雅安市一次层结对流稳定条件下暴雨的特征及分析

The Characteristics and Analysis of a Rainstorm under the Stable Atmospheric Stratification in Ya’an

文章针对雅安地区在层结对流稳定条件下发生的一次暴雨事件开展了系统分析。研究结果表明,此类暴雨具有小时雨强较小、降水持续时间长、影响范围广泛、南北差异显著等特点,其降雨范围和强度均小于强对流型暴雨。此次暴雨发生于弱冷空气影响下的层结稳定天气背景中,受青藏高原东坡地形抬升作用影响,雅安中部形成了低涡。然而,该低涡发展较为有限,上升运动高度偏低。雷达回波数据进一步证实,此次降水主要由层云降水构成,回波发展高度较低。弱冷空气南下过程促进了大气不稳定层结的建立和不稳定能量的释放,有利于降水强度的增强。在此次降水过程中,中低层偏南风持续输送充沛水汽,为降水的长时间维持提供了有利条件。This paper systematically analyzes a rainstorm event under stable atmospheric stratification. The research results show that this kind of rainstorm has the characteristics of small hourly rainfall intensity, long rainfall time, wide rainfall range, and obvious differences between the north in Ya’an and the south. The range and magnitude of this rainstorm are smaller than that of a strong convection rainstorm. The weather background of this rainstorm is weak cold air, stable stratification. Due to the uplift effect of the terrain on the eastern slope of the plateau, a vortex is formed in the center of Ya’an. However, the development of this vortex is relatively limited, and the height of the ascending motion is also relatively low. The radar echo further confirms that this precipitation is mainly composed of stratiform cloud precipitation, and the development height of radar echo is relatively low. The southward movement of weak cold air promotes the establishment of unstable stratification and the release of unstable energy, which is beneficial for enhancing precipitation intensity. During this precipitation process, the southerly wind in the middle and low levels brought abundant water vapor, which made the precipitation maintain for a long time.