The Vorticity Dynamics of Tornadoes: Formation and Maintenance Mechanisms

几十年来对龙卷风的研究在理解龙卷风如何在超级单体雷暴中形成方面取得了重大进展。然而，仍然有一些重要的问题没有得到确凿的答案。该奖项将涉及与通过使用复杂的数值模型发展和维持强大的近地自转有关的过程。这项工作的下游影响与提高天气预报员提供更准确的龙卷风活动警告的能力有关。该奖项还为培训一名博士后研究人员和扩大公众对科学的理解提供资金。该项目的目标是分析导致龙卷风加强和维护的各种机制。研究小组计划开发一种改进的龙卷风发生理论，并证明环境风廓线和龙卷风旋转之间的直接联系。这项研究追求两个目标。第一个是与研究小组最近发现的近地涡度动力学转变过程中涡旋的加强有关，第二个是探索龙卷风直接利用环境涡度的可能性。该项目将以模型为基础，使用50米分辨率的CM1数值模式模拟龙卷风，使用100米分辨率的超级单体模拟。将讨论六种假设，4种与龙卷风增强有关，2种与涡度的环境来源有关：·向自上而上机制的转变导致涡旋的快速增强。·这种转变伴随着涡旋尺度的反馈循环。·转变是否发生取决于初始涡团的强度。·一旦自上而上机制激活，垂直涡度的流入不再需要(但不是有害的)涡旋维持。然而，垂直涡度的持续涌入可能会影响涡旋的直径和强度。·在相关地块的起点高度存在较大的环境风暴相对流向涡度的情况下，正压涡度加强或有时主导通过地面阻力和斜压作用产生的水平近地涡度。·在相关地块的原点高度存在环境风暴相对横向涡度的情况下，正压涡度削弱了由地表阻力和斜压产生的水平近地涡度。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，认为值得支持。

Decades of research on tornadoes has resulted in significant progress in the understanding of how tornadoes form in supercell thunderstorms. However, there are still important questions that have not been answered conclusively. This award will address processes that are related to the development and maintenance of strong near-ground rotation though the use of sophisticated numerical models. The downstream impact of the work is related to improving the ability of weather forecasters to provide more accurate warnings of tornadic activity. The award also provides funding for the training of a postdoctoral researcher and outreach to enhance public understanding of science.The goal of this project is to analyze the various mechanisms that lead to tornado intensification and maintenance. The research team plan to develop an improved theory for tornadogenesis and demonstrate a direct link between the ambient wind profile and the rotation of a tornado. The research pursues two objectives. The first is related to the intensification of the vortex during the transition of the near-ground vorticity dynamics recently discovered by the research team’s group, while the second explores the possibility of ambient vorticity being utilized directly by the tornado. The project will be modelling-based, using the CM1 numerical model at 50m resolution for tornado simulations and 100m resolution for supercell simulations. Six hypotheses would be addressed, 4 related to tornado intensification and 2 regarding the environmental source of vorticity:• The transition toward the in-and-up mechanism results in rapid intensification of the vortex.• This transition is accompanied by a feedback loop at the scale of the vortex.• Whether or not the transition occurs depends on the strength of the initial vortex patch.• Once the in-and-up mechanism is active, the influx of vertical vorticity is no longer required (but not harmful) for vortex maintenance. However, continued influx of vertical vorticity may influence the diameter and intensity of the vortex.• In cases where there is large ambient storm-relative streamwise vorticity at the origin height of the relevant parcels, the barotropic vorticity reinforces, or sometimes dominates, the horizontal near-ground vorticity that has been produced via surface drag and baroclinicity. • In cases where there is ambient storm-relative crosswise vorticity at the origin height of the relevant parcels, the barotropic vorticity weakens the horizontal near-ground vorticity that has been produced via surface drag and baroclinicity.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.