1. COPE PRESENTATION Process Modeling and Ice Nuclei

2. Current Status Show results from convective clouds near Chilbolton These are shallow clouds with tops around -7C Show rapid glaciation small amounts of primary ice deduced from measurements of aerosol followed by rapid glaciation Key issues Origin of first ice when does it form ? What are the ice nuclei, CCN number of droplets. Role of Organic and dust aerosol in this input from ACIDPRUF (lab studies of ice nucleation) Role of secondary ice (mainly Hallett-Mossop) but is splintering of supercooled raindrops important outside the H-M zone ? How does secondary ice contribute to the precipitation production in the cloud

3. B425 (22/01/09) - Run 1 (13:17-13:42z) Alt 1.3km (-1.0 ± 0.1ºC) (eastbound)

4. B425 (22/01/09) – Run 3 (13:56-14:15z) Alt 1.26km (-3.5 ± 0.3ºC) (eastbound)

5. B425 (22/01/09) – Microphysics summary Key: red dot =1Hz data point, diamond = median, circle = mean, blue dots = +/- one sd from mean

6. B425 (22/01/09) – Aerosol size measurements – Ground and Aircraft (PCASP)

7. Aerosol Cloud and Precipitation Interactions Model (ACPIM) (Connolly et al., 2009) run as a Microphysics Cloud Parcel model 1.Treats the hygroscopic growth and cloud activation of mixed aerosol including organic material (following Topping et al., 2005) 2.The activation of the ice phase using an IN parameterisation (eg DeMott et al., 2010) or results from laboratory experiments 3.The growth of ice particles by vapour diffusion, riming and aggregation 4.Precipitation 5.Secondary ice splinter production by Hallett- Mossop SIP process. Aerosol input to ACPIM includes: Observed size distribution and composition (here from AMS, WIBS, and filter analyses) sensitivity tests to: composition distribution (internal/external mixtures); updraught predicted CCN number (c.f. measured values below CB at 0.08 0.12% SS) cloud droplet number then other sensitivity tests examining primary IN and HM (SIP)

8. Sensitivity to increasing IN number (here by shifting T input in DeMott (2010) parameterisation) B425 (22/01/09) – ACPIM sensitivity tests to increasing IN number HM (switched on) Maximum Ice Crystal Concentration (L -1 ) Time (min) to reach 100 L -1 concentration HM (switched off) HM (high aerosol input)

9. B425 (22/01/09) – ACPIM simulations: Summary 2 1.HM powerful process – generating 3 orders magnitude more ice than IN parameterisations predict (e.g De Mott 2010) 2.Key to this: aerosol input (CCN number) – need large droplets to be present (formed by collision-coalescence) 3.IN number: Need sufficient primary ice particles to produce rimer particles and initiate HM (but if too many IN present then primary ice removes drops by Bergeron-Findeisen -turning HM process off) But what is the source of primary IN?

10. Model used extrapolate results up to higher temperatures B425 (22/01/09) – IN from ice nuclei Surface area dependent Active Sites concept obs spectrum & SAS at -7ºC give ~10 -2 L -1 IN

13. Developments needed Detailed measurement of aerosol input to cloud (size and composition) and on board aircraft. Measurements of first ice in the cloud (3V-CPI) for size distribution, CAS for polarisation, SID ? for very small ice particles Model needs improved treatment of ice nucleation by organic aerosol in particular, can we discriminate between dusts. Model needs to incorporate drop freezing as a source of splinters ? Use data and models to identify relative roles of primary nucleation and secondary ice in cloud development (dynamics and precipitation)