Effects of M‐Components on Needle Activity in Positive Cloud‐To‐Ground Lightning Flashes.

Wu, Bin; Qi, Qi; Lyu, Weitao; Ma, Ying; Lyu, Fanchao; Chen, Lyuwen; Rakov, Vladimir A.; Zhang, Yang; Fan, Yanfeng; Zhu, Baoyou; Liu, Feifan

High‐speed video and electric field records of two positive cloud‐to‐ground ( CG) flashes were used to examine the effect of M‐components on needle activity after the return stroke onset. We observed enhancements of needle activity that were associated with the occurrence of M‐components identified by channel luminosity enhancements both at cloud altitudes and near the ground. Full‐fledged M‐components enhance needle activity via injection of negative charge into the bottom of grounded channel and reversing the direction of the radial electric field at the channel core, similar to CG return strokes. Attempted M‐components, identified by channel luminosity enhancements at the cloud but not near the ground, did not enhance needle activity because of the absence of significant reflection from the ground, which causes electric field reversal at the core. Plain Language Summary: This paper demonstrates the influence of M‐components (current surges enhancing luminosity of grounded lightning channels) on needle activity in positive cloud‐to‐ground ( CG) flashes. Needles are a kind of electric breakdown moving negative charge away from the hot channel core. Full‐fledged M‐components involve a downward (incident) wave and an upward (ground‐reflected) wave. The upward wave injects negative charge into the bottom of the grounded channel, similar to CG return strokes, leading to enhanced needle activity. In contrast, attempted M‐components do not contain an upward (ground‐reflected) wave injecting negative charge into the channel core and, therefore, do not enhance needle activity. Key Points: Influence of M‐components on needle activity in two positive cloud‐to‐ground lightning flashes was studied in detailFull‐fledged M‐components in CGs enhance needle activity through the upward injection of negative charges into the channel from ground levelThe enhancement of needle activity was not observed for attempted M‐components that failed to reach the ground

ELECTRIC breakdown; ELECTRIC fields; CHARGE injection; LIGHTNING; ALTITUDES

Journal of Geophysical Research. Atmospheres, 2025, Vol 130, Issue 8, p1

2169-897X

Academic Journal

10.1029/2024JD041797