Credit: XU Chen
A team of researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences (CAS) has reported the first observational evidence of lateral negative re-discharges occurring along negative leader channels—a phenomenon never documented before. Published in Geophysical Research Letters, the discovery sheds new light on how lightning channels stay electrically active and how their structures evolve around the moment of a return stroke.
Until now, scientists had only observed negative-polarity lateral breakdowns near the tips of positive leaders, leaving a significant gap in understanding how negative channels behave. This new study fills that gap with high-resolution evidence captured during a positive cloud-to-ground lightning event over the Qinghai–Tibet Plateau.
To uncover this rare phenomenon, the researchers used a self-developed very-high-frequency (VHF) lightning interferometer, featuring sub-microsecond temporal precision and spatial accuracy within a few tens of meters.
By combining VHF interferometric imaging with ground-based electromagnetic measurements, the team detected repeated short-duration lateral re-discharges along pre-ionized negative channels, appearing both before and after the return stroke.
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Before the return stroke, the positive leader progressed steadily while the negative leader weakened. During this stage, small, needle-like lateral re-discharges emerged along nearly the entire stretch of the horizontal negative channel.
These short bursts traveled toward the negative leader tip at about 8 × 10⁴ m/s, producing VHF radiation intensities similar to those traditionally associated with needle discharges near positive leader tips.
After the return stroke, the researchers observed another wave of rapid discharges sweeping through the existing negative channels, as well as fresh lateral breakdowns extending into previously un-ionized regions. These post-stroke processes quickly lengthened the negative channels and played a key role in sustaining the long-duration continuing current by helping preserve channel conductivity.
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“What really caught our attention,” said Prof. Qie Xiushu, the study’s corresponding author, “was the connection between these re-discharges and the evolution of channel potential. Gradual potential changes before the return stroke tended to revive weakened branches, while sudden increases afterward triggered entirely new breakdown paths.”
The findings suggest that the rate and magnitude of channel potential change largely determine whether a lateral re-discharge reactivates an existing channel or initiates a new one. This mechanism provides critical clarity on how negative-polarity channels evolve around the return stroke and how conductivity is maintained throughout the continuing-current phase.
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