Captured cirrus ice particles in high definition

Abstract

Abstract. Cirrus clouds composed of small ice crystals are often the first solid matter encountered by sunlight as it streams into Earth's atmosphere. A broad array of recent research has emphasized that photon particle scattering calculations are very sensitive to ice particle morphology, complexity, and surface roughness. Uncertain variations in these parameters have major implications for successfully parameterizing the radiative ramifications of cirrus clouds in climate models. To date, characterization of the microscale details of cirrus particle morphology has been limited by the particles' inaccessibility and technical difficulty in capturing imagery with sufficient resolution. Results from a new experimental system achieve much higher-resolution images of cirrus ice particles than existing airborne-particle imaging systems. The novel system (Ice Cryo-Encapsulation by Balloon, ICE-Ball) employs a balloon-borne payload with environmental sensors and hermetically sealed cryo-encapsulation cells. The payload captures ice particles from cirrus clouds, seals them, and returns them via parachute for vapor-locked transfer onto a cryo-scanning electron microscopy stage (cryo-SEM). From 2015–2019, the ICE-Ball system has successfully yielded high-resolution particle images on nine cirrus-penetrating flights. On several flights, including one highlighted here in detail, thousands of cirrus particles were retrieved and imaged, revealing unanticipated particle morphologies, extensive habit heterogeneity, multiple scales of mesoscopic roughening, a wide array of embedded aerosol particles, and even greater complexity than expected.

Studies on the Competition Between Homogeneous and Heterogeneous Ice Nucleation in Cirrus Formation

“…We simulate H 2 O mass uptake during the rather short ice formation stage by assuming a simplified ice growth model and approximating the shape of real ice crystals by volume‐equivalent spheres (Section 2.4). To date, it is not possible to fundamentally resolve the issue of ice growth in view of the complexity of cirrus ice particle morphology, complexity, and mesoscopic surface roughness on the one hand (Magee et al., 2021) and due to the absence of a consensus on how real‐world ice crystal habits can be predicted on the other. However, we drop the common assumption of constant ice growth efficiency and use deposition coefficients on ice that depend on ice supersaturation and other variables.…”

“…Recent balloon‐borne in situ sampling of cirrus ice crystals, combined with cold‐stage electron microscopy, reveals that polycrystalline ice crystals (polycrystals) dominate the habit of cirrus ice crystals (Magee et al., 2021). Even at small sizes, these crystals are sharply faceted and often with hollowed regions.…”

Effect of Polygonal Agglomerated Ice Crystals on Laser Scattering

“…According to the statistical data and figures provided by Magee et al [10], the main shape of the ice crystal particles with a size of 1-100 µm is shown in Figure 1. In addition to the immeasurable complex poly-crystals and damaged bullet bodies, among the single particles with modeling significance, the approximate hexagonal prism accounts for the largest number, and its cross-sectional area accounts for the largest proportion of the total area (about 60%).…”

“…However, with the improvement of the cirrus cloud ice crystal particle capture technology, a clearer understanding of the microscale details of cirrus particles has been attained. In 2021, Magee et al [10] developed a cryoencapsulated balloon system to capture ice particles and observe the microscopic morphology of particles via cryoscanning electron microscopy. They found that cirrus clouds are formed from random clumps of amorphous ice crystals of various shapes.…”

“…Based on the latest observations of Xiao et al [1] and Magee et al [10], in this study, the ice crystal particle shapes accounting for the largest proportion of particles were taken as the research object. Considering the inhomogeneity and randomness of ice crystal distribution, four ice crystal agglomeration models are established, including spheresphere, sphere-ellipsoid, sphere-hexagonal plate, and sphere-hexagonal prism models.…”