Measuring hail-like trajectories and growth with the Hailsonde

Abstract The broad spectrum of possible hailstone shapes and internal structures is a product of the complex interplay between hailstone growth physics, aerodynamics and in-storm conditions. As a result of this sensitivity, hailstone characteristics can be highly variable within a single deep convective cell. Recent progress on modeling individual hailstone trajectories and growth has benefited from new understanding of hail production processes; however, the representativeness remains uncertain. In-situ observations along hail-like trajectories have only now become possible thanks to the miniaturization of radiosonde electronics, which, when packaged into a durable probe of similar shape and size to large hailstones, can survive the conditions inside thunderstorms while behaving like hailstones. Trajectory and icing data from these hail-like probes provides invaluable information for assessing the aforementioned hail growth simulations. On 24 July 2023, two Hailsondes were launched four minutes apart into a supercell during the Northern Hail Project (NHP) in Alberta, Canada, with the storm producing large hail exceeding 50 mm (1.96 in) in maximum dimension during the flight. The vertical speed of both probes exceeded 37 m s −1 during balloon-assisted ascent, and, after the balloons detached, the probes continued to ascend to almost 8000 m AMSL. Despite travelling along similar trajectories, the sondes experienced different growth regimes. Investigation of polarimetric weather radar data shows changes in the probes’ pathways relative to the updraft and a column of enhanced specific differential phase (K DP ), indicating the first Hailsonde likely experienced a greater raindrop collection rate, contributing to the differences in icing conditions.