Characterization of small cloud ice particles in mixed phase clouds

Clouds alter the Earth's radiative properties and are a major component of the hydrological cycle. Common clouds in mid-latitudes are mixed phase clouds, which contain both ice particles and water droplets. The ice phase is of great importance to both the lifetime and the radiative properties of mixed phase clouds. During the CLACE2013 and CLACE2014 field campaigns at the High Alpine Research Station Jungfraujoch 3580m.a.s.l.we investigated the microphysical ice particle properties of such clouds. Due to the very dynamic evolution of ice particles in the presence of liquid droplets we restrict ourselves to the analysis of small ice particles. In order to characterize these small cloud ice particles we deployed the Small Ice Detector (SID3) to sample the cloud directly and the Particle Phase Discriminator (PPD2-K) as part of the Ice Selective Inlet (ISI, contribution by Kupiszewski et al. to this conference). Simultaneously to the measurements of the SID3 and PPD2-K residuals of small ice particles were counted and characterized downstream of the Ice Counterflow Virtual Impactor (ICE-CVI, Mertes 2007) and the ISI.

The SID3 and the PPD2-K generate equivalent measurements which are a number size distribution and high resolution two dimensional scattering patterns of individual cloud particles from which the particles size, phase and morphology can be inferred (Kaye 2008). While the Jungfraujoch station was in a mixed phase cloud, the SID3 sampled both liquid water droplets and ice particles. Typically, the liquid water droplets outnumbered the small ice particles by some orders of magnitude, thus most of the high resolution scattering patterns acquired by the SID3 show water droplets. The ICE-CVI and the ISI, however, transmit ice particles only. As part of the ISI, the PPD2-K sampled no water droplets but exclusively small cloud ice particles. The selective sampling allows for a highly detailed analysis of the small ice particles with respect to number and morphology.

Furthermore, the measurements of ice residual number concentration downstream of the ICE-CVI and the ISI are compared to the measurements of both the PPD2-K and the SID3.