Mesoscale Studies of Convection, Tornadogenesis and Fronts

首席研究员将在以下领域进行研究：1)龙卷风和龙卷风形成；2)弓形回波结构；3)暖锋的中尺度记录；4)参与国际水蒸汽项目（IHOP）的实地阶段。前三个领域的研究是基于对过去实地试验收集的现有数据的彻底分析。基于在VORTEX（验证龙卷风旋转起源实验）期间收集的数据的两个案例研究正在进行审查。为了调查先前研究结果的普遍性，将对德克萨斯州斯威特沃特附近形成的与超级单体有关的一场有充分记录的龙卷风进行研究。“甜水”风暴还催生了几个没有形成龙卷风的低层中气旋。因此，利用可比较的空间和时间分辨率数据，有一个独特的机会来比较与同一个超级单体相关的龙卷风和非龙卷风低层中气旋。第二个案例研究是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信号，通常与下爆和回波有关。本案例提供了一个机会来检查这种回声从线性结构到弓形的演变。1997年冬季，为研究海洋气旋的形成，进行了一项国际野外试验，称为FASTEX（锋和大西洋风暴路径试验）。主要数据平台是几架研究飞机，这些飞机释放了落风探空仪，记录了飞行水平的原位测量数据，并使用机载雷达收集了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很大程度上占据了文献的主导地位，因为它的结构明确，通常表现为风的突变和温度的不连续性，并且它经常与强对流天气有关。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暖锋通常与强烈的不连续面没有联系，尤其是在大陆上空。在fastx期间，在暖锋上收集了一组独特的数据。利用多普勒风合成和dropwindsonde信息收集了锋面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流在地转平衡中的程度和锋生方程的条款。IHOP （International H20 Project）的主要目标是改进对水汽四维分布的测量，更好地了解水汽对降水预报的影响。实地试验阶段计划于2002年春季进行。在这个项目中，PI将解决一些研究目标，这些目标涉及IHOP的对流启动组件。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)确定沿辐合边界发展的弯变/环流的产生机制及其对水汽场演变的影响；3)定量评价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的平衡对确定对流起生势的重要性。

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.