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UP: Fachverband Umweltphysik

UP 14: Atmosphäre - Spurengase, Aerosole und Labormessungen

UP 14.5: Talk

Thursday, February 28, 2013, 11:45–12:00, HS 5

How to compare contact and immersion freezing — •Nadine Hoffmann, Daniel Rzesanke, Denis Duft, Alexei Kiselev, and Thomas Leisner — Institute for Meteorology and Climate Research Atmospheric Aerosol Research (IMK-AAF), Karlsruhe Institute of Technology (KIT), Germany

The contact freezing of supercooled cloud droplets is one of the potentially important and the least investigated heterogeneous mechanism of ice formation in the tropospheric clouds [1]. Until now, the more ice active properties of contact freezing are still an unsolved mystery. In the experimental setup we are able to study single water droplets levitated in a laminar flow of aerosol particles. The particles are acting as contact or immersion freezing nuclei. The scavenging efficiency is calculated theoretically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. By repeating the freezing experiment for a sufficient number of times we were able to reproduce the statistical freezing behavior of large ensembles of supercooled droplets. The resulting freezing curves have a special shape depending on the rates of contact and immersion freezing. It will be discussed how to compare contact and immersion freezing. [1] - K.C. Young, The role of contact nucleation in ice phase initiation in clouds, Journal of the Atmospheric Sciences 31, 1974