Study of Freezing Behavior of Supercooled Cloud Droplets in Electrodynamic Levitator
Abstract
An Electrodynamic Balance (EDB) of a quadrupole type, also known as a Paul trap, is a powerful tool to study atmospherically relevant processes in individual cloud droplets. Paul trap allows for contact-free observation of the phase transition processes, uptake of the aerosol, trace gases, and water vapor by liquid water droplet and ice crystal, elastic and inelastic light scattering, homogeneous and heterogeneous freezing of undercooled droplets of water solutions, growth and sublimation of ice crystals, and various charge induced effects like evaporation stabilization or Coulomb instability of electrified microdroplets. Recently, the Paul trap research group at IMK-AAF (KIT) has achieved several important improvements concerning accuracy of the temperature and humidity control inside the EDB, thus turning it into a practical laboratory-scale single-particle cloud chamber that is comparable with the more commonly used expansion chambers or continuous flow diffusion chambers (CFDC). Combination of EDB with an aerosol generation system allows for investigating the droplet / ice / aerosol interaction mechanisms, like electroscavenging of aerosol particles or freezing of supercooled droplet colliding with an aerosol particle (contact freezing). The latest experiments with supercooled water droplet suspended in the laminar flow of monodisperse mineral dust particles (kaolinite, illite) have shown a clear dependence of contact freezing probability on the nature and size of aerosol particle. Of particular interest are the observations of ice growth on the surface of a levitated frozen droplet at controlled temperature and humidity, since they confirm the known relationship between the preferential shape of growing ice crystals and temperature and humidity of the surrounding air. Observations of droplet freezing with the help of ultrafast microscope ( up to 200.000 frames/s) allowed us to measure the rate of ice/water interface propagation inside the freezing droplet and establish the temporal evolution and temperature dependence of ice growth path. Utilization of ultrafast microscopy has made it also possible to study the probability of droplet fragmentation upon freezing. It was shown, that the frequency of fragmentation events is a function of temperature and concentration of insoluble particles inside the droplet. This data might prove being useful for understanding the mechanisms of secondary ice formation in tropospheric clouds.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A21E..07K
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0320 ATMOSPHERIC COMPOSITION AND STRUCTURE / Cloud physics and chemistry;
- 0365 ATMOSPHERIC COMPOSITION AND STRUCTURE / Troposphere: composition and chemistry;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques