1. Ice-Ice Collisions: An Ice Multiplication Process in Atmospheric Clouds by Vaughan Phillips (Uni. of Hawaii) Jun-Ichi Yano(Meteo France)

3. Main Message: ice-ice collision can lead to “explosive” ice multiplication zero-dimensional model >1 single parameter:

4. background: ice nuclei (IN) is Rare: Mixed Phase However: IN # << ice particle # ice multiplication?

5. ice multiplication (observational evidence): (Hobbs 1969) Ice particle# IN # Ice particle#

6. background: ice nuclei (IN) is Rare: Mixed Phase However: IN # << ice particle # ice multiplication? Main Message: ice-ice collision can lead to “explosive” ice multiplication along with Hallet- Mossop process

7. Ice-ice collison breakup : Experiment by Takahashi et al., (1995):

8. Ice-ice collision-breakup multiplication (nonlinear): r0r0 vTtvTt

9. Zero-Dimensinoal Model: primary ice generation rate = constant igG c0c0  f = 10min  g = 30min  i = 15min ice+ice collision ~  ice crystal (i), small graupel (g), large graupel (G) ~

10. lag model : numerical analysis relaxation model : analytical study

11. relaxation model analysis :

12. lag model analysis : c-dependence: Ice Enhancement Ratio: IE = n i /n i *

13. lag model analysis :  g -dependence: Ice Enhancement Ratio: IE = n i /n i *

14. lag model analysis : with Supercooled Rain Aloft: Ice Enhancement Ratio: IE = n i /n i *

15. lag model analysis : Hallet-Mossop process: Ice Enhancement Ratio: IE = n i /n i *

16. saturation -1% supersaturation lag model analysis : water-vapor depletetion (Korolev and Mazin 2007): Ice Enhancement Ratio: IE = n i /n i *

17. Conclusion The Ice-Ice Collision Ice-Breakup leads to “Nonlinear” Explosive Ice- Multiplication Porcess. Potentially more powerful than Hallete- Mossop process >1 single parameter:

18. ice multiplication processes: Hallet-Mossop (1974): (-3C)-(-8C): well established (Phillips et al., 2001, 2003, 2005, 2007, 2009) Ice-ice collison breakup (Hobbs&Farber 1972, Vardiman 1978, Takahashi et al., 1995): graupel + (large) graupel (small) graupel + (large) graupel + (small) graupel + supercooled cloud droplets (>24  m) rimed + graupel splinter ice splinter Ice (Ice Crystals) not well studied: established by this Talk

20. relaxation model analysis :

24. lag model analysis (numerical): example nini ngng nGnG n i *: without ice multiplication ii gg ff Ice Enhancement Ratio: IE = n i /n i *

25. ?

26. summary a high IE ratio of 10 4 is attained about an hour af in standard run without supercooled rain the time for an IE ratio to exceed 10 4 is shortened to only 20 min with supercooled raindrops the HM process starts much sooner than mechanical break-up if active inclusion of the response of humidity to explosive ice multiplication yields a maximum IE ratio of the order of about 10 5