Collaborative Research: Challenges in Understanding Tornadogenesis and Related Phenomena

超级单体后侧翼下沉气流(RFD)与大的水平涡度有关，假设涡线在下沉气流周围形成环状。在某些条件下，这些环可以在相邻的上升气流中向上拉起，在下降气流的一侧形成涡线拱形。这是一种简洁的方式来描述一对反向旋转的涡旋，它们横跨与垂直速度的大梯度相关的水平涡度区域。龙卷风的发生偶尔发生在涡旋对的气旋成员中。拱化过程被认为至少以两种方式依赖于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的负浮力可能大到足以导致涡环在地面简单地展开，从而排除拱化过程。在这项研究中，将采用互补的观测和理想化的数值模拟、理论方法来研究这一问题。智力上的优点：超级细胞龙卷风的发生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尾随的RFD之间的水平涡度。反过来，RFD似乎部分是超级单体特有的小尺度降水结构的结果：钩状回波和/或一个狭窄的下降反射率核心。在一些超级单体中，主要垂直气流之间产生的涡度在上升气流中向上拉升，导致后翼阵风锋汇合区出现拱形涡线和相关的反旋转涡旋。在某些条件下，似乎受负浮力的影响，龙卷风可能发生在对转对的气旋成员附近。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侧下沉气流浮力、龙卷风气旋成因和龙卷风发生。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。通过利用具有双极化分集能力的多普勒雷达诊断后侧降水厚度和水流星结构，可以直接将对RFD浮力和龙卷风气旋成因的新认识用于龙卷风警报过程。此外，预计可以通过低层热力学层结的知识来估计RFD浮力。最终，业务气象学家可能会更好地区分潜在的龙卷风超级单体和非龙卷风超级单体。传统上，首席PI(Rasmussen)一直积极通过研讨会将新知识直接传递给国家气象局和其他预报组织。此外，所有合作的私人投资机构都参加会议，并邀请研讨会交流新的知识。这些类型的外联工作计划继续下去。资金将支持一名女性研究人员和一名女性学生，这将有助于留住女性从事科学工作，并促进多样性。

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.