Nir Benmoshe, Alexander Khain Atmospheric science department The Hebrew University in Jerusalem

1. Aerosols effects on turbulence in mixed-phase deep convective clouds investigated with a 2D cloud model with spectral bin microphysicsThe 26th Annual Meeting of the Israeli Association of Aerosol Research Nir Benmoshe, Alexander Khain Atmospheric science department The Hebrew University in Jerusalem

2. HUCM • A 2D cloud model with 43 bins spectral bins • 7 different hydrometeors type • Aerosols • Diffusional growth, collision, freezing, melting, advection • Model resolution of 50 m x 50 m was used.

3. Droplet fall and collisions in non-turbulent air

4. Formation of eddies Relative velocities Absolute velocities

5. Physical mechanisms of effects of turbulence on collisions Formation of concentration inhomogeneity (droplet clustering) Formation of relative velocity between particles and environment

6. How does turbulence influence droplet collisions? is the collision kernel Swept volume Collision efficiency Fluctuations of concentration References: Saffman and Turner (1956); Khain and Pinsky, 1995; Pinsky and Khain, 1996,1997a,b; Pinsky et el, 2000, 2001; Zhou et al, 1998; Wang et al, 1998, 2000; Elperin and Dodin, 2012 References: Pinsky et al, 1999, 2000; 2001; 2004; 2008 Khain et al, 2000; Pigeonneau and Feuillebois, 2002 Wang et al, 2004; Ayala et al 2010 References: Maxey, 1987, Wang and Maxey, 1993; Pinsky et al. 1997; 1999, Pinsky and Khain 2001, 2003. Shaw et al, 1998; Shaw and Kostinsky 2003; Elperin et. al 1996; 1998, 2002 Falkovich et al, 2001, 2002; Benmoshe et al. (2012)combined effect of all factors

7. Collision kernel enhancement factors for different dissipation rates and Reynolds numbers Cumulonimbus Cumulus Stratocumulus Collision rate enhancement is determined by two parameters : eps and Re Mean normalized collision kernel in turbulent flow for three cases: stratiform clouds (left panel), cumulus clouds (middle) and cumulonimbus (right panel). Pressure is equal to 1000mb. (After Pinsky et al, 2008)

8. Novel approach for calculation of collisions: • Calculation of dissipation rate in each grid point at each time step • Calculation of Reynolds number in each grid point at each time step; • Calculation of collision enhancement factor in each grid point at each time step • This method makes it possible to investigate effects of turbulence on precipitation formation.

9. Calculation of dissipation rate Turbulence kinetic energy equation Dissipation rate cm^2/sec^3 Benmoshe et al. (2012)

10. Calculating L is the external turbulent scale Characteristic velocity fluctuation Taylor microscale Reynolds lambda Benmoshe et al. (2012)

11. CASE STUDIES: LBA-SMOC FIELD EXPERIMENT Andreae et al, 2004 • Blue ocean - CCN concentration 200 cm-3 • Green ocean – CCN concentration 700-900 cm-3 • Smoky clouds - CCN concentration 5000-10000 cm-3

12. Turbulent structure of deep cumulus clouds

13. Turbulence properties Benmoshe et al. (2012)

14. spatial vs. averaged values

15. Aerosols effect on cloud turbulence

16. Accumulated rain: effects of turbulence and aerosols

17. Effect of turbulence on collisions in mixed-phase clouds

18. The turbulence effect on ice particles collision is larger than on water droplets Nowell 2010 von Blohn et.al. 2005 Effects of turbulence on ice collisions should be larger because of lower sedimentation velocity at the same mass (inertia)

19. Increase in the collision kernel Pinsky, M.B., A.P. Khain, D. Rosenfeld and A. Pokrovsky, 1998

20. CONTROL EFFECTSWITH ENHANCED RIMING graupel graupel CWC CWC

21. CONTROL EFFECTSWITH ENHANCED RIMING Graupel, turb Graupel, grav Snow, turb Snow, grav

22. Accumulated rain

23. Conclusions – turbulence structure • High resolution of the model gives us real fractal cloud structures. • This is the first time that time and spatial depended turbulence characteristics were calculated for cumulus clouds • Turbulence in clouds is highly inhomogeneous: mean values do not reflect effects of turbulence on collisions • Turbulent intensity in clouds increase in the presence of higher aerosols concentration • Turbulence substantially accelerates formation of warm rain, especially in polluted clouds. • Increase in the collision rate between droplets reduces the total amount of precipitation since it eventually weakens cold precipitation processes • Turbulence in mixed phase clouds increases the rate of riming, mass and size of graupel and accelerates formation of cold rain

