Concentrating Vorticity Near the Ground: An Investigation of the Interaction of Precipitation Processes and Flow Dynamics in Supercells and Other Severe Thunderstorms

近地集中涡度：超级单体和其他强雷暴中降水过程与流动动力学相互作用的研究

• 批准号: 0003869
• 负责人: Erik Rasmussen
• 金额: $ 47.33万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-01-01 至 2004-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003869&HistoricalAwards=false
• 关键词: Concentrating; Vorticity; Near; Ground; Investigation

During the Springs of 1994 and '95, a field program entitled the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) was executed by a combination of NSF and National Oceanic and Atmospheric Administrations sponsored scientists. The primary objective of VORTEX was to evaluate several hypotheses pertaining to low-level mesocyclone intensification, and tornado formation, maintenance, and demise. The observations collected included ground-based (mobile and stationary) and airborne Doppler radars, mobile surface and balloon borne meteorological instruments. Under this award, the Principal Investigators will continue their ongoing research intended to advance state of knowledge of the life cycles of tornadoes. This goal will be accomplished through careful examination of data-rich case studies of the Dimmitt, Friona, and Wheeler (all in Texas) tornadic storms as well as other storms (some tornadic, some not) from the VORTEX and subsequent experiments. As a result of prior research, it has become apparent that future investigations must be expanded to cover a variety of closely related processes to understand tornadogenesis and tornado longevity. Among these are:-factors that govern the amount and type of precipitation that forms/descends in rear flank downdrafts (RFD) at the rear of supercell updrafts;-how this precipitation and its type is related to formation of RFDs;-how RFD generate vorticity and/or barotropically redistribute it:-how outflow from the RFD can be confined to the region below the updraft;-how RFDs lead to the formation of tornado cyclones, and whether the angular momentum of the tornado cyclone is maintained by the RFD or merely "spins down" from some initial distribution;-whether the RFD can lead directly to a tornado cyclone through largely barotropic processes;-whether the tornado cyclone forms from upward tilting of helicity-rich inflow air;-whether only one or both of the above processes is required for tornadogenesis;-whether the depth, size and shape of RFDs are relevant to tornadogenesis.Most of these questions can be, or have been, cast in the form of testable, refutable hypotheses. The Principal Investigators will emphasize the development of theories and models for RFD vorticity processes and the effect of precipitation in redistributing angular momentum in a mesocyclone-scale vortex. The Principal Investigators also will investigate the role of hydrometeors and water phase changes in forcing the kinematic structures.Successful completion of this research could lead to a reduction in tornado warning false alarm rate while maintaining adequate lead times.

在1994年和1995年的春天，由NSF和国家海洋和大气管理局赞助的科学家联合执行了一项名为“验证龙卷风实验中旋转起源”的实地方案。 涡的主要目的是评估有关低层中气旋增强，龙卷风的形成，维持和消亡的几个假设。 收集的观测资料包括地面（移动的和固定的）和机载多普勒雷达、移动的地面和气球携带的气象仪器。根据该奖项，主要研究人员将继续他们正在进行的研究，旨在推进龙卷风生命周期的知识状态。 这一目标将通过仔细检查数据丰富的案例研究来实现，这些案例研究包括迪米特、弗里奥娜和惠勒（都在德克萨斯州）龙卷风风暴以及来自涡和后续实验的其他风暴（有些是龙卷风，有些不是）。作为先前研究的结果，很明显，未来的研究必须扩大到涵盖各种密切相关的过程，以了解龙卷风的形成和龙卷风的寿命。 这些因素包括：-决定后方形成/下降的降水量和类型的因素 超级单体上升气流后部的下降气流（RFD）;-这种降水及其类型如何与RFD的形成相关;-RFD如何产生涡度和/或正压重新分配它：-如何将RFD的流出限制在上升气流下方的区域;-RFD如何导致龙卷风的形成，以及龙卷风的角动量是否 龙卷风气旋是由RFD维持的，或者仅仅是从一些初始的 分配;- RFD是否可以通过主要的正压过程直接导致龙卷风气旋;-龙卷风气旋是否是由富含螺旋度的流入空气向上倾斜形成的;-龙卷风的形成是否只需要上述过程中的一个或两个;-RFD的深度、大小和形状是否与龙卷风发生相关。这些问题中的大多数可以或已经以可检验、可反驳的假设的形式出现。 主要研究人员将着重于RFD涡度过程的理论和模型的发展，以及降水在中气旋尺度涡中重新分配角动量的作用。 主要研究人员还将调查水凝物和水相变化在迫使运动学结构中的作用。这项研究的成功完成可能会导致龙卷风警报误报率的降低，同时保持足够的提前时间。