Environment and storm-scale influences on supercell updraft characteristics
Supercells are a special class of thunderstorms with a single, rotating updraft that have the propensity to produce severe weather, such as large hail, damaging winds, and/or tornadoes. A change in wind speed and/or direction with height (i.e., vertical wind shear; hereafter simply “shear”) has long been thought to affect supercells by horizontally displacing updraft hydrometeor mass downstream, thereby facilitating storm longevity. Shear also impacts the size of supercell updrafts, with stronger shear leading to wider, less dilute, and stronger updrafts with greater hydrometeor production. To more clearly define the role of shear across different vertical layers on hydrometeor concentrations and displacements relative to supercell updrafts, a suite of idealized Cloud Model 1 (CM1) simulations was conducted. Shear magnitudes were systematically varied across the 0-1 km, 1-6 km, and 6-12 km layers while the thermodynamic environment was held fixed. Simulations show that as shear magnitude increases, especially between 1-6 km, updrafts become wider and less dilute with an increase in hydrometeor loading, along with an increase in precipitation area/rate and total precipitation accumulation. Even with greater updraft hydrometeor loading amid stronger shear, updrafts are more intense in stronger shear simulations due to both larger thermal buoyancy (owing to wider, less diluted updraft cores) along with stronger dynamic perturbation pressure gradient accelerations. Furthermore, hydrometeor mass is displaced farther downstream in simulations with stronger 1-6 km shear. In contrast, there is less sensitivity of hydrometeor concentrations and displacements to variations in either 0-1 km or 6-12 km shear. Results are consistent across free tropospheric relative humidity sensitivity simulations, which show an increase in updraft size and hydrometeor loading with increasing free tropospheric relative humidity owing to a reduction in entrainment-driven dilution for wider updrafts in moister environments. These findings will help to advance our understanding of the environment and storm-scale influences on this special class of severe thunderstorms, and therefore, will hopefully lead to improvements in supercell forecasting. In addition, highlights from Dr. Mulholland’s research group related to and extending this work with radar observations will be briefly shown and discussed.
Bio: Jake Mulholland is currently a tenure-track assistant professor in the Department of Atmospheric and Environmental Sciences at the University at Albany. Before starting his position at Albany in fall 2024, Mulholland was formally a tenure-track assistant professor (2022-2024) in the Department of Atmospheric Sciences at the University of North Dakota in Grand Forks, ND, and was a research faculty associate (2021-2022) and a National Research Council postdoctoral fellow (2019-2020) in the Department of Meteorology at the Naval Postgraduate School in Monterey, CA. He obtained both his Ph.D. (2016-2019) and M.S. (2014-2016) degrees in atmospheric sciences from the University of Illinois Urbana-Champaign, and his B.S. (2010-2014) degree in meteorology from the State University of New York at Oswego.
His research interests include severe thunderstorms with a special emphasis in simulating these storms with high-resolution numerical models to better understand how changes in the environment alter storm-scale properties (such as entrainment and dilution, updraft size and strength, among others). Mulholland has played an integral role in both national and international field campaigns studying phenomena such as lake-effect snowstorms, terrain-forced thunderstorms, and shallow post-cold-frontal thunderstorms over the Pacific Ocean. Mulholland has also led or co-led multiple storm chasing courses at UND, SUNY Oswego, and UIUC. Mulholland was awarded UND’s student-voted “Best Academic Advisor Award” and student/staff/faculty-voted “Above and Beyond Award” and continually strives to make his research and classes easily accessible to a diverse audience.