24. Questions ? Next time you are in an air pocket think about its good side….

25. Questions ?

26. IMPORTANCE OF THE STUDY • increasing the collision rate in highly turbulent clouds by order of the magnitude. • cloud turbulence determines processes of entrainment of dry air into the cloud and affects the cloud height. • The knowledge of the cloud turbulence intensity is important for purposes of flights safety. • why the shape of DSD is wider than it is supposed to be according to the equation for the diffusion droplet growth (e.g., Brenguier and Chaumat, 2001) • and why warm rain formation, as shown by Jonas (1996), occurs significantly faster than it is supposed to in accordance with the classical theory of gravitational coagulation. • Pinsky et al 2008 tell how turbulence kernel effect a DSD • Falkovich et al (2002); Pinsky et al (1997a,b; 2008); Xue et al (2008); Wang and Grabowsky (2009), the authors presented solutions of the stochastic collision equation in which turbulent effects on the evolution of the initially given DSD were simulated.

27. So, what are we talking about סרטון של ענן מצולם

28. Previous work • The mean kinetic energy dissipation rate in stratocumulus clouds (Sc) is estimated as (Siebert et al. 2006) and in small cumuli as (MacPherson and Isaac, 1977; Mazin et al 1989; Pinsky and Khain 2003). • According to Panchev (1971) and Weil et al (1993), the values of measured in deep cumulus clouds range from several hundreds to . • The recent measurements of the turbulent structure of the boundary layer using a helicopter (Siebert et al 2006) indicated dramatic spatial inhomogeneity of: while the typical mean values of are , in some zones of Sc clouds (possibly in zones of imbedded convection) the values of can increase up to . • the typical values of were estimated by Pinsky et al (2007, 2008) as ranging from ~ in stratiform clouds to ~in strong deep convective clouds (Cb). • According to Siebert et al (2006), turbulent intensity varies dramatically within stratocumulus clouds. One can expect a high variability of and in cumulus and Cb clouds as well. • To our knowledge, there have been no regular measurements of the fine spatial distribution of and in deep cumulus clouds. • Turbulence determines small scale spatial fluctuations of the liquid water content (e.g., Spyksma and Bartello, 2008). • turbulence affects droplet size distributions (DSD) thus having an impact on diffusion growth/evaporation of drops (e.g., Jensen and Baker, 1989; Khvorostyanov and Curry 1999a,b).

29. 3 3 3 RAIN DROP mass,1500sec,g/m RAIN DROP mass,1500sec,g/m RAIN DROP mass,1800sec,g/m 0.7 1.6 1.6 0.6 1.4 1.4 10.35 10.35 10.35 1.2 1.2 0.5 7.85 7.85 7.85 1 1 Height, km Height, km 0.4 Height, km 0.8 0.8 5.35 5.35 5.35 0.3 0.6 0.6 0.2 0.4 0.4 2.85 2.85 2.85 0.1 0.2 0.2 0.35 0.35 0.35 0 0 0 2.5 2.5 5 5 7.5 7.5 10 10 12.5 12.5 2.5 5 7.5 10 12.5 X, km X, km X, km 2 2 3 3 eps,1500sec,M eps,1500sec,M /S /S 2 2 3 3 eps,1800sec,M eps,1800sec,M /S /S 0.22 0.22 0.22 0.22 0.13 0.13 0.13 0.13 10.35 10.35 10.35 10.35 0.08 0.08 0.08 0.08 0.05 0.05 0.05 0.05 7.85 7.85 7.85 7.85 Height, km Height, km 0.03 0.03 Height, km Height, km 0.03 0.03 0.02 0.02 0.02 0.02 5.35 5.35 5.35 5.35 0.01 0.01 0.01 0.01 2.85 2.85 0.00 0.00 2.85 2.85 0.00 0.00 0.00 0.00 0.00 0.00 0.35 0.35 0.35 0.35 0.00 0.00 2.5 2.5 5 5 7.5 7.5 10 10 12.5 12.5 2.5 2.5 5 5 7.5 7.5 10 10 12.5 12.5 X, km X, km X, km X, km Where are the first drops forms? E200T E2000T Rain water content, gm Rain water content, gm , t=1500s , t=1500s - - 3 3 Rain water content, gm Rain water content, gm , t=1800s , t=1800s - - 3 3 Dissipation rate, m Dissipation rate, m s s , t=1500s , t=1500s 2 2 - - 3 3 Dissipation rate, m Dissipation rate, m s s , t=1800s , t=1800s 2 2 - - 3 3

30. Data Size Distributions

31. How is the first precipitation influenced by turbulence ? GO-turb Strange notations GO-grav S-grav S-turb

32. Reff