Balloon-Borne Measurements of Midlatitude Cirrus Ice Crystals: Morphology and Cirrus Simulations

Description

Seven separate cirrus cloud systems were sampled with a balloon-borne device that passively captures in-situ ice crystals during the Ice Cryo-Encapsulation Balloon (ICE-Ball) experiment that occurred in October 2021 over the ARM SGP site. Crystals are captured in a dry-ice cooled cell that is magnetically sealed once collection is compete. The sealed cell is stored in liquid nitrogen once the system returns to the surface, allowing for later interrogation of the crystals with a cryo-stage scanning electron microscope (cryo-SEM). Sampled crystals show a rich diversity of complex crystalline habits. Some of the cirrus cases were dominated by rosette crystals, though the branching arms were made of scrolls and sheaths rather than bullets. New crystalline habits were also observed, including hexagonal columns with scrolls growing along the prism faces. In addition to clearly defined crystal habits, complex polycrystals composed of planar and columnar components were also common. Facet hollowing is a feature common to most of the sampled crystals, with hollowing occurring even on the smallest facets. This result suggests that the effective density of cirrus ice crystals may be smaller than what is usually assumed in numerical cloud models. Recent laboratory measurements of ice crystals grown at the observed cirrus temperatures show similar morphologies, including frequent scroll growth. Laboratory measured growth time-series are used to inform ice microphysical models of the observed crystals. One-dimensional and three-dimensional large eddy simulations of the observed cases reveal that changes in crystal density based on measurements lead to the development of cirrus generating heads and fall streaks that are similar to the observed cases.