1.北京城市气象研究院，北京 100089;2.中国科学院大气物理研究所云降水物理与强风暴实验室，北京 100029;3.广西壮族自治区气象台，南宁 530022
1.Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089;2.Key Laboratory of Cloud-Precipitation Physics and Severe Storms (LACS), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029;3.Guangxi Meteorological Observatory, Nanning 530022
本文利用雷达、加密地面自动站等高时空分辨率的观测资料，结合NCEP 1°×1°再分析资料、常规观测等资料，对2011年6月23日发生在北京城区的极端强降水事件开展了细致的观测和诊断分析。结果表明，这次极端强降水事件，主要是由向东南移动的东北—西南走向的飑线右端的强降水超级单体（High Precipitation Supercell，简称HPS）造成的，这是目前已有文献记载的中国发生纬度最高的HPS。HPS在移动方向的右后侧和右前侧均有明显的“V”型入流，这不同于已有HPS模型，表明中、低层干冷空气和低层暖湿气流特征显著。在环境条件方面，存在对流层低层逆温层，其能量存储盖作用使得雷暴具有爆发性增强的潜势，但该逆温层是在08:00～14:00（北京时，下同）的6小时内形成的，对业务预报极具挑战性。相对其他大气层结热动力参数， 风暴相对螺旋度和粗理查逊数在14:00较08:00显著增大，对HPS的发生具有一定指示作用。高空偏西风急流和低层偏东风活动显著，使得北京地区的水平风垂直切变增强，形成上干下湿的对流不稳定以及次级环流圈。高空急流造成强烈的相当位温差动平流，促进对流不稳定度发展加强。结合复杂地形作用，在北京西部100 m地形高度线附近形成显著的平原暖湿空气与山地干冷空气的干湿分界线以及风场辐合线。水汽供应主要源自低层偏东风和本地水汽积累。当飑线从西北方向侵入北京并向东南方向移动时，在北部山区，由于条件不足，雷暴没有显著发展加强；然而，在西部山区，在湖面、城市热岛、低层偏东风、冷池出流共同作用下，加之其他有利的环境条件，飑线右端雷暴强烈发展加强，特别是当经过100 m地形高度线附近时发展成为HPS，进而造成石景山区模式口站的大暴雨中心。
In this paper, an observational and diagnostic analysis of an extreme heavy precipitation (EHP) event in Beijing on 23 June, 2011 is performed. This analysis used radar-observed data and automated weather station observations with high time and space resolution, combined with NCEP 1°×1° reanalysis data and conventionally observed data. Results showed that the EHP event was attributable to the high precipitation supercell (HPS) at the right end of the squall line moving southeast, which occurred at the highest latitude recorded among all HPS events documented in China thus far. The HPS had distinctive V-shaped inflows in both in the right-front and right-rear flanks, which differed from those in the known HPS model. This indicated that the cold dry air flow at mid- and lower levels and the warm moist air flow at lower levels were significant. In terms of environmental conditions, there was an inversion layer (IL) in the lower levels of the troposphere, indicating that the thunderstorm would intensify explosively when the cap was broken. However, the IL formed within 6 hours from 0800 BT (Beijing time) to 1400 BT, which was difficult to forecast. Compared with other thermodynamic parameters, storm-relative helicity and bulk Richardson number sharply increased from 0800 BT to 1400 BT before the occurrence of the HPS, which had certain indicative effects. The westerly upper-level jet and low-level easterly wind were significant, which enhanced the vertical shear of horizontal wind over Beijing, facilitated the convective instability with the dry upper layer and moist lower layer, and formed the secondary circulation. Meanwhile, the upper-level jet caused obvious differential vertical advection of equivalent potential temperature, which maintained and strengthened the convective instability. Combined with the terrestrial effects, there existed both an obvious dry-moist boundary line and a wind convergence line near the 100 m topographic elevation line in western Beijing. The water vapor supply was mainly from the low-level easterly wind and local water vapor. When the squall line invaded Beijing from the northwest and moved to the southeast, in the northern mountainous areas, the thunderstorm did not develop significantly due to insufficient conditions. In contrast, in the western mountainous areas, supported by a lake, the urban heat island effect, low-level easterly winds, a cold pool outflow, and the other favorable environmental factors, the thunderstorm at the right end of the squall line strengthened significantly. Notably, it developed into the HPS when it reached the 100 m topographic elevation line, which, in turn, caused the rainstorm center at the Moshikou station of Shijingshan District.