Scholten O, Hare B M, Dwyer J, Liu N, Sterpka C, Mulrey K, Veen S Ter
University Groningen, Kapteyn Astronomical Institute, Landleven 12, 9747, AD Groningen, The Netherlands.
Interuniversity Institute for High-Energy, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium.
Sci Rep. 2023 Sep 2;13(1):14485. doi: 10.1038/s41598-023-41218-x.
We have used the LOw-Frequency ARray (LOFAR) to search for the growing tip of an intra-cloud (IC) positive leader. Even with our most sensitive beamforming method, where we coherently add the signals of about 170 antenna pairs, we were not able to detect any emission from the tip. Instead, we put constraints on the emissivity of very-high frequency (VHF) radiation from the tip at 0.5 pJ/MHz at 60 MHz, integrated over 100 ns. The limit is independent on whether this emission is in the form of short pulses or continuously radiating. The non-observation of VHF radiation from intra-cloud positive leaders implies that they proceed in an extremely gradual process, which is in sharp contrast with the observations of other parts of a lightning discharge.
我们使用低频阵列（LOFAR）来搜索云内（IC）正先导的生长尖端。即便采用了最灵敏的波束形成方法，即对约170对天线的信号进行相干相加，我们仍未能检测到来自尖端的任何辐射。相反，我们对尖端在60兆赫时甚高频（VHF）辐射的发射率施加了限制，在100纳秒内积分，为0.5皮焦/兆赫。该限制与这种辐射是短脉冲形式还是持续辐射无关。未观测到云内正先导的甚高频辐射意味着它们以极其缓慢的过程推进，这与闪电放电其他部分的观测结果形成鲜明对比。
