Heidelberg 2015 – wissenschaftliches Programm

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UP: Fachverband Umweltphysik

UP 2: Atmosphäre

UP 2.22: Vortrag

Mittwoch, 25. März 2015, 16:30–16:45, G/gHS

Competition between contact and immersion freezing of supercooled water droplets induced by biological particles — •Nadine Hoffmann, Michael Koch, Denis Duft, Alexei Kiselev, and Thomas Leisner — IMK-AAF, Karlsruhe Institute of Technology

The contact freezing of supercooled cloud droplets is one of the potentially important and the least investigated heterogeneous mechanism of ice formation in tropospheric clouds [1]. To investigate this freezing mode we use an Electrodynamic Balance to levitate single water droplets in a laminar flow containing aerosol particles [2].

The particles can act as contact or immersion heterogeneous ice nuclei. 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 events. To demonstrate the relative importance of contact and immersion freezing modes on the shape of the resulting freezing curve, the results obtained with Birch Pollen Washing Water (BPWW) particles will be discussed in detail.

[1] - Ladino Moreno, L. A., Stetzer, O., and Lohmann, U.: Contact freezing: a review of experimental studies, Atmos. Chem. Phys., 13, 9745-9769, doi:10.5194/acp-13-9745-2013, 2013. [2] - Hoffmann, N., Kiselev, A., Rzesanke, D., Duft, D., and Leisner, T.: Experimental quantification of contact freezing in an electrodynamic balance, Atmos. Meas. Tech., 6, 2373-2382, doi:10.5194/amt-6-2373-2013, 2013.