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一次暴雪过程的高架雷暴环境条件及雷达特征

Synoptic conditions and radar characteristics for elevated thunderstorm during a snowstorm event in Henan Province

  • 摘要: 2021年2月24—25日河南出现一次伴高架雷暴的暴雪天气过程,各级气象台站业务预报对该过程中雷暴均漏报,对降雪量级预报也偏小。利用常规气象观测资料、双偏振雷达产品和NCEP 1°×1°逐6 h再分析资料,重点分析了这次暴雪过程中高架雷暴的环境条件及双偏振雷达参量特征。结果表明: (1)东移加深的中纬度高空槽、700 hP a发展北上的西南急流与地面扩散南下的冷空气等天气尺度系统相互作用触发对流,造成暴雪过程出现高架雷暴。(2)该过程最强水汽输送位于700 hPa,水汽通量大值带位于河南沿黄(河)一带,河南上空水汽充足,为中层不稳定层结建立和对流触发提供了有利的热力条件。(3)低槽前部两个次级环流圈上升支叠加为雷暴发生和降雪增强维持提供了强的上升运动;0—6 km较强垂直风切变有利于对称不稳定发展;700 hPa西南风急流辐合作用配合高空槽大尺度强迫使得中高层不稳定能量释放,从而触发对流。(4)高架雷暴发生时,雷达回波强度≥45 dBz、顶高超过-20℃层,“牛眼”结构和辐合上升区长时间维持有利于产生雷暴;雷达双偏振参量相关系数(CC)较小(0.7~0.9)、差分相移率(KDP)较大(0.5°~0.7°·km-1)和差分反射率(ZDR)>2 dB是高架雷暴发生时的主要特征,回波强度>55 dBz并伴有较大KDP (0.5°~0.7°·km-1)与雷电频发和强降雪时段相对应。

     

    Abstract: A snowstorm event followed by the elevated thunderstorm occurred in Henan Province from February 24 to 25 in 2021. The operational forecast of all meteorological stations failed to capture the thunderstorm of this event, with the snowfall being underestimated. Using the conventional meteorological observations, the dual polarization weather radar products, and the NCEP/NCAR reanalysis with special resolution of 1° and temporal resolution of 6 h, we conducted the analysis of the synoptic conditions and the characteristics of the dual polarization radar parameters for the elevated thunderstorm during this event. Results are as follows. (1) Due to the interaction of synoptic scale systems such as the mid-latitude upper trough moving eastward and deepening, the southwest jet developing northward at 700 hPa, and the cold air diffusing southward from the surface, the convection is triggered, which resulted in the elevated thunderstorms during the snowstorm event. (2) The strongest water vapor transport is located at 700 hPa, the great value belt of water vapor flux is located in the region along the Yellow River in Henan, and there is the abundant water vapor over Henan in this event, which provide favorable thermodynamic condition for the establishment of unstable stratification in the middle level and the triggering of convection. (3) The superposition of upward branches of two secondary circulations in front of the trough provides strong upward motion for the occurrence of thunderstorms and the maintenance of snowfall. The strong vertical wind shear at 0-6 km is beneficial to the development of symmetric instability. The instability energy in the mid-and upper-level is released due to the convergence of southwest wind jet at 700 hPa and the large-scale forcing by the upper trough, thus triggering convection. (4) When the elevated thunderstorm occurs, the intensity of radar echo is greater than or equal to 45 dBz and its top height is over -20 ℃. The "bull's eye" structure and maintain of the convergence rising area are favorable for generating the thunderstorm. The main characteristics of dual polarization radar parameters during the elevated thunderstorm are that the correlation coefficient (CC) is low of 0.7-0.9, the specific differential phase (KDP) is high of 0.5°- 0.7°·km-1, and the differential reflectivity factor (ZDR) is more than 2 dB. Echo intensity over 55 dBz with large KDP of 0.5°-0.7°·km-1 corresponds to the period of frequent lightning and heavy snowfall.

     

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