitation in boundary layer clouds at the cloud system scale Olivier Geoffroy Pier Siebesma, Roel Neggers RK science lunch, 05/10/2010

  2. Microphysical processes Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm CCN Activation n(D) w D 40 µm

  3. Microphysical processes Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Condensation n(D) D 40 µm CCN Activation n(D) w D 40 µm

  4. Microphysical processes Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) D 40 µm Condensation n(D) D 40 µm CCN Activation n(D) w D 40 µm

  5. Microphysical processes Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Condensation n(D) D 40 µm CCN Activation n(D) w D 40 µm

  6. Collection n(D) D 40 µm Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Condensation ECS n(D) D 40 µm Collection : Efficient for D > 40 µm (Bartlett, 1970) CCN Activation n(D) w D 40 µm

  7. Collection n(D) D 40 µm Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Condensation ECS n(D) D 40 µm Collection : Efficient for D > 40 µm (Bartlett, 1970) CCN Activation n(D) Polluted cloud • precipitation efficiency (?) • LWP (?(feedbacks)) w D (2nd aerosol indirect effect) 40 µm

  8. Microphysical processes Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Condensation n(D) D 40 µm CCN Activation n(D) w Marine cloud D 40 µm

  9. Collection n(D) D 40 µm Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Condensation ECS n(D) D 40 µm Collection : Efficient for D > 40 µm (Bartlett, 1970) CCN Activation n(D) w D 40 µm

  10. Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm Rain drops ~ 40 µm <D < 100-500 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Collection Condensation n(D) ECS n(D) D 40 µm D 40 µm CCN Activation Growth depends on the available amount of water i.e. H or LWP n(D) w D 40 µm

  11. Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm Rain drops ~ 40 µm <D < 100-500 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Collection Condensation n(D) ECS n(D) D 40 µm D 40 µm Rain sedimentation CCN Activation n(D) w D 40 µm

  12. Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm Rain drops ~ 40 µm <D < 100-500 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Collection Condensation n(D) ECS n(D) D 40 µm D 40 µm Rain sedimentation size sorting CCN Activation n(D) Rain evaporation D 40 µm

  13. Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm Rain drops ~ 40 µm <D < 100-500 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Collection Condensation n(D) ECS n(D) D 40 µm D 40 µm Rain sedimentation size sorting CCN Activation n(D) Rain evaporation D 40 µm

  14. Microphysical processes precipitation embryo D ~ 40 µm Cloud droplets : ~ 1 µm < D < ~ 40 µm Rain drops ~ 40 µm <D < 100-500 µm CCN : D ~ 0.01-10 µm Mixing n(D) Cloud droplet sedimentation D 40 µm Collection Condensation n(D) ECS n(D) D 40 µm D 40 µm Rain sedimentation size sorting CCN Activation n(D) Rain evaporation D 40 µm

  15. Objective • Development of a precipitation scheme for boundary layer clouds at the GCM scale • Precipitation in a key process in BLC evolution. • Low cloud regimes and transitions between regimes Earth radiation budget, general circulation, hydrological cycle.  Quantification of the aerosol indirect effect.

  16. LES collection schemes Measured spectra Bulk Cloud n(D) Cloud rain rain D D0 D0 ~ 40 - 100 µm 2 bins  4 collectionprocesses D (μm) explicit or bin Autoconversion Cloud Rain: qr (g kg-1) Nr(cm-3) Cloud : qc(g kg-1) Nc (cm-3) n(D) rain Accretion D Self-collection Self-collection D0 Collection processes : Stochastic Collection Equation (SCE)

  17. Precipitation formation, autoconversion rate Autoconversion Rain: qr (g kg-1) Nr(cm-3) Cloud : qc(g kg-1) Nc (cm-3) Accretion Naerosol Auto rate Nc α β Treshold Nc 1 H(qc-qtreshold) 0 Kessler (1969) qc 1 0 Sundqvist (1978) 2.47 -1.79 Khairoutdinov and Kogan (2000) 1 Highly non linear 4.7 -3.3 1 Beheng (1994) Depends on local values 4 -2 Seifert and Beheng (2001) 1 H(rv-rvtreshold) 2.33 -0.33 Tripoli and Cotton (2000) Aerosol indirect effect dependance in Nc necessary H(r6-rtreshold) 2.33 -0.33 Liu and Daum (2006)

