Formation and Structure of Wall Clouds Observed During VORTEX2

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This research focuses on the formation and structure of wall clouds associated with supercell thunderstorms that were observed during the Verification of the Origins of Rotation in Tornadoes Experiment II (VORTEX2). The study will be accomplished through analysis of photogrammetrically analyzed photos and high-definition video of the hook region of supercells that were also concurrently being scanned by mobile Doppler radars. The objectives below will be met by integrating the visual data with high-resolution single and dual-Doppler analyses of the supercell hook region. The Ground Based Velocity Track Display (GBVTD) technique will be used to obtain axisymmetric wind fields for storms with good visual data and coverage with only one radar. Sounding, mobile mesonet, and surface station data will also be incorporated to document the thermodynamic characteristics of the environment and supercell hook region.The first objective is to understand the processes responsible for wall cloud formation.Current understanding of wall cloud formation is based on idealized numerical simulations published more than 25 years ago and visual observations. Three hypotheses will be tested. The first is that lower èe air behind the supercell gust front is ingested into the updraft and saturates at a lower altitude than the primary cloud base. Second, the wall cloud is formed by the adiabatic cooling associated with the pressure deficit created by circulation that may be present in the wall cloud. Third, wall cloud formation is due to rising low-level scud that attaches to the primary cloud base.The second objective is to document the three-dimensional structure of the precipitation (reflectivity), vorticity, vertical motion, perturbation pressure, angular momentum, and horizontal wind fields within tornadic and non tornadic wall clouds. This analysis will, for the first time, document the differences and/or similarities between tornadic and nontornadic wall clouds. It will also help to define the relationship between the scale and intensity of the wall cloud relative to the updraft, low-level mesocyclone, and precipitation distribution within the hook region for lower precipitation, classic, and high precipitation supercells sampled during VORTEX2. Finally, it will be possible to compare the visual characteristics of the wall cloud with the kinematic structure derived from the Doppler radar data.Intellectual Merit: The wall cloud associated with supercell thunderstorms has been visually documented in many observational studies. It is generally accepted to be associated with the low-level updraft and is often the location of tornadogenesis. Amazingly, no observational study to date has systematically examined wall cloud formation, structure, and evolution relative to the low-level updraft, mesocyclone, and precipitation distribution within the hook region. Hence, realizing the above stated objectives would enhance our fundamental understanding of the low-level visual structure and evolution of supercell thunderstorms.Broader Impacts: It is anticipated that results from this research will be incorporated into the National Weather Service Skywarn storm spotter training. Skywarn spotters are vital to the accurate dissemination of visual weather information during severe weather situations. The project will expose a number of undergraduate students to the research process and will enhance the research infrastructure (also used in teaching) at Lyndon State College. Research results will be incorporated into many of the undergraduate classes.