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

PERiLS（线性风暴中的传播、演变和旋转）项目将汇集NSF和NOAA的科学家，研究美国东南部的恶劣天气。恶劣天气通常由飑线（也称为准线性对流系统（“QLCS”））产生。QLCS造成了美国大约四分之一的龙卷风，大多数QLCS龙卷风发生在美国东南部，QLCS产生的龙卷风对生命和财产构成了重大威胁，但预测QLCS龙卷风事件仍然构成重大挑战，甚至比预测超级单体龙卷风更困难。小规模的过程和精确的环境，导致这些危险是没有很好地观察到目前的业务天气观测网络，并缺乏了解QLCS龙卷风的过程。更复杂的是，粗略的数据和预测分析表明，沿着沿着QLCS的大面积区域可能有利于龙卷风的形成，但龙卷风往往只发生在该区域的一小部分。虽然许多实地活动都集中在更好地了解超级单体龙卷风（特别是在大平原），没有活动专门集中在收集数据，以了解QLCS龙卷风。从2021年开始，PERiLS将成为第一个这样的项目，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如何在QLCS中形成，龙卷风的前兆是什么，以及什么样的风暴过程和特征可以用来区分会产生强风的风暴和会产生龙卷风的风暴。我们对QLCS龙卷风如何形成的知识存在重大差距，必须在提高预报技能之前解决这一问题。QLCS龙卷风通常在中涡旋内形成，但大多数中涡旋不会产生龙卷风。具有“高剪切”和“低CAPE”的环境在美国东南部是普遍的;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。这种环境如何特别支持QLCS龙卷风的发生尚不清楚。此外，风暴和环境的时间和空间变异性的特点还有待很好地量化。虽然已经有理想化的数值模拟研究和基于QLCS龙卷风业务数据的气候学，但缺乏表征风暴和亚风暴尺度过程以及风暴特征与快速演变的近风暴环境相互作用所需的精细尺度观测。PERiLS实地活动将获得解决以下相关目标所需的观测结果：（1）确定低层中涡旋形成的机制;（2）确定区分龙卷风和非龙卷风QLCS中涡旋的特征和机制;（3）确定与QLCS中涡旋和龙卷风形成有关的环境变率和风暴-环境相互作用;（4）分析冷锋过程和冷池在强强迫QLCS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过程之间的相互作用，有助于QLCS tornadogenesics.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.