Mesoscale Studies of Convection, Tornadogenesis and Fronts

对流、龙卷发生和锋面的中尺度研究

• 批准号: 0121048
• 负责人: Robert Fovell
• 金额: --
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-03-01 至 2008-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0121048&HistoricalAwards=false
• 关键词: Mesoscale; Studies; Convection; Tornadogenesis; Fronts

The Principal Investigator will perform research in the areas of: 1) tornadoes and tornadogenesis, 2) structure of bow echoes, 3) mesoscale documentation of warm fronts, and 4) participation in the field phase of the international water vapor project (IHOP). The research on the first three areas is based upon a thorough analysis of existing data collected from past field experiments.Two case studies based on data collected during VORTEX (Verification on the Origins of Rotation in Tornadoes Experiment) are being examined. A well-documented tornado associated with a supercell that developed near Sweetwater, Texas will be studied in order to investigate the generality of prior research results. The Sweetwater storm also spawned several low-level mesocyclones that did not produce tornadoes. Accordingly, there is a unique opportunity to compare tornadic and non-tornadic low-level mesocyclones associated with the same supercell using data of comparable spatial and temporal resolution. A second case study is based on airborne Doppler data collected on a bow echo that developed within a squall line. The bow echo is a common radar signature that is often associated with downbursts and derechos. The present case provides an opportunity to examine the evolution of this echo from a linear structure into a bow-shape.During the winter of 1997, an international field experiment called FASTEX (Fronts and Atlantic Storm Track Experiment) was organized to study oceanic cyclogenesis. The primary data platforms were several research aircraft which released dropwindsondes, recorded in situ measurements at flight level, and collected high-resolution radar reflectivity and Doppler velocity information using on-board radars. Observational and numerical studies on cold fronts have dominated the literature largely because of its well-defined structure, often manifested as abrupt wind shifts and temperature discontinuities, and its frequent association with severe convective weather. In comparison, there have been relatively few observational studies of surface warm fronts. This is due, in part, to the fact that warm fronts are often not associated with strong discontinuities especially over the continents. A unique data set was collected on a warm front during FASTEX. Detailed kinematic and thermodynamic data were collected on the frontal zone using Doppler wind syntheses and dropwindsonde information. Specific goals of this research include examining the degree to which the flow was in geostrophic balance and the terms of the frontogenesis equation.The primary goal of IHOP (International H20 Project) is to improve measurements of the four-dimensional distribution of water vapor and better understand the impact of water vapor on precipitation forecasting. The field phase of the experiment is planned for Spring 2002. In this project the PI will address a number of research objectives that deal with the convection initiation component of IHOP. These objectives include: 1) a thorough documentation of the impact of horizontal convective rolls on moisture variations within the convective boundary layer; 2) determining the generating mechanism(s) of inflections/circulations that develop along convergence boundaries and their impact on the evolving moisture fields; and 3) a quantitative assessment of the importance of the balance between the horizontal vorticity generated by the cold pool from thunderstorm outflows with the environmental vorticity produced by the low-level shear vector in determining the potential for convection initiation.

首席研究员将在以下领域进行研究：1）龙卷风和龙卷风发生，2）弓形回波结构，3）暖锋的中尺度记录，4）参与国际水汽项目（IHOP）的现场阶段。 前三个领域的研究基于对过去现场实验收集的现有数据的彻底分析。正在审查基于 VORTEX（龙卷风旋转起源实验验证）期间收集的数据的两个案例研究。 我们将对德克萨斯州斯威特沃特附近形成的与超级单体相关的有据可查的龙卷风进行研究，以调查先前研究结果的普遍性。 甜水风暴还催生了几个低级中气旋，但并未产生龙卷风。 因此，有一个独特的机会可以使用具有可比空间和时间分辨率的数据来比较与同一超级单体相关的龙卷风和非龙卷风低级中气旋。 第二个案例研究基于在飑线内形成的弓形回波收集的机载多普勒数据。 弓形回波是一种常见的雷达特征，通常与下击暴流和反回波相关。 本案例提供了一个机会来研究这种回波从线性结构到弓形的演变。 1997 年冬天，组织了一项名为 FASTEX（锋面和大西洋风暴轨迹实验）的国际现场实验来研究海洋气旋发生。 主要数据平台是几架研究飞机，它们释放落风探空仪，记录飞行高度的现场测量结果，并使用机载雷达收集高分辨率雷达反射率和多普勒速度信息。 对冷锋的观测和数值研究在文献中占据主导地位，主要是因为其结构明确，通常表现为突然的风向变化和温度不连续性，并且经常与强对流天气相关。 相比之下，对地表暖锋的观测研究相对较少。 部分原因是暖锋通常与强烈的不连续性无关，尤其是在大陆上。 FASTEX 期间在暖锋上收集了一组独特的数据。 使用多普勒风合成和落风探空仪信息收集了锋区的详细运动学和热力学数据。 这项研究的具体目标包括检查水流处于地转平衡的程度以及锋生方程的项。IHOP（国际 H20 项目）的主要目标是改进对水蒸气四维分布的测量，并更好地测量水蒸气的分布。了解水蒸气对降水预报的影响。 实验的现场阶段计划于 2002 年春季进行。在这个项目中，PI 将实现一些涉及 IHOP 对流引发部分的研究目标。 这些目标包括： 1) 全面记录水平对流卷轴对对流边界层内湿度变化的影响； 2) 确定沿收敛边界发展的拐点/环流的生成机制及其对不断变化的湿度场的影响； 3) 定量评估雷暴流出冷池产生的水平涡度与低层切变矢量产生的环境涡度之间平衡的重要性，以确定对流引发的可能性。