中国东部高架雷暴环境特征及其形成演变机制研究

Elevated thunderstorm accounts for a certain proportion of the thunderstorms, which can create disastrous severe convective weathers like hail, short-time severe precipitation etc.. Due to the lack of recognizing its formation mechanism, elevated thunderstorm is very difficult to be predicted accurately. To improve the forecasting capability to elevated thunderstorms and severe convective weathers, in this project we will collect and build datasets for the elevated thunderstorms in the past 10 years over the eastern part of China, count up and analyze the dynamic and thermodynamic environmental parameters of elevated thunderstorms and the distribution characteristics of the induced severe convective weather. Besides, we will analyze the ambient field of typical elevated thunderstorms by using the pattern identification method and the severe weather analysis method which is based on the constituent elements, and work out a conceptual model for the formation and development of elevated thunderstorms in different areas of eastern China by combining gestrophic, quasi-geostrophic or frontogenesis theory; analyze the different effects of different unstable mechanisms on the formation of elevated thunderstorms and study the unstable mechanism of the dominant elevated thunderstorm under different flow patterns; utilize high-resolution mesoscale numerical model to simulate typical elevated thunderstorm cases and do the sensitivity tests, investigating the impacts of low-level stable boundary layer and low-level jet stream on the development and maintenance of elevated thunderstorms and on the severe convective weathers. The research results of this project will be beneficial to recognizing the formation and development mechanisms of elevated thunderstorms in the east of China, thus provide references for improving the forecasting accuracy of elevated thunderstorms and severe convective weathers in China.

高架雷暴在雷暴中占有一定比例，能引发冰雹、短时强降水等灾害性强对流天气。由于对其形成机制缺乏认识，目前仍是业务预报工作中的难点。本项目拟收集近10年我国东部地区高架雷暴数据并建立数据集，统计分析高架雷暴的动力学和热力学环境参量及其引发的强对流天气分布特征；利用流型识别法和基于构成要素的强天气分析法分析典型高架雷暴的环境背景场，结合地转、半地转或锋生理论给出东部地区不同区域高架雷暴形成发展的概念模型；分析不同不稳定机制对高架雷暴形成的作用，研究不同流型下主导高架雷暴的不稳定机制；利用高分辨率中尺度数值模式对典型个例进行数值模拟和敏感性试验，研究低层稳定层、低空急流等对高架雷暴发展和维持的影响及对强对流天气的影响。项目研究结果将有助于系统认识我国东部地区高架雷暴的形成机理，并为提高我国高架雷暴及强对流天气业务预报准确率提供参考依据。

高架雷暴在雷暴中占有一定比例，能引发冰雹、短时强降水等灾害性强对流天气，由于其发生在冷的边界层下而容易漏报，冷特别是冷季高架。项目在回顾国内外高架对流研究成果的基础上建议给出了中国高架对流判据，并基于此判据筛选了近10年中国东部高架雷暴个例，统计得到了高架雷暴的时空分布特征、环境要素特征和不稳定机制及其引发的强对流天气特征。对典型的冷锋后高架冰雹和暴雪、暖锋前高架冰雹、盛夏冷锋后高架暴雨个例进行了深入分析，表明中国东部主要为冷锋后高架对流，长江以南的高架对流的不稳定机制为弱的条件不稳定，大多情况下为位势不稳定层结在锋面抬升作用下转化为弱的条件不稳定，高架对流发生时其CAPE值多在500J/kg以下；条件对称不稳定和弱条件稳定度或近湿中性大气层结下的锋生强迫引发的较强上升运动是造成华北冷季高架对流的主要不稳定机制。冷锋后由条件不稳定导致的高架对流主要表现为层云内镶嵌积云造成强降水和小冰雹，由条件对称不稳定导致的高架对流产生带状回波造成强降雪或降水；暖锋前高架对流表现为强烈的超级单体雹暴。850-700hPa低空强暖湿平流和锋面抬升是高架雷暴形成的关键系统，高架对流发生时冷高压强且中心多偏东，强冷空气或补充冷空气强迫其南侧暖湿气流抬升形成高架对流的情形在北方比较多见，而黄河以南地区则表现为暖湿气流在前期冷空气形成的冷垫上爬升。理论推导和实例分析均表明，二维相当位涡和湿对称不稳定斜率判据是一致的，但不能扩展至三维，从不稳定能量角度对条件不稳定进行了讨论，对全型涡度方程及其倾斜涡度项进行了讨论。