The microphysical formation process of Noctilucent Clouds

Ablated meteoric material condensates in the upper atmosphere to nanometer sized meteoric smoke particles (MSPs). These particles are believed to serve as nuclei for the formation of so called NoctiLucent Clouds (NLCs) which appear in the polar summer mesopause. However, describing the formation process of these clouds comes hand in hand with large uncertainties mainly due to a lack of experimental data on their microphysical formation process. We produce single charged nanometer sized (1-3 nm) MSP analogues and expose them to realistic mesopause conditions in terms of background pressure, temperature, radiation and water vapor concentration. A time of flight mass spectrometer allows us to observe adsorption and deposition of water vapor subsequent to nucleation as a function of temperature and saturation. This contribution will introduce the nucleation formalisms used to describe the formation of NLCs and will compare these to the latest experimental results of water vapor nucleation on different MSP analogues. Measurements of the adsorption process of water vapor on the pure MSP particles as well as critical saturations as function of particle size and background temperature will be presented. ... mehrIn addition, the heat up of MSPs by absorption of background radiation and its influence on the nucleation process will be highlighted.