1. SIMULATION OF AEROSOL EFFECTS ON CONVECTIVE CLOUDS UNDER CONTINENTAL AND MARITIME CONDITIONS Alexander Khain, Andrei Pokrovsky and Daniel Rosenfeld Institute of Earth Sciences The Hebrew University of Jerusalem Email: Khain@vms.huji.ac.il

2. f water (m) 0.5 cm f col (m) f plate (m) f dend (m) f snow (m) 3 cm f graup (m) 0.8 cm f hail (m) 0.6 cm SIZE DISTRIBUTION FUNCTIONS IN THE HUCM Radii of particles f aeros (m)

3. Microphysical processes in HUCM supersaturation ICE MULTIPLICATION RAIN CCN budget ICE PRECIPITATION NUCLEATION OF DROPLETS AND ICE CRYSTALS DROP-DROP, DROP-ICE and ICE-ICE COLLISIONS MELTING OF ICE DIFFUSIONAL GROWTH/ EVAPORATION OF DROPLETS DEPOSITION / SUBLIMATION OF ICE BREAKUP OF DROPLETS SEDIMENTATION OF PARTICLES Updraft, supersaturation FREEZING OF WATER DROPS supersaturation

4. CCN BUDGET AND PROCESS OF DROPLET NUCLEATION

5. Simulation of extremely continental clouds (Texas, August 1999)

6. TEXAS: aerosol effects on precipitation formation

7. Clean air (maritime aerosol) TEXAS: rain rate Depletion of rain in smoky air Smoky air (continental aerosol)

8. TEXAS: rain accumulation Depletion of rain in smoky air

9. CONCLUSION 1: An increase in CCN concentration leads to DEPLETION of precipitation under dry and unstable continental conditions.

10. Simulation of deep tropical convection OVER THE SEA (GATE, Day 261)

11. Clean air (maritime aerosol) Smoky air (continental aerosol) Increase in rain in smoky air New clouds appear GATE, Day 261: Precipitation rate

12. Accumulated rain GATE, Day 261TEXAS Rain increase Rain decrease

13. WHY INCREASE IN CCN CONCENTRATION CAN LEAD TO RAIN INCREASE ? EFFECT OF AEROSOLS ON CLOUD DYNAMICS

14. GATE, Day 261: Vertical velocities Clean air (maritime aerosol) Smoky air (continental aerosol)

15. GATE, Day 261: Development of new clouds Clean air (maritime aerosol) Smoky air (continental aerosol) New cloud develops New cloud doesn’t develop

16. GATE, Day 261: Evolution of CCN concentration Clean air (maritime aerosol)Smoky air (continental aerosol)

17. Simulation of PRESTORM squall line OVER THE LAND

18. PRESTORM: Time evolution of radar reflectivity Clear air (Maritime) Smoky air (Continental) Squall line develops ! No squall line !

19. Prestorm: Time evolution of aerosol concentration Clear air (Maritime)Smoky air (Continental) Squall line

20. Prestorm: Time evolution of rain rate Clear air (Maritime)Smoky air (Continental) Old cloud No development Squall line

21. Prestorm: Time evolution of accumulated rain Squall line forms in smoky air ! No squall line forms in clean air !

22. Scheme of aerosol effects on precipitation Aerosol concentration Dry unstable situation (like Texas clouds) Maritime & moderate (wet) continental clouds (like GATE and PRESTORM) Accumulated rain

23. It is found that aerosols crucially affect precipitation. HOWEVER: Effect of aerosols is ambiguous: a)An increase in CCN concentration leads to DEPLETION of precipitation under dry and unstable continental conditions. b)An increase in CCN concentration leads to INCREASE in precipitation under maritime and moderate continental conditions. c)Aerosols crucially affect cloud dynamics and formation of cloud clusters and squall lines. d)Therefore CCN budget significantly affects convective activity. CONCLUSIONS

24. The End

25. THE ROLE OF AEROSOL BUDGET SIMULATIONS a) WITH “SPECTRAL-BIN” NUCLEATION (CCN BUDGET IN) b) WITH “BULK-MICROPHYSICS” NUCLEATION (INFINITE CCN RESERVOIRE)

26. GATE, Day 261: Concentration and mass of droplets “Bin” nucleation“Bulk” nucleation

27. “Bin” nucleation“Bulk” nucleation GATE, Day 261 : CCN concentration

28. THE ROLE OF AEROSOL BUDGET: Infinite reservoir of aerosols (“bulk” nucleation) leads to increase in rain

29. PRESTORM: Time evolution of rain water content Clear air (Maritime) Smoky air (Continental)