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.

本研究的重点是在龙卷风旋转起源验证实验II （VORTEX2）中观测到的与超级单体雷暴相关的壁云的形成和结构。这项研究将通过对超级单体钩区进行摄影测量分析的照片和高清视频进行分析来完成，这些照片和高清视频也同时被移动多普勒雷达扫描。将视觉数据与超级单体钩区高分辨率单多普勒和双多普勒分析相结合，将实现以下目标。地面速度跟踪显示（GBVTD）技术将用于获得具有良好视觉数据和仅用一个雷达覆盖的风暴的轴对称风场。探空、移动中网和地面站数据也将被纳入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年前发表的理想化数值模拟和目视观测。将测试三个假设。首先，超级单体阵风锋后面的低层空气被吸收到上升气流中，并在比主云底部更低的高度饱和。其次，壁云是由绝热冷却形成的，这种绝热冷却与可能存在于壁云中的循环所产生的压力不足有关。第三，壁云的形成是由于上升的低层飞毛腿附着在主云基础上。第二个目标是记录龙卷风和非龙卷风壁云的降水（反射率）、涡度、垂直运动、扰动压力、角动量和水平风场的三维结构。该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。它还将有助于确定相对于上升气流、低层中气旋和低降水、经典降水和高降水超级单体在VORTEX2期间取样的钩区内降水分布的壁云的规模和强度之间的关系。最后，将有可能将壁云的视觉特征与多普勒雷达数据得出的运动结构进行比较。智力优势：在许多观测研究中，与超级单体雷暴有关的壁云已经被直观地记录下来。它通常被认为与低层上升气流有关，并且经常是龙卷风形成的位置。令人惊讶的是，迄今为止还没有任何观测研究系统地研究了壁云的形成、结构和与低层上升气流、中气旋和降水分布有关的演变。因此，实现上述目标将增强我们对超级单体雷暴的低层视觉结构和演化的基本理解。更广泛的影响：预计这项研究的结果将被纳入国家气象局的天空预警风暴观测者训练。在恶劣天气情况下，天空预警观测员对准确传播视觉天气信息至关重要。该项目将使许多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课程。