The physics governing the propagation of lightning leaders and long spark leaders is still not well understood. Positive and negative leaders seem to behave differently. Negative leaders develop in a step manner, guided by the separate luminous structures termed space stems and space leaders. Positive leaders, on the other hand, are generally thought to have no separate luminous structure involved in their propagation. However, a separate luminous structure observed in a positive leader discharge had been reported in recent literature, suggesting that positive leaders may similarly do steps to negative leaders under certain conditions. Here we report the observation of the positive leader step led by a separate luminous structure at high humidity in laboratory lightning-like discharges. We also found the streamer-like common zone connecting the primary leader channel with the separate luminous structure, as well as the bi-directional development of the separate luminous structure. We hope that these findings would contribute to a better understanding of the nature underlying positive long spark leaders and lightning leaders.

控制闪电先导和长火花先导传播的物理原理仍然不是很清楚。积极和消极的领导者似乎表现不同。负领导者在称为空间茎和空间领导者的单独发光结构的引导下以阶梯方式发展。另一方面，通常认为积极的领导者在传播过程中没有单独的发光结构。然而，最近的文献报道了在积极领导者放电中观察到的单独发光结构，这表明积极领导者在某些条件下可能会类似地对消极领导者采取措施。在这里，我们报告了在实验室类似闪电的放电中，在高湿度下，由一个单独的发光结构引导的正先导台阶的观察结果。我们还发现了连接主前导通道与分离式发光结构的流光状公共区域，以及分离式发光结构的双向发展。我们希望这些发现有助于更好地理解正长火花先导和闪电先导的本质。