1. Microstructure of Israeli Clouds and their Suitability for Seeding Eyal Freud and Daniel Rosenfeld יום עיון מחקרי רשות המים, 21 ביוני 2011.

2. 2  Mediterranean climate in northern and central Israel  50-70 days with precipitation annually  400-1200mm (comparable with Europe) but higher evaporation  Mostly convective precipitation  But significant orographic contribution  Mainly by a “Cyprus low”  Most prec. is post-frontal Introduction: Precipitation

3. 3 Background: Cloud Microphysics 0°C -40°C An example of the relation between r e and temperature in a hypothetical cloud. The different microphysical phases in the cloud are marked as well.

4. 4 Background: Cloud Seeding in Israel  Seeding with AgI for precipitation enhancement started in 1961  Aims at accelerating cold processes in the cloud and convert super-cooled cloud water into precipitation  Inexpensive water  Seeding effect is decreasing with time (15%  0%)  “Hot” scientific debate  “Israel 4” experiment

5. 5 Main Objective Characterize the microphysical properties of the clouds in northern Israel and assess their suitability for seeding

6. 6 Approaches  Aerosol measurements below cloud base over sea and inland  Cloud vertical profiling from base to top (discrete levels or spiral) to document:  Droplet growth  Precipitation formation  Total (supercooled) LWC  Satellite analysis

7. 7  Ambient:  Temperature; Pressure (static, dynamic); GPS  Aerosols:  CN  CCN  PCASP-X2  Clouds/Precipitation:  CAS  CIP  CDP  Hot Wire LWC  Acquisition software: PACS, PADS (DMT), Hyper Terminal Instrumentation

8. 8 Execution: 2008-2011  22 Sorties in the last three seasons in various conditions (thermodynamic and aerosol)  Total ~60hrs  Plenty of data  A few challenges  Constant improvement

9. 9 A rainy day in Northern Israel Galilee Golan

10. 10 Results Is there any seeding potential in the Israeli clouds?  ~10,000 data points  No separation between seeded/unseeded, and different cloud types  Abundant super- cooled LWC at around -10ºC

11. 11 Results  20100228: Windy  Close to the sea  Pollution  20100412: Haze / Dust  No gradient except in pollution (R&B)  20100326: Calm and Clear  No giant CCN even near shore (G) Giant CCN – Where and when?

12. 12 Results  Tail over Sea 20100228  Tail over sea 20091213 (CAS)  No tail mid level cloud 20100120  Tail over Galilee 2010228  Tail over Galilee (dust) 20100412  Small Tail over Golan 20100318  No tail over shore 20100326 Giant CCN effect on DSD?

13. 13 Results  How do we define the onset of precipitation?  A decent proxy is the cloud droplet effective radius. Around 11μm probability increases the most.  Clouds had to acquire a minimum depth of 1 to 3km for the cases with higher droplet Concentration When did clouds precipitate?

14. 14 Summary and Conclusions (1)  Coastal range orographic clouds are often naturally seeded by ice hydrometeors falling from mature convective clouds  On windy days sea spray seeds the clouds hygroscopically, with greatest effect near the coast  Desert dust can also act as a natural seeder Quite effective natural seeding but…

15. 15 Summary and Conclusions (2)  There are still decent amounts of super-cooled cloud liquid water in certain clouds = Potential for seeding  Seeding efforts should be shifted to the eastern range and focused on orographic clouds where less natural seeding occur  Real time satellite imagery should be used to identify the target clouds with super-cooled LWC.  Pursuing radar echoes, i.e. already precipitating clouds, is redundant

16. 16 Thanks for your attention! Questions???