Electrical discharges in the overshooting tops of thunderstorms
Electrical discharges in the overshooting tops of thunderstorms
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雷暴过冲顶部的放电
DOI：
10.1002/2016jd025933
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发表时间：
2017
期刊：
影响因子：
--
通讯作者：
E. DiGangi
中科院分区：
文献类型：
--
作者：
D. MacGorman;M. Elliott;E. DiGangi
先前的研究发现，闪电测绘阵列绘制的放电甚高频（VHF）信号源的垂直分布通常在风暴的过冲顶部有一个次极大值。这些源的低速率往往会在过冲顶（OT）的整个生命周期中持续发生，而不是在较低海拔观察到的偶发性明显闪光中发生。本研究考察了VHF OT信号（VHF OT，这里定义为风暴中性浮力水平（LNB）以上每200 m层每分钟≥4个VHF源的持续时间）相对于雷达反射率和红外图像的演变在三个超级单体和两个多单体风暴中过冲顶部的演变。VHF OT在超级单体风暴的红外卫星图像中检测到OT之前就开始了。没有OT观察到在红外图像的多单体风暴，但这种缺乏可能是由于目前的红外成像仪的空间和时间分辨率。VHF OT在18或30 dBZ回波顶部升至LNB上方附近开始，并在其跌破LNB附近结束。在多单体风暴中，对OT的雷达体积扫描太少，无法进行相关分析。在超级单体风暴中，VHF源的最大高度通常小于或等于18dBZ回波顶的高度，并且在VHF OT期间与这些回波顶相关（线性相关系数≥0.86）。
Previous studies have found that the vertical distribution of sources of very high frequency (VHF) signals from discharges mapped by Lightning Mapping Arrays typically have a secondary maximum in a storm's overshooting top. Low rates of these sources tend to occur continually throughout the lifetime of the overshooting top (OT), rather than sources occurring in the episodic distinct flashes observed at lower altitudes. This study examines the evolution of the VHF OT signature (VHF OT, defined here as a sustained period of ≥4 VHF sources per minute per 200 m layer above a storm's level of neutral buoyancy (LNB)) relative to the evolution of radar reflectivity and IR imagery of overshooting tops in three supercell and two multicell storms. The VHF OT began before OTs were detected in IR satellite imagery of the supercell storms. No OT was observed in IR imagery for either multicell storm, but this lack may have been due to the spatial and temporal resolution of the current IR imager. The VHF OT began near the time the 18 or 30 dBZ echo top rose above the LNB and ended near the time it fell below the LNB. There were too few radar volume scans of OTs in the multicell storms for a correlation analysis. In the supercell storms, however, the maximum altitude of VHF sources typically was less than or equal to the altitude of 18 dBZ echo tops and was correlated with these echo tops (linear correlation coefficient ≥0.86) during the period of the VHF OT.