New insights from continuous monitoring of ice nucleating particles in the Swiss Alps

Abstract:

The incomplete understanding of aerosol-cloud interactions introduces large uncertainties when simulating the cloud radiative forcing in climate models Aerosols support the phase transition of water in the atmosphere from a semi-stable to a thermodynamically preferred, stable phase. The physical and optical properties of a cloud, as well as the evolution of precipitation, are strong functions of the hydrometeors’ phase. Hence, the transition of droplets to ice crystals is of particular interest. One pathway to form ice crystals in the troposphere is via ice nucleating particles (INPs) which make up only a tiny fraction of all tropospheric aerosols. For accurate climate forecasts and projections, the parametrization of cloud processes and information such as the concentrations of INPs are needed. Presently, no continuous online INP counter is available and the data acquisition still requires a human operator.

To address this restriction, we developed “HINC-Auto”, a fully automated online INP counter, by adapting an existing custom-built instrument, the Horizontal Ice Nucleation Chamber (HINC) . HINC has successfully been used to detect INP concentrations during numerous field campaigns since 2014. HINC-Auto was deployed at the High Altitude Research Station Jungfraujoch (JFJ, 3580 m a.s.l., 46°33’ N, 7°59’ E) in February 2020 and by the time of submitting the abstract collected half a year of data.

The resulting continuous and more detailed temporal analysis of ambient INP concentrations allows observing repeated meteorological episodes compared to previous episodic events detected during a campaign. Our results indicate that the INP concentration in the free troposphere are elevated in spring compared to summer and winter. In addition, our results enable the comparison with lower time resolved parameters such as mass and concentration of PM10 species.