  18. Autoconversion / accretion rates mean profiles (12H) in cumulus auto accr Only in cloud core • - Formation of precipitation in cloud core • Accretion = • ~ 10 x autoconversion Only in cloud core accr wup-vqr > 0 vqr • Simulations show larger accretion rate for wup-vqr > 0 • (drops go upward) wup wup-vqr < 0

  19. 0 overlap, Sundqvist (1978) scheme Autoconversion: qc=lup(k) w=wup(k-1) Frac=cste =cste?

  20. New scheme Autoconversion: qc=lup(k) w=wup(k-1) Frac=cste

  21. New scheme, accretion regime Accretion: (From RICO in situ measurements) Frac=cste

  22. New scheme,overlap ho ? k+1 ztop k zk Frac=cste

  23. Autoconversion formulation Horizontal mean values of: • LES simulations (12H) • RICO, moister RICO • Nc= 40, 50, 70, 100, 200cm-3 • Seifert and Beheng (2006) • scheme: Identification of individual clouds and average clouds of same height autoLES = f(autoparam) power law hypothesis: 1/1 line (kg kg-1 s-1) & regression (kg kg-1 s-1)

  24. SCM results

  25. LWP, rain flux at surface, Nc=50, 70, 100, 200 cm-3 No rain LWP: 200 cm-3 60 g m-2 70 cm-3 100 cm-3 50 cm-3 precipitation at surface: = 25 Wm-2 ~ 0.4 mm h-1 ~ 10 mm j-1 50 cm-3 100 cm-3 70 cm-3 200 cm-3

  26. rain flux profilesNc=50, 200 cm-3 Nc = 50 cm-3 Nc = 200 cm-3

  27. Autoconversion time scale w=wup w=5ms-1 w=1ms-1 w=5ms-1 w=1ms-1 w=wup

  28. Sensitivity to the overlap LWP h0=300 Nc = 50 cm-3 h0=600 h0=1000 h0=1000 h0=600 h0=300

  29. Conclusion and perpective • Developpment and implementation of a precipitation scheme in ECMWF SCM model coupled with the DualM scheme. • Possibility to take in account the shear effect • - Possible to take in account interaction between precipitation flux and the stratiform component of the cloud (for Sc). • Dependency in NCCN • Test of the scheme using the KPT and half a year of precipitation flux and CCN concentration measurements: Dust episode Regional background Regional background North Sea origins CCN concentration at Cabauw during IMPACT (May 2008)

  30. Sundqvist no evap SB, no evap, Nc 70 lwp lwp Rsurf Rsurf

  31. Sundqvist no evap SB, no evap, Nc 50 lwp lwp Rsurf Rsurf

  32. SB, evap2, Nc 200 SB, evap2, Nc 70 lwp lwp Rsurf Rsurf Rsurf

  33. h0=300, 500, 800, 1500, SB, Nc 50, evap2 lwp lwp h0 300 m h0 500 m lwp lwp h0 800 m h0 1500 m

  34. lwp SB, Nc 50, original evap auto2, Nc 50, original evap auto2, Nc 50, evap2

  35. SB, evap2, Nc 50 lwp Rsurf

  36. auto 2 (a=2.74, b=-1.35) lwp lwp Nc 50 cm-3 Nc 70 cm-3 lwp Nc 200 cm-3

  37. bNc=1.17 Param accr up + auto aqr=1.85 w0=5 ms-1 10e-6

  38. Param accr up + auto w0=5 ms-1 2.5e-6

  39. LWP, rain flux at surface, Nc=50, 70, 100, 200 cm-3 No rain LWP: 200 cm-3 60 g m-2 70 cm-3 100 cm-3 50 cm-3 precipitation at surface: = 25 Wm-2 ~ 0.4 mm h-1 ~ 10 mm j-1 50 cm-3 100 cm-3 70 cm-3 5 Wm-2 200 cm-3

  40. Steady state:

  41. wup-vqr < 0 wup-vqr > 0

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