Exploration of relationships between the hail report sizes and the radar-derived convective features and atmospheric environments from ERA5 reanalysis: A study over the contiguous United States




Vasquez, Edward Raven

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Hail is a type of frozen precipitation that originates from cumulonimbus clouds with updraft velocities sufficient to suspend hailstones until the terminal velocity of the hail overcomes the updraft velocity. While larger hailstones have been studied extensively due to their significant economic impacts, small hail is also known to cause comparable impacts yet remain understudied due to report biases towards recording larger hail sizes. Consequently, the full spectrum of hail size properties, encompassing both the radar observations and the environmental conditions that produced hail reported at various sizes, is still to be assembled as a unified dataset. To fill this gap, we paired ground hail reports from National Centers for Environmental Information Storm Data, Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) and Meteorological Phenomena Identification Near the Ground (mPING) databases with the attributes of radar-derived convective features and the European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5) atmospheric vertical profiles to construct a rich dataset. Our study investigates how characteristics of radar reflectivity and atmospheric profiles are related to the size of hail reported over the Contiguous United States, where report density is the greatest and radar network coverage is robust. Convective features extracted from the Multi-Radar/Multi-sensor System (MRMS) allow comparable remote sensing observations of hailstorms. We evaluate the single-polarization radar reflectivity derived Maximum Expected Size of Hail (MESH) performance against reported hail sizes. ERA5 vertical atmospheric profiles are explored to form relationships between the thermodynamic environment including the derived convective indices, hodographs, and the hail sizes. The properties of convective systems and their dynamic and thermodynamic variables in three hail size categories are summarized. Major findings include: • Supplemental datasets, obtained through crowdsourcing and volunteer observers, provide small hail report sizes that align with the broader spectrum of hail properties. • MRMS MESH has some biases toward the reported hail size, as it tends to overestimate small hail and underestimate significant hail sizes. • Hodographs constructed from ERA5 reanalysis vertical wind profiles, composited by region, reveal an apparent increase in low-level streamwise vorticity with increasing hail size. Additionally, regional variations of thermodynamic properties for reported hail events are found in the Contiguous United States. These results provide insights into the relationships between radar observations and atmospheric environments and the sizes of hail, including small hailstones that are often overlooked in previous studies.


A Thesis Submitted In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in Environmental Science from Texas A&M University-Corpus Christi.


CoCoRaHS, ERA5, hail, mPING, MRMS, radar



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