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.
Highlights
Understanding of cirrus cloud microphysics has advanced dramatically in the past several decades thanks to continual technical innovations in satellite remote sensing, in situ aircraft measurements, sophisticated laboratory experiments, and modeling that incorporates this new wealth of data
The au courant picture of cirrus clouds has emerged: a highly complex system that results in a vast array of cirrus formations, varying in time and location through interdependent mechanisms of microphysics, chemistry, dynamics, and radiation (e.g., Heymsfield et al, 2017)
It seems clear that both the sign and strength of cirrus radiative forcings and feedbacks depend on variables that can change with a wide array of parameters: geography; season; time of day; dynamical setting; and the concentrations, shapes, sizes, and textures of the cirrus ice particles themselves (e.g., Burkhardt and Kärcher, 2011; Harrington et al, 2009; Järvinen et al, 2018b, Yi et al, 2016)
Summary
Understanding of cirrus cloud microphysics has advanced dramatically in the past several decades thanks to continual technical innovations in satellite remote sensing, in situ aircraft measurements, sophisticated laboratory experiments, and modeling that incorporates this new wealth of data. It seems clear that both the sign (positive or negative) and strength of cirrus radiative forcings and feedbacks depend on variables that can change with a wide array of parameters: geography; season; time of day; dynamical setting; and the concentrations, shapes, sizes, and textures of the cirrus ice particles themselves (e.g., Burkhardt and Kärcher, 2011; Harrington et al, 2009; Järvinen et al, 2018b, Yi et al, 2016). Cloud-particle-imaging probes on research aircraft have contributed to major leaps in understanding, helping to constrain cirrus property satellite retrievals and climate modeling representations (Baumgarnder et al, 2017; Lawson et al, 2019) These probes deliver particle imaging and concentration measurements that yield unique insights into ice particle habits and distributions in cirrus, though several significant limitations remain. Beyond questions of particle morphology and radiative balances, major uncertainties around cirrus cloud evolution remain regarding particle nucleation pathways and the interconnected roles of aerosol chemistry, high-altitude humidity, and the subtle dynamics of vertical motion and turbulent eddies in cirrus
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