Collaborative Research: Propagation, Evolution and Rotation in Linear Storms (PERiLS)

危（线性风暴的传播、演变和旋转）项目将把美国国家科学基金会和美国国家海洋和大气管理局的科学家聚集在一起，研究美国东南部的恶劣天气。在美国东南部，恶劣天气经常是由飑线产生的，也被称为准线性对流系统（QLCSs）。在美国，大约四分之一的龙卷风是由QLCS造成的，大多数QLCS龙卷风发生在美国东南部，由QLCS产生的龙卷风对生命和财产构成了重大威胁，但预测QLCS龙卷风事件仍然面临着重大挑战，甚至比预测超级单体龙卷风还要困难。目前的天气观测网络没有很好地观测到导致这些危害的小尺度过程和精确环境，对QLCS龙卷风形成过程也缺乏了解。更复杂的是，粗糙的数据和预测分析表明，沿qlcs的大片地区可能有利于龙卷风的形成，但龙卷风往往只发生在该地区的一小部分。虽然许多实地活动都集中在更好地了解超级单体龙卷风形成（特别是在大平原），但没有活动专门集中在收集数据以了解QLCS龙卷风形成。从2021年开始，“危险”将是第一个这样的项目，并将在美国东南部部署一个广泛的尖端观测系统网络，以收集数据，帮助研究人员更好地了解龙卷风在美国东南部是如何形成的，龙卷风的前兆是什么，以及风暴过程和特征可以用来区分将产生强风的风暴和将产生龙卷风的风暴。关于QLCS龙卷风是如何形成的，我们的知识有很大的空白，必须在提高预报技能之前加以解决。QLCS龙卷风通常在中涡旋中形成，但大多数中涡旋不会产生龙卷风。“高切变”和“低cape”环境在美国东南部普遍存在；在这些环境中形成的风暴占该地区强风和龙卷风报告的很大一部分。这个环境如何特别支持QLCS龙卷风形成尚不清楚。此外，风暴和环境的时空变化特征尚未得到很好的量化。虽然已有基于QLCS龙卷风业务数据的理想化数值模拟研究和气候学，但缺乏表征风暴和次风暴尺度过程以及风暴特征与快速演变的近风暴环境的相互作用所必需的精细尺度观测。危场活动将获得解决以下相关目标所需的观察结果：(1)确定低层中涡旋形成的机制；2)识别龙卷风和非龙卷风QLCS中涡旋的特征和机制；3)识别与QLCS中涡旋和龙卷风形成相关的环境变异性和风暴-环境相互作用；4)表征冷锋过程与系统产生的冷池在强强迫qcs演变中的作用。这一前所未有的数据集将有助于理解环境和风暴内部过程之间的相互作用，这些过程有助于QLCS龙卷风的形成。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The PERiLS (Propagation, Evolution and Rotation in Linear Storms) project will bring together NSF and NOAA scientists to study severe weather in the Southeastern U.S. In the Southeastern U.S., severe weather is frequently produced by squall lines, also known as quasi-linear convective systems (“QLCSs”). QLCSs are responsible for approximately a quarter of all tornadoes in the U.S. and the majority of QLCS tornadoes occur in the Southeastern U.S. QLCS-spawned tornadoes pose a significant threat to lives and property, but forecasting QLCS tornado events continues to pose significant challenges, even more so than forecasting supercell tornadoes. The small-scale processes and precise environments leading to these hazards are not well observed by the current operational weather observing network and there is a lack of understanding of QLCS tornadogenesis processes. Complicating this further, coarse data and forecast analyses suggest large areas along QLCSs may be favorable for tornadogenesis (tornado formation), but tornadoes tend to occur only within a small fraction of that area. While many field campaigns have focused on a better understanding of supercell tornadogenesis (especially in the Great Plains), no campaigns have focused specifically on collecting data to understand QLCS tornadogenesis. Starting in 2021, PERiLS will be the first such project, and will deploy an extensive network of cuttingedge observing systems to the Southeastern U.S. to gather data to help researchers better understand how tornadoes form in QLCSs, what are the precursors for tornadoes, and what storm processes and characteristics can be used to differentiate storms that will produce severe winds from those that will produce tornadoes.There are critical gaps in our knowledge concerning how QLCS tornadoes form, which must be addressed before forecast skill can be improved. QLCS tornadoes often form within mesovortices, but most mesovortices do not produce tornadoes. Environments with “high-shear” and “low-CAPE” are prevalent in the SE U.S.; storms that form in these environments account for a substantial fraction of severe wind and tornado reports in the region. How this environment specifically supports QLCS tornadogenesis is unknown. Moreover, the characteristics of the temporal and spatial variability, of both the storm and the environment, has yet to be well quantified. While there have been idealized numerical modeling studies and climatologies based on operational data of QLCS tornadoes, there is a dearth of the fine-scale observations that are necessary to characterize storm and sub-storm scale processes and the interaction of storm features with the rapidly-evolving near-storm environment. The PERiLS field campaign will obtain observations needed to address the following interrelated objectives: (1) Identify the mechanisms for low-level mesovortex formation; 2) Identify the characteristics and mechanisms that distinguish tornadic from non-tornadic QLCS mesovortices; 3) Identify the environmental variability and storm-environment interactions that are associated with QLCS mesovortex and tornado formation; and 4) Characterize the roles of cold frontal processes vs. system-generated cold pools in the evolution of strongly-forced QLCSs. This unprecedented data set will facilitate an understanding of the interplay between environmental and within-storm processes that contribute to QLCS tornadogenesis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.