Numerical Investigation of Damaging Wind Mechanisms within Bow Echoes

最近的观测研究表明，在弓形回波阵风锋上形成的低层（0-5 km AGL）、小尺度（1-10 km）“中涡旋”在产生直线和龙卷风风害中起着重要作用。研究表明，中涡旋能够产生长而窄的直线风损带，这在以前被认为是由下降的后方流入射流造成的。此外，中涡旋已被证明在弓形回波中产生最强烈的损害。然而，这些涡旋的形成机制尚不清楚。因此，本研究的第一个目标是研究产生这些漩涡的过程。第二个目标是更好地理解控制中涡旋强度的动力学过程。在弓形回波中观察到涡旋强度的光谱，这样一些具有破坏性，而另一些则没有。通过分析观测到的弓形回波事件的数值模拟，可以实现上述目标，其中“中涡旋”与龙卷风一起产生了最强烈的直线风损害。模拟将由高级研究天气预报模式（ARW）进行。使用嵌套网格配置，ARW将具有足够的空间分辨率来模拟系统尺度弓形回波属性以及子系统尺度中涡旋。将进行一些灵敏度实验，以检查模型解对初始化、环境条件和ARW内可用的各种物理选项的依赖。智力价值：研究目标将进一步了解产生破坏性地面风的弓回波中的重要动力学过程。中涡旋能够产生长而窄的直线风损伤，这一观点挑战了长期存在的概念模型，即弓形回波顶点的下降后方流入射流是弓形回波内大部分直线风损伤的原因。因此，了解中涡旋的形成机制以及控制其强度的动力学过程对于完善回波风损伤是如何以及在何处产生的概念模型非常重要。更广泛的影响这项研究的结果可能通过改善对由弓形回波产生的破坏性地面风的警告，提供重要的社会效益。通过了解中涡旋是如何形成的，有可能预测随着弓形回波的演变，破坏性风将在何时何地产生。为了最大限度地减少误报警率，区分较强的破坏性涡旋和较弱的非破坏性环流也很重要。本研究将使本科生接触到研究过程。这种研究经验提供了一个经验学习的机会，这是宝贵的，因为他们认为在大气科学的职业选择。他们还将获得运行最先进的中尺度模型的经验。在林登州立学院开展ARW不仅将加强校园研究基础设施，而且将在本科课程的许多课程中用作强大的教学工具。

Recent observational studies have documented the important role that low level (0-5 km AGL), small scale (1-10 km) "mesovortices" formed on the gust front of bow echoes play in producing both straight line and tornadic wind damage. It has been shown that mesovortices are capable of producing long, narrow straight-line wind damage swaths that have previously been attributed to a descending rear inflow jet. Further, mesovortices have been shown to produce the most intense damage within bow echoes. Yet, the genesis mechanism for these vortices is not well understood. The first objective of this research is, therefore, to examine the processes that create these vortices. A second objective is to better understand the dynamical processes that govern mesovortex strength. A spectrum of vortex strengths has been observed within bow echoes such that some are damaging while others are not. The objectives will be met by analyzing numerical simulations of an observed bow echo event where "mesovortices" produced the most intense straight-line wind damage along with tornadoes. The simulations will be produced by the Advanced Research Weather and Forecasting Model (ARW). Using a nested grid configuration, the ARW will have adequate spatial resolution to simulate the system-scale bow echo attributes along with sub-system scale mesovortices. A number of sensitivity experiments will be run to examine the model solution dependence on the initialization, environmental conditions, and various physics options that are available within the ARW.Intellectual Merit: The research objectives will further fundamental understanding of the important dynamical processes within bow echoes that produce damaging surface winds. The idea that mesovortices are capable of producing long, narrow swaths of straight-line wind damage challenges the long standing conceptual model that a descending rear inflow jet at the apex of the bow echo is responsible for much of the straight-line wind damage within bow echoes. Thus, it is important to understand the mesovortex genesis mechanism along with the dynamical processes that govern their strength in an effort to refine the conceptual model of how and where within bow echoes wind damage is produced. Broader Impacts The outcomes of the research may provide an important societal benefit by improving warnings for damaging surface winds produced by bow echoes. By understanding how mesovortices form, it may be possible to anticipate where and when damaging winds will be produced as the bow echo evolves. To minimize the false alarm rate, it will also be important to discriminate between the stronger damaging vortices and the weaker non damaging circulations. This research will expose undergraduate students to the research process. This research experience affords an experiential learning opportunity that is invaluable as they think about career options within the Atmospheric Sciences. They will also gain experience running a state-of-the-art mesoscale model. Having the ARW running at Lyndon State College will not only enhance the on campus research infrastructure but will also be used as a powerful teaching tool in many courses within the undergraduate curriculum.