Analysis of Instability Mechanism of an Extreme Blizzard Accompanied by Elevated Thunderstorms
Based on conventional observation,three-dimensional lightning locator,Doppler weather radar and ERA5 reanalysis data,the characteristics of a convective event on 14 December 2023 in Shandong Province are analyzed.The position of the ground cold front is determined by using the frontogenesis func-tion,the dense zone of pseudo-equivalent temperature,and the temperature variation.A conceptual model diagram of the physical process is proposed.The results show that thunderstorm and heavy snowfall oc-curred at the rear of the ground cold front,with a deep and stable cold cushion in the low altitude,and strong warm and humid air above the temperature inversion layer,forming the environment for elevated thunderstorm.During the blizzard,there was convective-symmetric instability,and the symmetric insta-bility and potential instability were at different levels.The symmetric instability was below 700 hPa,and the tilting convection developed during the forced uplift of warm and humid air flow along the low-level cold cushion.The potential instability was located at 700-500 hPa and was established with the advancement of the southwest jet.When the tilting convection caused by symmetric instability reached a level of 700-500 hPa,the energy of potential instability was released,leading to the development of deep and strong vertical convection.The establishment of potential instability was consistent with the northward advance of 20 m·s-1wind speed at 700-500 hPa,which was 1-2 h ahead of the heaviest snowfall and thunder.The triggering of elevated thunderstorm was not only related to the uplift of the low-level cold cushion,but also to the enhancement of wind near 700-500 hPa in the middle layer.With the increase of wind speed at 700-500 hPa,the positive vorticity advection was strengthened,and then the upward airflow fur-ther developed,causing severe snowfall and high-frequency lightning.The convective property of this ele-vated convection was not typical and the echo intensity was mainly concentrated in 20-35 dBz,but the echo top height exceeded the-30℃ layer height and the 35 dBz echo extended above the-10℃ layer height.Therefore,it is still necessary to pay close attention to the occurrence of lightning in winter.
万方数据
维普
