Groups of narrow bipolar events within thunderstorms
Groups of narrow bipolar events within thunderstorms
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DOI：
10.1016/j.atmosres.2021.105450
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发表时间：
2021-04
影响因子：
5.5
通讯作者：
S. Bandara;T. Marshall;S. Karunarathne;M. Stolzenburg
中科院分区：
文献类型：
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作者：
S. Bandara;T. Marshall;S. Karunarathne;M. Stolzenburg
本研究的重点是窄双极事件（NBEs）组，定义为发生在水平10公里范围内±660毫秒内的NBE，位于密西西比州雷暴中发生的正NBE数据集中的大振幅NBE。2个月仅发现15组NBEs，阳性31例，阴性4例。每组2 ~ 5例nbe；4组同时存在正极性和负极性nbe。约一半的nbe具有典型的距离归一化快速天线（FA）电场变化值（4 ~ 15 V/m）和典型的甚高频功率（1000 ~ 45000 W），但17个nbe的FA值为0.2 ~ 2.5 V/m， 17个nbe的甚高频功率为30 ~ 900 W。7个弱nbe的FA值为0.2 ~ 1.0 V/m， VHF功率为30 ~ 100 W。这些发现表明，弱nbe比之前认为的更为普遍。组中的nbe都没有发起闪电，并且（可能有一个例外）组中较晚的nbe都不是由该组中较早的nbe发起的。NBE群的数据符合湍流-大面积空气阵雨(EAS)/相对论失控电子雪崩（RREA）机制，即每个NBE发生在一个独立的1-km3体积内，其中包含许多电场≥3 MV/(m∙atm)的小区域；当EAS/RREA通过1km3卷时，将启动组成NBE的正流。相对于雷暴雷达反射率，23个nbe发生在反射率核心及以上，10个nbe发生在风暴砧高，2个nbe发生在风暴核心附近。我们推测，许多NBE群的出现与动态强对流有关。
This investigation is focused on groups of Narrow Bipolar Events (NBEs), defined as NBEs that occurred within 10 km horizontally and ±660 ms of a located, large-amplitude NBE from a dataset of positive NBEs that occurred in Mississippi thunderstorms. In two months only 15 groups were found, with a total of 31 positive and 4 negative NBEs. Each group had 2 to 5 NBEs; four groups had both positive and negative polarity NBEs. About half of the NBEs had typical values for range-normalized fast antenna (FA) electric field change magnitudes (4–15 V/m) and typical VHF powers (1000–45,000 W), but 17 NBEs had FA magnitudes 0.2–2.5 V/m, and 17 NBEs had VHF powers 30–900 W. Seven weak NBEs had FA magnitudes of 0.2–1.0 V/m and VHF powers of 30–100 W. These findings indicate that weak NBEs are more common than previously thought. None of the NBEs in groups initiated a lightning flash, and (with one possible exception) none of the later NBEs in a group were initiated by earlier NBEs in the group. The data of the NBE groups are consistent with the turbulence-extensive air shower (EAS)/relativistic runaway electron avalanche (RREA) mechanism, which states that each NBE occurs in a separate 1-km3volume containing many small regions with electric field ≥3 MV/(m∙atm); an EAS/RREA passing through the 1-km3volume initiates the positive streamers that comprise the NBE. Relative to thunderstorm radar reflectivity, 23 NBEs occurred in or above the reflectivity core, 10 NBEs occurred high in the storm anvil, and 2 NBEs occurred beside the storm core. We speculate that the occurrence of many of the NBE groups was associated with dynamically intense convection.