A Doppler Radar Climatology of Updraft Proxy Characteristics in Supercells

该项目涉及使用气象雷达信号来估计一个重要的风暴特征的大小和倾斜，即风暴上升气流，在严重的雷暴中。上升气流是快速上升的空气被输送到高空形成云并最终降水的区域。上升气流对风暴产生的每一种危害都有贡献，尤其是大冰雹和龙卷风。过去的研究提供了证据，表明与上升气流较小的风暴相比，较大的风暴上升气流会产生更强的龙卷风和更大的冰雹。此外，研究表明，垂直垂直的风暴上升气流，而不是倾斜的，也更有可能产生龙卷风。不幸的是，很难直接观测和测量风暴上升气流的特征。然而，对美国雷达网络进行的升级已经引入了新的选项来跟踪作为上升气流代理的特征。在这个项目中，研究人员使用雷达特征的大小和倾斜度来估计100多个实际风暴案例中上升气流的相同特征，以更好地确定上升气流大小和倾斜度与龙卷风和冰雹的发生有多密切相关。研究人员还将确定形成风暴的天气条件是否与上升气流的大小和倾斜程度有关。该项目的最终目标是为预报员提供新的工具，帮助他们提醒公众注意即将产生强烈龙卷风和/或超大冰雹的风暴。正在研究的风暴类型是超级单体雷暴，它通常会产生最强的龙卷风和最大的冰雹。为了估计超级单体上升气流的大小和倾斜程度，研究人员使用了一种新的算法，该算法可以自动检测双极雷达特征，即ZDR柱，当上升气流将雨水和小冰雹提升到冰点以上时形成。这些数据将与传统的雷达分析结合使用，以确定上升气流代理特征、近风暴环境和大量超级单体案例中危害产生之间的联系。具体而言，该项目旨在(i)确定中层上升气流区域、低层上升气流区域与龙卷风和大冰雹发生之间的紧密联系，（ii）量化上升气流垂直对齐对龙卷风产生的必要程度，（iii）近风暴环境控制（如果存在的话），上升气流大小和对齐，以及（iv）将(i)和（ii）的结果与另一个双极雷达特征数据（ZDR-KDP分离矢量）结合起来。优化已知的龙卷风形成及高峰龙卷风强度预测指标，以供实际应用。此外，根据项目结果，将探讨准确评估这些特征的能力及其在危险天气临近预报中的潜在用途。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The project concerns the use of weather radar signatures to estimate the size and tilt of an important storm feature, the storm updraft, within severe thunderstorms. The updraft is an area of rapidly rising air that is transported aloft to form clouds and eventually precipitation. The updraft contributes to every hazard that a storm produces, notably large hail and tornadoes. Past work has provided evidence that larger storm updrafts produce stronger tornadoes and larger hail compared to storms with smaller updrafts. In addition, studies have hinted that storm updrafts that are vertically upright, as opposed to tilted, are also more likely to produce tornadoes. Unfortunately, it is difficult to directly observe and measure characteristics of the storm updraft. However, upgrades performed to the U.S. radar network have introduced new options to track features that serve as a proxy for the updraft. In this project, the researchers use the size and tilt of this radar feature as an estimate for those same characteristics in the updraft in more than 100 actual storm cases to better determine how closely linked updraft size and tilt are to tornado and hail occurrence. The researchers also will determine if the weather conditions feeding into the storm are linked to the size and tilt of the updraft. The project objectives ultimately aim to provide forecasters with new tools that may help them alert the public to storms that are about to produce strong tornadoes and/or very large hail.The storm type being studied is the supercell thunderstorm, which generally produces the strongest tornadoes and largest hail. To estimate the size and tilt of supercell updrafts, the researchers use a novel algorithm that automates detection and area of a dual-pol radar signature, the ZDR column, which forms when an updraft lofts rain and small hail above the freezing level. Those data will be used in tandem with traditional radar analyses to identify links between updraft proxy characteristics, the near-storm environment, and hazard production in large numbers of supercell cases. Specifically, this project seeks to (i) determine a firm link between midlevel updraft area, low-level updraft area, and tornado and large hail occurrence, (ii) quantify the degree to which updraft vertical alignment is necessary for tornado production, (iii) the near-storm environmental controls, if they exist, on both updraft size and alignment, and (iv) combine the results from (i) and (ii) with data of another dual-pol radar signature, the ZDR-KDP separation vector, to optimize known predictors of tornado formation and peak tornado intensity for possible operational use. In addition, depending on project results, the ability to accurately assess these characteristics and their potential use in nowcasting of hazardous weather will be explored.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.