Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds

Abstract

Abstract. This study reports on the origin of small-scale ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super-and subsaturated ice conditions and for temperatures in the −40 to −60 • C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Small-scale ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high crystal complexity dominates the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapor during the crystal growth. Indications were found that the small-scale crystal complexity is influenced by unfrozen H 2 SO 4 /H 2 O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers: the polar nephelometer (PN) probe of Laboratoire de Métérologie et Physique (LaMP) and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side and backward scattering directions. It was found that these functions have a rather low sensitivity to the small-scale crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.

PHIPS-HALO: the airborne particle habit imaging and polar scattering probe – Part 2: Characterization and first results

“…Laboratory and modeling studies have shown that the angular light scattering properties of randomly oriented complex ice particles strongly differ from those of pristine crystals (Ulanowski et al, 2006;Smith et al, 2015;Schnaiter et al, 2016;Baum et al, 2010;Baran, 2012). While pristine hexagonal ice crystals show the 22 and 46 • halo features as well as the ice bow feature at scattering angles between about 135 and 160 • , the angular light scattering of complex crystals is characterized by a flat and featureless function with larger scattering cross sections for side and backscattering directions.…”

“…However, the predecessor PHIPS-HALO nephelometer with the old fiber coupler was compared with the PN for ice particle ensembles generated in cirrus simulation experiments in the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber (Fig. 7 of Schnaiter et al, 2016). For this comparison the averaged angular scattering functions from PHIPS-HALO were corrected for channel crosstalk and channel sensitivity characteristics as described in Part 1.…”

Vertical distribution of the particle phase in tropical deep convective clouds as derived from cloud-side reflected solar radiation measurements

“…The bulk aspherical fraction is derived from the number of aspherical particles to the number of total particles measured between 3 and 50 µm s −1 . Calibration of the backward channel was performed during RICE03 (Rough ICE campaign) at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber Schnaiter et al, 2016). Spherical liquid particles reveal a low AF (< 0.1) while aspherical particles (ice or aerosols) have a high AF (> 0.1, mean of 0.4).…”

The WeIzmann Supercooled Droplets Observation on a Microarray (WISDOM) and application for ambient dust

“…Therefore, they can influence present and possibly future climate IPCC, 2013). Studying ice formation in clouds is hence important, and yet, due to its complexity, this process is still not fully understood and presents a great challenge to laboratory and field researchers as well as for clouds and climate modelers (DeMott et al, 2010;Schnaiter et al, 2016;Ullrich et al, 2017).…”