13B.1 What Is the Role of the Gust Front in Tornadogenesis?

Thursday, 25 October 2018: 2:00 PM
Pinnacle AB (Stoweflake Mountain Resort )
Adam L. Houston, Univ. of Nebraska−Lincoln, Lincoln, NE; and C. C. Weiss, B. Argrow, and E. W. Frew

What is the role of the gust front in tornadogenesis? Is it merely a passive feature advected in the circulating airflow beneath a supercell or are the source and amplification of circulating air that lead to tornadogenesis dependent upon these boundaries? Tornadogenesis can emerge in axisymmetric models without boundaries but these models generally fail to represent the expected asymmetric sources of angular momentum tied to storm-generated airmasses beneath a supercell. Does this asymmetry merely associate to the existence of boundaries prior to tornadogenesis or is the unique structure of boundaries which can be dynamically favorable for tornadogenesis important? Perhaps, in an asymmetric field of angular momentum, boundaries are required to consolidate vorticity beneath the updraft; a possibility which raises an ancillary question: what role is played by the low-level updraft in consolidating rotation? Is the gust front or the updraft more important in this consolidation? Ostensibly, the relationship is synergistic: the updraft promotes consolidation along the gust front.

This presentation will summarize prior work that addresses these complex interactions and offers results from a theoretical study that attempts to provide some insight. These experiments use the Coriolis force as background angular momentum that can be converged beneath a parameterized updraft, thereby decoupling the source of angular momentum from the base state environment and storm-generated outflow. Experiments involve a parameter space defined by the Coriolis parameter, strength of the low-level updraft, and height of the updraft base. A gust front is introduced into each simulation and the generation of near-surface rotation beneath the rotating parent updraft is assessed. The role of the storm updraft on low-level ascent (a proxy for stretching and tilting) relative to the role of the gust front on low-level ascent is quantified. The importance of gust front inflection is also considered along with the possible synergistic impact of the storm’s updraft on the inflection. Where possible, available observations across airmass boundaries beneath supercells are considered to complement the findings from these experiments.

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