Formation and Structure of Wall Clouds Observed During VORTEX2

VORTEX2 期间观测到的壁云的形成和结构

• 批准号: 1242339
• 负责人: Nolan Atkins
• 金额: $ 23.43万
• 依托单位: Lyndon State College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-02-01 至 2018-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1242339&HistoricalAwards=false
• 关键词: Formation; Structure; Wall; Clouds; Observed

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.

这项研究的重点是在龙卷风实验II(VORTEX2)中观测到的与超级单体雷暴有关的壁云的形成和结构。这项研究将通过分析摄影测量分析的照片和超级细胞钩区的高清晰度视频来完成，这些照片和视频也同时被移动多普勒雷达扫描。下面的目标将通过将视觉数据与对超级细胞钩区的高分辨率单多普勒和双多普勒分析相结合来实现。地面速度轨迹显示(GBVTD)技术将用于获得具有良好视觉数据和覆盖范围的轴对称风暴风场，只需一台雷达。探测、流动中云和地面站数据也将被用来记录环境和超级单体钩区的热力学特征。第一个目标是了解壁云形成的过程。目前对壁云形成的理解是基于25年前发表的理想化的数值模拟和目视观测。三个假说将被检验。首先，超级单体阵风锋面后面的低层空气被吸入上升气流，并在比主要云底更低的高度饱和。第二，壁云是由绝热冷却形成的，而绝热冷却与可能存在于壁云中的环流产生的压力差有关。第二个目标是记录龙卷风和非龙卷风壁云中降水(反射率)、涡度、垂直运动、扰动气压、角动量和水平风场的三维结构。这项分析将首次记录龙卷风和非龙卷风壁云之间的差异和/或相似之处。它还将有助于确定VORTEX2期间采集的低降水、经典和高降水超级单体的壁云相对于上升气流、低层中气旋的规模和强度与钩区内降水分布之间的关系。最后，可以将壁云的视觉特征与从多普勒雷达数据得出的运动结构进行比较。智慧的优点：在许多观测研究中，与超级单体雷暴有关的壁云已经被可视化地记录下来。人们普遍认为它与低层上升气流有关，通常是龙卷风发生的地方。令人惊讶的是，到目前为止，还没有观测研究系统地研究壁云的形成、结构和演变与低空上升气流、中气旋和钩区内降水分布的关系。因此，实现上述目标将加强我们对超级单体雷暴低层视觉结构和演变的基本了解。布罗德影响：预计这项研究的结果将被纳入美国国家气象局天空警告风暴观测员培训。Skywarn观测员对于在恶劣天气情况下准确传播视觉天气信息至关重要。该项目将使一些本科生接触到研究过程，并将加强林登州立学院的研究基础设施(也用于教学)。研究成果将被纳入许多本科生班级。