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UP: Fachverband Umweltphysik

UP 12: Atmosphäre - Labor

UP 12.3: Vortrag

Donnerstag, 20. März 2014, 10:15–10:30, MAG 100

Laboratory measurements on ice multiplication processes observed in individual cloud droplets — •Thomas Pander^{1 , 2}, Patricia Handmann², Alexei Kiselev², and Thomas Leisner^{1 , 2} — ¹Ruprecht-Karls-Universität Heidelberg — ²Karlsruher Institut für Technologie

Phase transitions in clouds have a profound influence on their radiative properties and lifetime. While it is common knowledge that water freezes at 0^∘C, cloud droplets can easily remain in a supercooled liquid state above -36^∘C. Heterogeneous freezing at warmer temperatures may be initiated by a suitable ice nucleus, ice itself being the ideal nucleus. As under typical conditions only a 10⁻⁵ fraction of the atmospheric aerosol particles are good ice nuclei, any multiplication processes of atmospheric ice particles are potentially relevant to the physics of the atmosphere. We present high-speed video evidence of such processes: a droplet may burst and emit several ice particles while freezing. The growing pressure in a liquid core surrounded by a growing ice shell can also be released by the pressing of water and dissolved gases through cracks in the shell, leading to bubbles on the outside of the droplet. If those bubbles burst, ice particles might be produced. The key influence of solid aerosol inclusions on these processes is explored and quantified.