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）暖锋的中尺度文件，以及4）参与国际水汽项目（IHOP）的现场阶段。 对前三个领域的研究是基于对过去实地实验收集的现有数据的全面分析，目前正在审查两个基于涡动实验（验证龙卷风旋转起源实验）收集的数据的案例研究。 一个有据可查的龙卷风与得克萨斯州斯威特沃特附近发展的超级单体相关，将进行研究，以调查以前的研究结果的一般性。 甜水风暴还催生了几个没有产生龙卷风的低层中气旋。 因此，有一个独特的机会，比较龙卷风和非龙卷风低层中气旋与同一超级单体使用的数据可比的空间和时间分辨率。 第二个案例研究是基于机载多普勒数据收集的弓形回波，在一个飑线内发展。 弓形回波是一种常见的雷达特征，通常与下击暴流和derecho相关。 1997年冬季，国际上组织了一个名为FASTEX（锋面和大西洋风暴路径实验）的海洋气旋生成实验，对海洋气旋生成过程进行了研究。 主要的数据平台是几架研究飞机，这些飞机投放下投式风测仪，记录飞行高度的现场测量结果，并利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主导地位，主要是因为它具有明确的结构，通常表现为突然的风移和温度不连续性，以及它与强对流天气的频繁联系。 相比之下，对地面暖锋的观测研究相对较少。 这在一定程度上是由于暖锋通常不与强间断相关联，特别是在大陆上。 一个独特的数据集收集在一个暖锋在FASTEX。 利用多普勒风合成和下投式探空仪资料收集了锋区详细的运动学和热力学数据。 这项研究的具体目标包括检查在何种程度上的流量是在地转平衡和锋生equation.The IHOP（国际H20项目）的主要目标是改善测量的四维分布的水汽和更好地了解水汽对降水预报的影响。 计划于2002年春季进行实地试验。 在这个项目中，PI将解决一些与IHOP的对流启动组件处理的研究目标。 这些目标包括：1）全面记录水平对流卷对对流边界层内湿度变化的影响; 2）确定沿沿着辐合边界发展的弯折/环流的产生机制及其对演变中的湿度场的影响;和3）对雷暴外流冷池产生的水平涡度与由低层切变矢量产生的环境涡度决定对流开始的可能性。