Characterizing three types of negative narrow bipolar events in thunderstorms
Characterizing three types of negative narrow bipolar events in thunderstorms
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DOI：
10.1016/j.atmosres.2019.05.013
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发表时间：
2019-10
影响因子：
5.5
通讯作者：
S. Bandara;T. Marshall;S. Karunarathne;N. Karunarathne;R. Siedlecki;M. Stolzenburg
中科院分区：
文献类型：
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作者：
S. Bandara;T. Marshall;S. Karunarathne;N. Karunarathne;R. Siedlecki;M. Stolzenburg
来自带宽为16 Hz-2.5 MHz的快速天线（FA）和带宽为186-192 MHz的VHF功率传感器（Log-RF）的数据用于检查负窄双极事件或NNBE。主要的焦点是低空（<8.0 km）的NNBE，引发负云对地（-CG）闪光;以前很少研究低空NNBE。为了比较，还检查了24个高海拔（>8.0 km）NNBE。低空NNBE有NNBE（L）和NNBE（H）两种类型。NNBE（L）具有典型的NBE双极FA波形，而NNBE（H）具有单极FA波形。假设NNBE（H）可能是NNBE（L）的弱版本，其中双极波形的第二过冲部分太弱，无法在FA传感器噪声中检测到。总共有33个NNBE（L）和NNBE（H）发生在平均高度6.2 km（范围4.6-7.8 km），平均距离归一化（至100 km）振幅为0.4 V/m（范围0.06-1.5 V/m），平均VHF功率为130 W（范围1-1300 W）。这些低海拔NNBE的属性基本上是更小和更弱的高海拔NNBE和积极的NBE，启动云内（IC）闪光的相同属性，这些分析表明，-CG闪光比IC闪光更容易启动。对868次CG闪光的FA和Log-RF数据的目视检查表明，只有33次闪光（4%）之前是NNBE（L）或NNBE（H），因此，96%的被调查的CG闪光可能不是从NNBE开始的。
Data from fast antennas (FAs) with bandwidth of 16 Hz–2.5 MHz and VHF power sensors (Log-RF) with bandwidth of 186–192 MHz are used to examine negative narrow bipolar events, or NNBEs. The main focus is on low-altitude (<8.0 km) NNBEs that initiate negative cloud-to-ground (-CG) flashes; very few low-altitude NNBEs have been studied previously. For comparison, 24 high-altitude (>8.0 km) NNBEs are also examined. The low-altitude NNBEs are found to have two types called NNBE(L) and NNBE(H). NNBE(L)s have a bipolar FA waveform typical of NBEs while NNBE(H)s have a unipolar FA waveform. It is hypothesized that NNBE(H)s may be weak versions of NNBE(L)s in which the second, overshoot part of the bipolar waveform is too weak to detect amid the FA sensor noise. Together the 33 NNBE(L)s and NNBE(H)s occurred at an average altitude of 6.2 km (range 4.6–7.8 km), had average range-normalized (to 100 km) amplitude of 0.4 V/m (range 0.06–1.5 V/m), and had average VHF power of 130 W (range 1–1300 W). These low-altitude NNBE properties are substantially smaller and weaker than the same properties of the high-altitude NNBEs and of positive NBEs that initiate intracloud (IC) flashes; these analyses indicate that -CG flashes are easier to initiate than IC flashes. Visual inspection of the FA and Log-RF data of 868 -CG flashes showed that only 33 flashes (4%) were preceded by either an NNBE(L) or NNBE(H), so 96% of the -CG flashes investigated probably did not begin with an NNBE.