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华北初春一次高架雷暴天气的环境条件及抬升触发机制分析

Analysis of Environmental Conditions and Lifting Trigger Mechanism of an Elevated Thunderstorm in Early Spring in North China

  • 摘要: 2018年4月4日,华北发生一次暴雪伴随高架雷暴的天气过程,利用国家站、区域站观测和ERA5再分析资料,采用天气诊断和绝对地转动量距平调整等方法探讨了此次天气过程的环境条件和雷暴触发机制。研究发现:(1)此次天气过程发生在冷锋过境后的北侧冷区内,是一次在华北冷季回流形势下伴随暴雪发生的高架雷暴过程。(2)该过程有利的环境背景条件有:东路冷空气遇太行山阻挡后形成干冷垫,导致强逆温层的出现,减弱了拖曳作用,从而有利于对流活动的发展。同时,对流层中层的水汽水平输送为高架雷暴提供了必要的水汽和能量支持。(3)湿位涡分析表明,高架雷暴发生在逆温层上方对流稳定但对称不稳定的区域内,有利于倾斜上升气流发展。(4)地面辐合线、地形等因素引起初始上升运动,尽管中性层结抑制上升运动,但上升气流在绝对地转动量距平调整(△M调整)下进入对称不稳定区域,释放能量,激发持续的倾斜上升气流,扩展到200 hPa高度,形成初春高架雷暴。

     

    Abstract: On 4 April 2018, a snowstorm accompanied by elevated thunderstorms occurred in North China. Using observations data from national and regional stations, as well as ERA5 reanalysis data, weather diagnosis and absolute momentum anomaly adjustment methods were employed to investigate the environmental conditions and thunderstorm triggering mechanisms of this weather event. The study found that: (1) This weather event occurred within the cold sector to the north of a passing cold front, representing an elevated thunderstorm event accompanied by a snowstorm under the influence of a return flow pattern during the cold season in North China. (2) Favorable environmental conditions for this event included the formation of a dry and cold air mass after eastern-route cold air encountered the blockage of the Taihang Mountains, leading to the emergence of a strong inversion layer that weakened the drag effect and thereby favored the development of convective activities. Meanwhile, horizontal water vapor transport in the middle troposphere provided necessary water vapor and energy support for the elevated thunderstorm. (3) Wet potential vorticity analysis indicated that the elevated thunderstorm occurred within a region of convective stability but symmetrical instability above the inversion layer, which was conducive to the development of tilted upward air currents. (4) Factors such as surface convergence lines and terrain induced initial upward motion. Although the neutral stratification suppressed upward motion, the upward air currents entered the region of symmetrical instability under the adjustment of absolute momentum anomalies (ΔM adjustment), releasing energy and triggering sustained tilted upward air currents that extended to an altitude of 200 hPa, forming an elevated thunderstorm in early spring.

     

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