Cloud chamber laboratory investigations into scattering properties of hollow ice particles

Abstract

Copyright 2015 The Authors. Published by Elsevier Ltd.This is an open access article under the CC-BY license (http://creativecommons.org/licenses/by/4.0/). Date of Acceptance: 16/02/2015Measurements are presented of the phase function, P11, and asymmetry parameter, g, of five ice clouds created in a laboratory cloud chamber. At ???7 ??C, two clouds were created: one comprised entirely of solid columns, and one comprised entirely of hollow columns. Similarly at ???15 ??C, two clouds were created: one consisting of solid plates and one consisting of hollow plates. At ???30 ??C, only hollow particles could be created within the constraints of the experiment. The resulting cloud at ???30 ??C contained short hollow columns and thick hollow plates. During the course of each experiment, the cloud properties were monitored using a Cloud Particle Imager (CPI). In addition to this, ice crystal replicas were created using formvar resin. By examining the replicas under an optical microscope, two different internal structures were identified. The internal and external facets were measured and used to create geometric particle models with realistic internal structures. Theoretical results were calculated using both Ray Tracing (RT) and Ray Tracing with Diffraction on Facets (RTDF). Experimental and theoretical results are compared to assess the impact of internal structure on P11 and g and the applicability of RT and RTDF for hollow columns

Air pockets and secondary habits in ice from lateral-type growth

“…But at low supersaturations, the hollow often varies in width, getting wider, then getting narrower, and finally closing-off into a center pocket. Oscillations also occur at middling-to-high supersaturations (e.g., Smith et al, 2015), but are much more pronounced at the low supersaturations in our experiments here. Gonda and Koike (1983) also observed the closing-off of hollows during growth at one atmosphere and supersaturations up to 33% at −30 °C.…”

“…But ice and snow crystals usually have more complex shape features, such as hollows and branches, known as the secondary habit (e.g., Kikuchi et al, 2013). These features have recently attracted attention because the crystal "complexity" affects radiative scattering of ice-containing clouds (e.g., Smith et al, 2015;Järvinen et al, 2018). 25…”

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.…”

Halo ratio from ground-based all-sky imaging

“…11a and 13a). The shift of the halo peak towards larger angles than the 22 • shown by the more familiar single-scattering SPF computed from geometric optics can be interpreted as originating from the combined contributions from background sky scattering, diffraction effects (due to small crystal size) and crystal roughness (Macke et al, 1996;Ulanowski, 2005;Liu et al, 2013;Smith et al, 2015). The SPF was obtained by taking the mean of the three camera channels.…”