Abstract
On 9 June 2009, the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) sampled a supercell as it traversed through an increasingly stable environment with decreasing bulk shear and storm-relative helicity. To investigate the impacts of the observed environmental heterogeneity on storm morphology, a series of idealized simulations were conducted. Utilizing the base-state substitution modeling technique, the separate effects of the changing wind profile and the increasingly stable boundary layer were evaluated. The varying base-state environment in each experiment elevated the mean source region of updraft parcels. These elevated parcels were drier (with less instability), and more negatively impacted by entrainment. Thus, as the updraft ingested a larger fraction of elevated parcels, its buoyancy was depleted, leading to demise. Unsurprisingly, the increasingly stable low-level environment played a dominant role in this process; however, wind profile modifications also elevated the mean source region of updraft parcels, which independently impacted storm strength and morphology. Changes to the storm’s internal dynamical processes were assessed using the diagnostic pressure equation. The evolution in total vertical acceleration was primarily related to changes in accelerations that were connected to updraft rotation, as well as shifts in buoyancy. The dynamical accelerations weakened and became maximized at a different altitude, resulting in an increasingly elevated updraft parcel source region. Overall, this study finds that a shifting updraft parcel source region can significantly impact storm maintenance; importantly, such a shift can result from changes in environmental temperature, moisture, or wind profiles.
