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 2016–2019, 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 mesoscale 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

“…Based on analyses of vapor growth rates encompassing a wide range of droplet properties as well as nucleation and environmental conditions, laboratory measurements show that α ranges from about 0.001 to unity (Harrington et al., 2019). In line with recent balloon‐borne measurements that show details of cirrus ice crystal surfaces (Magee et al., 2021), we model depositional growth of newly nucleated ice crystals with step nucleation.…”

“…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.…”

“…Together, these equations mean that α k is determined by diffusion of H 2 O molecules through the air and by surface kinetic processes. We solve Equations + iteratively for α k , that is, separately for each ice crystal class, with $$${s}_{\text{crit}}\,[\%]=3.7955+0.10614x+0.0075309{x}^{2},\quad x=T\,[\mathrm{K}]-273.15$$$ and μ = 10 (Harrington et al., 2019), supported by in situ data (Magee et al., 2021).…”

“…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.…”

A Light-Weight Holographic Imager for Cloud Microphysical Studies from an Untethered Balloon

“…Untethered sounding balloons can be deployed in most atmospheric conditions, allowing in situ measurements throughout the full vertical extent of clouds. Various instruments have been deployed on sounding balloons for the study of clouds, including impaction sensors (Magee et al, 2020), cloud condensation nuclei counters (Delene and Deshler, 2001), 2D video microscopes (Takahashi et al, 2019), and standard radiosondes that measure pressure, temperature, and humidity.…”