Collaborative Research: Challenges in Understanding Tornadogenesis and Related Phenomena

合作研究：理解龙卷风发生及相关现象的挑战

• 批准号: 0733531
• 负责人: Erik Rasmussen
• 金额: $ 22.16万
• 依托单位: Rasmussen Systems LLC
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-15 至 2010-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0733531&HistoricalAwards=false
• 关键词: Collaborative; Research; Challenges; Understanding; Tornadogenesis

Supercell rear flank downdrafts (RFD) are associated with large horizontal vorticity, with vortex lines hypothesized to form rings around the downdraft. Under certain conditions, these rings can be drawn upward in an adjacent updraft, forming arches of vortex lines on one side of the downdraft. This is a compact way of describing a pair of counter-rotating vortices that straddle a region of horizontal vorticity associated with large gradients of vertical velocity. Tornadogenesis occasionally occurs in the cyclonic member of the vortex pair. The arching process is thought to depend on the RFD in at least two ways: 1) the negative buoyancy in the RFD generates the horizontal vorticity that is eventually tilted, forming the arches, and 2) the negative buoyancy of the RFD can be large enough to cause the vortex rings to simply spread at the ground, precluding the arching process. In this research, complementary observational and idealized numerical modeling, theoretical methods will be employed to study this problem.Intellectual Merit: Supercell tornadogenesis apparently is the result of a complex series of processes. Evidence suggests that the vorticity in a tornado originates as horizontal vorticity between the supercell updraft and a trailing RFD. The RFD, in turn, appears to be partially the result of small-scale precipitation structures unique to supercells: the hook echo and/or a narrow descending reflectivity core. In some supercells, the vorticity generated between the major vertical drafts is drawn upward in the updraft, leading to arched vortex lines and associated counter-rotating vortices in the rear flank gust front convergence zone. Under certain conditions, that appear to be governed by the degree of negative buoyancy in the RFD, tornadogenesis can occur in the vicinity of the cyclonic member of the counter-rotating pair. Utilizing a state-of-the-art observational analysis tool suite and a cloud model, this research will further understanding of rear flank downdraft buoyancy, tornado cyclone genesis, and tornadogenesis. Broader Impacts: This research has considerable value in the area of public safety. New understanding of RFD buoyancy and tornado cyclone genesis can be used directly in the tornado warning process by diagnosing rear-flank precipitation thickness and hydrometeor structure using Doppler radars with dual-polarization diversity capability. Further, it is anticipated that RFD buoyancy can be estimated through knowledge of the low-level thermodynamic stratification. Eventually, it is likely that operational meteorologists can make much better discriminations between potentially tornadic and non-tornadic supercells. Traditionally, the lead PI (Rasmussen) has been active in transferring new knowledge directly to National Weather Service and other forecasting organizations via seminars. Also, all of the co-PIs participate in conferences, and invited seminars to communicate new knowledge. These types of outreach work are planned to continue. Funding will support a female researcher and a female student, which should help facilitate the retention of women in science, as well as promote diversity.

超级单体后翼下沉气流（RFD）与大的水平涡量有关，假设涡线在下沉气流周围形成环。在某些条件下，这些环可以在相邻的上升气流中被向上拉，在下降气流的一侧形成涡线拱。这是一种描述一对反向旋转的涡的简洁方法，这对涡横跨与大的垂直速度梯度相关的水平涡度区域。涡旋对中的气旋成员偶尔也会产生龙卷风。旋转过程被认为至少在两个方面取决于RFD：1）RFD中的负浮力产生最终倾斜的水平涡度，形成拱形，2）RFD的负浮力可以足够大，导致涡环在地面简单地扩散，排除旋转过程。在本研究中，互补的观测和理想化的数值模拟，理论方法将被用来研究这个问题。 超级单体龙卷风的形成显然是一系列复杂过程的结果。有证据表明，龙卷风中的涡度起源于超级单体上升气流和拖尾RFD之间的水平涡度。RFD，反过来，似乎是部分的结果，小规模的降水结构独特的超级单体：钩回波和/或一个狭窄的下降反射率的核心。在某些超级单体中，主要垂直气流之间产生的涡量在上升气流中被向上拉，导致在后翼阵风锋会聚区中形成拱形涡线和相关的反向旋转涡。在某些条件下，这似乎是由在RFD的负浮力的程度，龙卷风发生可能发生在附近的反旋转对气旋成员。 利用最先进的观测分析工具套件和云模型，这项研究将进一步了解后翼下沉浮力，龙卷风气旋的成因和龙卷风的发生。更广泛的影响：这项研究在公共安全领域具有相当大的价值。 通过使用具有双极化分集能力的多普勒雷达诊断后翼降水厚度和水凝物结构，可以将对RFD浮力和龙卷风气旋成因的新认识直接用于龙卷风警报过程。此外，预计RFD浮力可以通过低层热力学分层的知识来估计。最终，业务气象学家可能会更好地区分潜在的龙卷风和非龙卷风超级单体。传统上，首席PI（拉斯穆森）一直积极通过研讨会直接向国家气象局和其他预报组织传授新知识。此外，所有共同PI都参加会议，并邀请研讨会交流新知识。计划继续开展这类外联工作。资金将用于支持一名女研究员和一名女学生，这将有助于促进妇女留在科学界，并促进多样性。