Erlangen 2018 – wissenschaftliches Programm
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UP: Fachverband Umweltphysik
UP 9: Poster session
UP 9.8: Poster
Mittwoch, 7. März 2018, 16:15–18:15, Orangerie
The formation of ice in noctilucent clouds — Mario Nachbar1, Denis Duft2, and •Thomas Leisner1,2 — 1University of Heidelberg, Heidelberg, Germany — 2Karlsruhe Institute of Technology, Karlsruhe, Germany
Noctilucent clouds are the highest occurring clouds in the terrestrial atmosphere. They form heterogeneously on sub-2nm meteor smoke particles at about 86km height in the polar summer mesopause, the coldest and also one of the dryest regions of the atmosphere. It is for these extreme conditions and the difficulty of in-situ measurements that the formation process of noctilucent clouds is still not well understood. In this contribution we present laboratory measurements on the ice formation at mesopause conditions on small metal oxide nanoparticles as a substitute for meteor smoke particles. We show that, in contrast to the current assumption of crystalline ice nucleation, amorphous solid water forms on the nanoparticle surface and that ice growth is activated above the equilibrium saturation for amorphous ice. The experimental method is based on the analysis of ice particle growth rates which also allows to measure the saturation vapor pressure over the amorphous ice phase between 130K and 160K. We show that the saturation vapor pressure was underestimated by more than a factor of two in the past.