On a Possible Mechanism of Reactivation of Decayed Branches of Negative Stepped Leaders
On a Possible Mechanism of Reactivation of Decayed Branches of Negative Stepped Leaders
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DOI：
10.1029/2020jd033305
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发表时间：
2020-11
期刊：
影响因子：
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通讯作者：
Z. Ding;V. Rakov;Y. Zhu;M. D. Tran
中科院分区：
文献类型：
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作者：
Z. Ding;V. Rakov;Y. Zhu;M. D. Tran
使用可见光和红外（3-5 μm）高速摄像机，我们观察到亮度瞬变，重新照亮了佛罗里达两个接近（2至4公里）的负阶梯领导者的腐烂分支。领导分支通过在其尖端踩踏来提供能量，因此，在其下端附近最热，较热的部分通过较冷的部分连接到主干。在闪电先导的建模中，通常考虑单个尖端。相比之下，在本研究中，许多（每个主要分支多达30个）尖端同时活跃，形成一个网状结构，具有下降的多尖端“电离前沿”，其横向尺寸为数百米。前端呈现交替步进，每一步都必然产生一个正电荷波，从前导端沿通道向上沿着行进，就像一个迷你回击。我们推断，阶跃相关波可以在更高海拔的衰变负分支的残余物中引起光度瞬变。这种重新激活的分支反过来可以促进在较低海拔处的进一步领导者步进，如Stolzenburg等人（2015，https：//doi.org/10.1002/2014JD022933）首次报道的。再激活过程可能涉及多个步骤，如大量的活性尖端（每50 μs帧数十个）和以2 μs或更短的时间间隔发生的相应电场脉冲所证明的那样。此外，我们的观察表明，一个衰减分支中的瞬变可以触发（或协助触发）另一个分支中的瞬变。
Using visible‐range and infrared (3–5 μm) high‐speed video cameras, we observed luminosity transients that reilluminated decayed branches of two close (2 to 4 km) negative stepped leaders in Florida. Leader branches were energized via stepping at their tips and, as a result, were most heated near their lower ends, with the hotter sections being connected via cooler sections to the trunk. In the modeling of lightning leaders, usually a single tip is considered. In contrast, in the present study, many (up to 30 per major branch) tips were active at the same time, forming a network‐like structure with a descending multitip “ionization front” whose transverse dimensions were of the order of hundreds of meters. The front exhibited alternating stepping, with each step necessarily generating a positive charge wave traveling from the leader tip up along the channel, like a mini return stroke. We inferred that the step‐related waves can cause luminosity transients in the remnants of decayed negative branches at higher altitudes. Such reactivated branches, in turn, may facilitate further leader stepping at lower altitudes, as first reported by Stolzenburg et al. (2015, https://doi.org/10.1002/2014JD022933). The reactivation process is likely to involve multiple steps, as evidenced by a large number of active tips (some tens per 50‐μs frame) and corresponding electric field pulses occurring at time intervals of 2 μs or less. Additionally, our observations suggest that a transient in one decayed branch can trigger (or assist with triggering of) a transient in another branch.