One possible mechanism for the formation of recoil leaders and "needles"

A phenomenon known as a "recoil leader" has now been reliably established experimentally. Ricoil leaders manifest themselves as waves of luminosity that move toward the channel of a pre-existing bright leader [Mazur, 1989]. On the other hand, radio interferometers have detected the movement of radio emission sources within thunderclouds toward a possibly existing positive leader channel. This phenomenon is known as "needles" [Hare et al., 2019].

We propose a hypothesis that explains recoil leaders and "needles" based on the phenomena of return corona and return leaders, which were observed during experiments with long sparks (30-60 m) [Lupeiko et al., 1984; Baikov et al., 1988, Mrázek, 1996, 1998].

Qualitatively, the process can be explained as follows. As leaders propagate, a streamer corona in front of the leader tip injects charge into the volume around the leader channel (leader sheath) [Bazelyn & Raizer, 1998]. The leader channel is analogous to a high-voltage wire. As the potential on the "wire" increases, the streamer zone expands, and the charge in the sheath increases. This process continues until the electric field in the "wire" (the leader channel) is balanced by the electric field of the sheath charge. If the potential inside the leader channel drops, the sheath's electric field exceeds the channel's electric field. The electric field reverses, resulting in a return corona and/or return leaders.

This mechanism was confirmed experimentally in [Baikov et al., 1988]. The Marx generator generated a positive voltage of 3.4 MV (rise time 300 μs, pulse duration – 10 ms). The leader moved for 2.2 ms and reached a length of 45 meters. The discharge was incomplete, since the leader did not reach the grounded plane, and the leader plasma decay in the air. Despite the nearly constant voltage (after reaching 3.4 MV), each branching or rotation of the leader resulted in pulsations in the current and leader glow (the sheath exchanged charge with the leader channel). After the leader stopped, the current and glow in the gap ceased, and a dark period began, lasting at least 2 ms. The dark period ended with a series of flashes ("recoil leaders"), the glow zone of which coincided in size with the charge sheath. Each individual flash was accompanied by a current pulse of reverse polarity and a voltage surge across the Marx generator's divider capacitance. The charge neutralized in these flashes was approximately 50 μC.

Similar results at positive voltages of 3-4 MV were obtained on a Marx generator in Prague [Mrázek, 1996; 1998].

 

Baikov A.P. et al. (1988). Electricity, 9, 60 (in Russian)

Bazelyan, E. M., &   Raizer, Y. P. (1998). Spark discharge. Boca Raton, FL: CRC Press

Hare B.M. et al. (2019). Nature, 568, 360

Lupeiko A. V. et al. (1984) Proc. of the All-Union Conf. on Gas Discharge. Tartu: TSU, 1984, v. 2. (in Russian)

Mazur V. (1989) JGR-A, 94, 3326

Mrázek J. (1996). Acta Techn. CSAV, 41, 577

Mrázek J. (1998). Acta Techn. CSAV, 43, 571