Quantitative Laboratory Experiments on Contact Freezing and Secondary Ice Production induced by Aerosol- Cloud Droplet Collisions

Tuesday, 16 December 2014: 4:20 PM
Thomas Leisner1, Alexei A Kiselev2, Nadine Hoffmann1, Thomas Pander1 and Patricia Handmann1, (1)Karlsruhe Institute of Technology, Karlsruhe, Germany, (2)Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany
We report on laboratory experiments on contact freezing probabilities and secondary ice processes accompanying the contact- or immersion freezing of cloud droplets. The freezing of individual, electrodynamically levitated cloud droplets was initiated by contacting them with ice nuclei or by immersed ice nuclei. The freezing process itself and secondary ice formation by either splintering of the freezing droplet or the ejection of gas bubble membranes has been observed and analyzed by high speed light microscopy. In our contribution, we classify these processes and quantify their temperature dependent probability as a function of the mode of freezing and the presence of immersed particles. Contact freezing probabilities have been calculated from the measured freezing rates and contact rates, the latter being determined offline by counting the number of scavenged particles under and environmental scanning electron microscope.