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UP: Fachverband Umweltphysik

UP 7: Atmosphere - lab studies

UP 7.1: Hauptvortrag

Dienstag, 6. März 2018, 17:30–18:00, G 1.011

Ice formation and crystallization in mesospheric clouds — •Denis Duft¹, Mario Nachbar², and Thomas Leisner^1,2 — ¹Karlsruhe Insitute of Technology, Karlsruhe, Germany — ²University of Heidelberg, Heidelberg, Germany

In this contribution we present results from a laboratory experiment designed to study the formation of ice at cold conditions. Specifically, we investigate the heterogeneous formation of ice on small aerosol particles which provide the surface for ice formation in the mesosphere. We show, that amorphous solid water, a highly viscous non-crystalline ice phase similar to supercooled liquid water, is the water ice phase which deposits from the gas phase below 160K, even though it is thermodynamically unstable and crystallizes above 120K. We also show, that amorphous solid water crystallizes to small nano-crystallites which greatly influence the properties of the ice phase. The nano-crystals are stable for hours below 160K and for even longer times at lower temperatures such that nano-crystalline ice can be regarded as a separate ice phase on atmospheric time scales. Only at temperatures above 160K the nano-crystalline ice transforms to micro-crystalline ice whose properties are typically given in textbooks.