Controls of Quasi-linear Convective System Tornado Intensity

Abstract:

Although tornadoes produced by quasi-linear convective systems (QLCSs) generally are weak and short-lived, they have high societal impact due to their proclivity to develop over short time scales, within the cool season, and during nighttime hours. Precisely why they are weak and short lived is not well understood, although recent work suggests that QLCS updraft width may act as a limitation to tornado intensity (Trapp et al. 2017, 2018; Marion et al. 2019). Herein, idealized simulations of tornadic QLCSs are performed using Cloud Model 1 (CM1) with variations in hodograph shape and length as well as initiation mechanism to determine the controls of tornado intensity.

Eight simulations QLCSs produce a total of 34 tornado-like vortices (TLVs). As found previously for supercells, the width of rotating updrafts in QLCSs serves as one of the primary limitations on TLV width and intensity; low-level updraft strength, updraft tilt, and updraft depth serve as secondary limits on TLV intensity. Additional analysis reveals that QLCS cold pools play a direct role in the development of a strong low-level forcing for ascent leading to tornado development, despite the cold pool’s potential deleterious effects on the storm’s low-level updraft and near-surface rotation. Nonetheless, the negative impacts of the QLCS cold pool ultimately limit the persistence of rotating updraft cores in the QLCS.