资源环境科技发展态势分析平台

Mallick et al. (2012, https://doi.org/10.1029/2012JD017555) discovered that subsequent-stroke leaders in natural negative lightning could be more prolific producers of hard X-rays and gamma rays than the first-stroke leader in the same flash. However, they had no optical records to confirm that their subsequent leaders followed the same path to ground as the first leader, as opposed to forging a new path to ground through cold air. In this paper, we present new observations, including optical data, showing that a second stroke produced more detectable X-ray pulses than the first stroke, with both strokes following the same channel to ground. Additionally, we present data for the fifth stroke from a different flash, which show the occurrence of X-ray emission at the onset of the common streamer zone between the hot channels of the downward negative dart-stepped leader and upward positive connecting leader. However, there were no detectable X-rays associated with negative leader steps.

Plain Language Summary: Cloud-to-ground lightning flashes are each typically composed of 3 to 5 strokes. First stroke necessarily develops in virgin (cold) air, while subsequent strokes often retrace the remnants of the channel(s) of preceding stroke(s). Lightning is known to produce hard X-rays during the initial (leader) stage of each of its strokes. Traditionally, first-stroke leaders were thought to be the main producers of X-rays, and subsequent-stroke leaders (developing in warm, low-density air) were thought to be less active X-ray producers. Mallick et al. (2012) observed subsequent-stroke leaders that were more prolific producers of X-rays than the first-stroke leader in the same flash. However, they had no high-speed video images to confirm that their subsequent leaders followed the same path to ground as the first leader, as opposed to forging a new path to ground through cold air. We present new observations, including high-speed video images, showing that a second stroke produced more detectable X-ray pulses than the first stroke, with both strokes following the same channel to ground. Additionally, we present data for a subsequent stroke from a different flash, which show the rarely observed occurrence of significant X-ray emission at the time of attachment of that stroke to the ground.