CCN and INP Abilities of Hybrid Flare Particles Measured with MRI Continuous-Flow Diffusion Chamber-Type IN Counter and MRI Cloud Simulation Chamber

As a part of “advanced study on precipitation enhancement in arid and semi-arid regions” is supported by The United Arab Emirates Research Program for Rain Enhancement Science (UAEREP), physico‐chemical properties, such as size distribution, cloud condensation nuclei (CCN) and ice nucleating particle (INP) abilities of "hybrid flare" have been investigated by using CCN counter, IN counter and several aerosol instruments in order to clarify the effectiveness of this seeding method. The hybrid flare is a mixture of two different types of flares; hygroscopic flare and silver iodide (AgI) flare. We had tested airborne hygroscopic flare as one of the hygroscopic seeding technique, and also tested AgI flare as one of the glaciogenic seeding technique in the past years. We are focusing on hygroscopic parameter κ and temperature‐deterministic ice nucleation active surface site (INAS) density for each particle size mode like other agents investigated before.

The dry particle size distributions of hybrid flare agents typically had a mode at around 140‐170 nm, being about the same size as that of hygroscopic flare particles. The κ‐value mostly exceeded 0.3, which were comparable to that of typical atmospheric aerosols, and also higher than representative κ‐value of pure mineral dust particles that can be assumed as background aerosol in arid and semi‐arid regions. The large portion of submicron particles was predominantly affected by both potassium chloride and calcium chloride included in individual particles. Those materials have strong hygroscopicities. Additionally, most of hybrid flare particles were also mixed with tiny AgI particles. The number of INP induced per gram of hybrid flare agents measured by IN counter and the derived INAS density at water supersaturation of five percent at temperatures of ‐10, ‐15, ‐20 and ‐25 °C were about 10¹¹‐10¹³ particles/gram and 10¹⁰‐10¹² m^‐2, respectively. The results also indicated that hybrid flare particles will act as not only immersion freezing nuclei, but also deposition nuclei. The hybrid flare particles eventually act as more effective ice nucleating particles than the atmospheric aerosols in clouds as well as AgI flare particles do. Size dependency of hybrid flare particles’ INP ability has been also studied using size selected particles from hybrid flare. Further investigations of the effects of hybrid flare particles on initial microphysical structures of clouds will be performed using the MRI cloud simulation chamber.