Characterization of Large Hailstone Growth Using Stable Isotopes

The stable isotope composition of a hailstone is related to the source and transport of moisture, atmospheric temperature, cloud droplet, and vapor conditions that occur at crystallization into ice. The isotope content of cloud water is preserved as it transitions from the liquid to solid phase on a hailstone. Water isotope fractionation therefore is an indicator for assessing flow path and accretion mechanisms of hail as it forms in supercell thunderstorms. The stable isotope values such as δD can be used as indicator of cloud temperature and therefore altitude of hailstone formation. δD values obtained from the layers across a hailstone section therefore aid in defining the origin and trajectory of the hailstone through the storm event. Two separate hail events at Burkburnett and Del Rio, Texas in the spring of 2020, both provided greater than 5 cm (2 inch) diameter hailstone samples in this study. Sixteen hailstones from these two events have been dissected at nominal 0.5 cm intervals, providing 254 subsamples of melt water for isotopic analysis together with thin sections for ice structure analysis. Hailstone isotopic analysis with the ice structure microphotographs were used as proxies to determine the deposition of cloud water as a glaze layer was added. Results were compared to radar soundings of the two storms and made possible ground truthing of hail size and location estimates. The goal of this research is to provide better information on hail formation and growth within clouds that will contribute to storm prediction, warning and risk mitigation of hailstorms.