Properties of pure ice and mixed-phase clouds in an alpine environment during CLACE2013 at Jungfraujoch, Switzerland

During January and February 2013, the CLACE2013 experiment took place at the High Alpine Research Station Jungfraujoch, Switzerland. This experiment was designed to investigate the properties of aerosol particles and hydrometeors in order to understand heterogeneous nucleation and freezing processes in clouds. In this work, we compare measurements of several instruments measuring liquid and ice cloud particles during two measurement periods in different meteorological conditions.

In the first case, a thin ice cloud (often called diamond dust) formed during the late evening hours (between approx. 20:30 and 23:00 UTC) os 08 Feb 2013 in an ice-supersaturated but water-subsaturated environment around -29°C. The ice particles in the cloud were 50 - 100 µm in equivalent diameter and at low number concentrations (1 - 10 particles per liter on average). The second case is a precipitating Nimbostratus cloud during the passage of a cold front on the evening of 27 Jan 2013. In this case, supercooled liquid droplets, and small and large ice crystals were present in vertical velocities of order 5 to 10 m/s from the northern side of the Jungfraujoch. Therefore, both ice particles and supercooled droplets could coexist over a fairly long time period without the ice particles drying out the water droplets. Here we are particularly interested in the ice / liquid water partitioning and the condensation and evaporation processes of cloud droplets in the vicinity of large ice particles. Shown are a comparison of instrument measurements of the cloud particles of the pure ice cloud and mixed-phase cloud in these two cases.