Tracing Hailstone Development: Isotopic Evidence and Microphysical Variability in Texas Supercell Events

Abstract

Two supercell thunderstorms that occurred in Del Rio and Burkburnett, Texas in the spring of 2020 produced greater than 5 cm diameter hailstones. Fourteen hailstones, eight from Del Rio and six from Burkburnett, were cut in half along the maximum principal axis. Half the hailstone was dissected at 0.5 cm increments, providing 198 subsamples of meltwater (0.25 ml) for stable isotope analysis (ẟ ² H and ẟ ¹⁸ O) using a Picarro L2130‐i water analyzer and half used to create a thin section for identification and analysis of ice crystal morphology. Deuterium serves as a proxy for relative altitude, providing a record of hailstone formation and growth trajectory, while crystallographic analysis differentiates wet and dry growth. Results indicate significant variations in isotopic composition and ice crystal morphology, reflecting distinct growth trajectories in the supercell environment, providing evidence that hailstone formation and growth occurred at varying altitudes and reflect recycling in the updraft. The formation of a hailstone embryo at higher altitudes challenges the paradigm of embryo formation only at the cloud base or lower altitudes compared to the outer growth layers. Dendritic crystal morphologies observed in Del Rio hailstones are consistent with rapid freezing in the presence of elevated supercooled liquid water content. Mass ratio analysis provided that most of the hailstones approached the density of bubble free ice while the sphericity index reflected that most hailstones approached 0.80 sphericity but can more accurately be described as triaxial ellipsoids. The goal of this research was to provide better information on hailstone growth and trajectory through supercell convective thunderstorms.