CAWSES Project - Detection of electrically ...
Detection of electrically charged clouds and aerosols by means of second harmonic generation (SHG) at the droplet-air interface.
Dr. Kamil Stelmaszczyk
Institut für Meteorologie
Despite the recognized correlation between variations of Galactic Cosmic Rays (GCRs) flux and cloudiness the precise mechanism of coupling between GCR induced ionization and cloud formation processes is still not fully known, however, there is a general agreement that charged particulates and aerosols play an important role in cloud microphysics. Recently physical phenomena like Coulomb explosions and formation of Rayleigh jets have been recognized as possible source of ultra fine, highly charged particles in clouds. For this reason we propose to perform novel and unconventional measurements of spatial and temporal profiles of charged particulates in the atmosphere, which will be helpful not only in finding the correlations between electrified particulates and aerosol/cloud occurrences, but also in validating existing models of clouds formation. Our measurements will consist in sending the ultra-short, femtosecond laser pulse into the atmosphere and detecting the following SHG signal. Second Harmonic Generation (SHG) at liquid/gas interfaces can be used as an indicator of the interface electrical charges, which are responsible for inducing a surface polarization and thus introducing X³ processes. For this reason the SHG signal from clouds or aerosols can be expected as an indicator of charged droplets. Preliminary laboratory studies of SHG at surfaces of charged droplets will also be performed. They will aim at characterizing the SHG process in the context of its suitability for outdoor applications. In particular, measurements of the SHG efficiency and its angular dependence will be performed.