AE31B-0442
Ionization, Charging and Electric Field Effects on Cloud Particles in the CLOUD Experiment

Wednesday, 16 December 2015
Poster Hall (Moscone South)
Leonid Nichman1, Emma Järvinen2, Robert Wagner3, James Dorsey4, António Miguel Dias5, Sebastian Ehrhart5, Jasper Kirkby6, Martin William Gallagher4, Clive P Saunders1 and CLOUD Collaboration, (1)University of Manchester, Manchester, M13, United Kingdom, (2)Karlsruhe Institute of Technology, Karlsruhe, Germany, (3)University of Helsinki, Division of Atmospheric Sciences, Department of Physics, Helsinki, Finland, (4)University of Manchester, Manchester, United Kingdom, (5)CERN European Organization for Nuclear Research, Geneva, Switzerland, (6)CERN European Organization for Nuclear Research, Physics, Geneva, Switzerland
Abstract:
Ice crystals and frozen droplets play an important role in atmospheric charging and electrification processes, particularly by collision and aggregation. The dynamics of charged particles in the atmosphere can be modulated by Galactic Cosmic Rays (GCR). High electric fields also affect the alignment of charged particles, allowing more time for interactions.

The CLOUD (Cosmics Leaving OUtdoor Droplets) experiment at CERN has the ability to conduct ionization, charging and high electric field experiments on liquid or ice clouds created in the chamber by adiabatic pressure reductions. A pion secondary beam from the CERN Proton Synchrotron is used to ionize the molecules in the chamber, and Ar+ Corona Ion Generator for Atmospheric Research (CIGAR) is used to inject unipolar charged ions directly into the chamber. A pressurized airgun provides rapid pressure shocks inside the chamber and induces charged ice nucleation. The cloud chamber is accompanied by a variety of analysing instruments e.g. a 3View Cloud Particle Imager (3V-CPI) coupled with an induction ring, a Scattering Intensity Measurements for the Optical detection of icE (SIMONE) and a Nano-aerosol and Air Ion Spectrometer (NAIS). Using adiabatic expansion and high electric fields we can replicate the ideal conditions for adhesion, sintering and interlocking between ice crystals.

Charged cloud particles produced measurable variations in the total induced current pulse on the induction ring. The most influential factors comprised initial temperature, lapse rate and charging mechanism. The ions produced in the chamber may deposit onto larger particles and form dipoles during ice nucleation and growth. The small ion concentration was monitored by the NAIS during these runs. Possible short-term aggregates or alignment of particles were observed in-situ with the SIMONE. These and future chamber measurements of charging and aggregation could shed more light on the ambient conditions and dynamics for electrification in the atmosphere.

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