Hailstone Stable Isotope Measurements as Indicators of Hail Growth Mechanisms in a Texas Hailstorm

Abstract There are numerous gaps in our understanding of hailstone formation and growth evolution, which are otherwise difficult to acquire. To date, few studies have investigated the temperature of origin of hail embryos and hailstone trajectories. Hailstone trajectories were deduced from isotopic compositions combined with crystal structures in this study. These data could be integrated with radar observations to improve our understanding of the atmospheric conditions and cloud structures for hailstorms. On the evening of 12 April 2016, a supercell thunderstorm produced a large swath of giant hail across the northern portions of the city of San Antonio, Texas. We collected and documented ten hailstones, displaying characteristics of conical, spheroidal and irregular shapes, clear and cloudy ice, fine and coarse ice textures. Isotopic analysis of 117 hailstone subsamples, together with their crystal structures, are examined here to provide information on the temperature of clouds in which hailstone layers formed. Based on the deduced hailstone trajectories, we proposed two distinct hailstone growth models based on the origin of the embryos: hailstones with clear embryos forming at low levels show recirculation with an up-and-down cycle, while those with cloudy embryos forming at high levels have simpler downward trajectories. The derived hailstone trajectories are consistent with radar and atmospheric sounding observations, confirming the effectiveness of isotopic analysis in tracing hailstone growth paths. Our findings provide new insights into the complex growth processes of hailstones and their trajectories within supercell thunderstorms.