Numerical Investigation of Damaging Wind Mechanisms within Bow Echoes

近年来的观测研究表明，低层（0-5 km AGL）、小尺度（1-10 km）的中尺度涡在产生直线风和龙卷风中起着重要作用。 它已被证明，中涡能够产生长，窄的直线风破坏带，以前被归因于一个下降的后方流入射流。 此外，中涡旋已被证明在弓形回波中产生最强烈的破坏。 然而，这些漩涡的成因机制还没有很好的理解。 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了解支配中涡强度的动力过程。 在弓形回波中观察到了一系列涡旋强度，其中一些具有破坏性，而另一些则没有。将通过分析观测到的弓形回波事件的数值模拟来实现这些目标，在弓形回波事件中，“中涡”产生了最强烈的直线风破坏沿着龙卷风。 这些模拟将由高级研究天气和预报模型（ARW）产生。 使用嵌套网格配置，ARW将有足够的空间分辨率来模拟系统尺度弓形回波属性沿着与子系统尺度中涡旋。 一些敏感性实验将运行，以检查模型的解决方案依赖于初始化，环境条件，和各种物理选项，可在ARW.Intellectual优点：研究目标将进一步从根本上了解弓回波内产生破坏性的表面风的重要动力学过程。 中涡能够产生长而窄的直线风害的想法对长期存在的概念模型提出了挑战，该模型认为，弓形回波顶点处的下降后部入流射流是弓形回波内大部分直线风害的原因。 因此，重要的是要了解中涡的生成机制，沿着的动力过程，在努力完善的概念模型，如何以及在弓回波风损害的产生。更广泛的影响研究的结果可能会提供一个重要的社会效益，通过改善警告破坏性的表面风所产生的弓形回波。 通过了解中涡旋是如何形成的，随着弓形回波的发展，有可能预测破坏性的风将在何时何地产生。 为了使假警报率最小化，区分较强的破坏性涡旋和较弱的非破坏性环流也很重要。这项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体验式学习的机会，这是非常宝贵的，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。 在林登州立学院运行ARW不仅将增强校园研究基础设施，而且还将用作本科课程中许多课程的强大教学工具。

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.