Mesoscale Studies of Convection, Tornadogenesis and Fronts

首席调查员将在以下领域开展研究：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，以及4)参与国际水汽项目(IHOP)的实地阶段。对前三个领域的研究是在对过去现场实验收集的现有数据进行透彻分析的基础上进行的。目前正在审查两个案例研究，这些研究基于在涡旋期间收集的数据(关于龙卷风旋转起源的验证)。为了调查先前研究结果的一般性，将对德克萨斯州斯威特沃特附近发展起来的与超级单体有关的龙卷风进行研究。甜水风暴还催生了几个没有产生龙卷风的低级别中气旋。因此，有一个独特的机会来比较与同一超级单体有关的龙卷风和非龙卷风低层中气旋，使用可比较的空间和时间分辨率的数据。第二个案例研究是基于空中多普勒数据收集的弓形回波，这种回波是在一条狂风线内发展起来的。弓形回波是一种常见的雷达信号，通常与下击暴流和反回波联系在一起。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化。1997年冬天，组织了一项名为FASTEX(锋面和大西洋风暴路径实验)的国际野外实验，以研究海洋气旋发生。主要的数据平台是几架研究飞机，这些飞机释放下落探测仪，记录飞行水平的现场测量，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。冷锋的观测和数值研究在很大程度上占据了文献的主导地位，这主要是因为它的结构很明确，通常表现为突然的风向变化和温度间断，而且它经常与强对流天气联系在一起。相比之下，对地表暖锋的观测研究相对较少。这在一定程度上是由于这样一个事实，即暖锋通常与强烈的不连续联系在一起，特别是在大陆上。在FASTEX期间，在暖锋上收集了一个独特的数据集。利用多普勒风合成和落风探测仪信息收集了额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验气流处于地转平衡的程度和锋生方程的项。IHOP(国际H20项目)的主要目标是改进对水汽四维分布的测量，并更好地了解水汽对降水预报的影响。试验的实地阶段计划在2002年春季进行。在这个项目中，PI将涉及与IHOP对流启动部分有关的一些研究目标。这些目标包括：1)详细记录水平对流卷对对流边界层内水分变化的影响；2)确定沿辐合边界发展的弯曲/环流的产生机制(S)及其对水汽演变场的影响；3)定量评估雷暴外流产生的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的平衡在确定对流引发潜力方面的重要性。

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.