Laboratory experiments on 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 be the major kind of nuclei for the formation of so called NoctiLucent
Clouds (NLCs) in the polar summer mesosphere. However, describing the formation process of these clouds
is flawed with large uncertainties mainly due to a lack of experimental data on their microphysical formation
process.
To investigate these processes, we produce single charged nanometer sized (1-3 nm) MSP analogues in a
microwave plasma particle source. The particles are suspended in a carrier gas and transferred to a vacuum setup
where they are stored in a linear ion trap (MICE). The trap allows us to apply realistic mesopause conditions
in terms of temperature, background pressure and water vapor concentration. By using a time-of-flight mass
spectrometer, we are able to observe adsorption and, if nucleation occurs, subsequent deposition of water vapor on
the MSP analogues as a function of saturation and residence time in MICE. From these experiments, we determine
critical saturations needed to activate cloud formation. ... mehrHowever, NLCs occur during polar summer and therefore
are exposed to sunlight. At the low pressures of the mesopause, MSPs may heat up with respect to the background
gas temperature which significantly influences the critical saturation needed to activate cloud formation. We
expose the MSP analogues trapped in MICE to laser light of a known radiation profile in order to determine the
heat up of the particles as well as the resulting influence on the nucleation process. The results of our experiments
describe the microphysical H 2 O nucleation process on MSPs at realistic mesopause conditions and therefore can be
used in models to describe the formation of NLCs and countercheck the results with observational cloud properties.