Enhancement of Green Ghosts Due To Recurrence of Sprite Element

We examined three observations of green emission events (labeled as event A, B and C, respectively) associated with red sprites as captured by amateurs. In all cases, the green emissions were recorded atop of red sprite. Based on the location of causative strokes and background star fields for events A and B, their altitudes are confined between 88 and 100 km, with the maximum brightness at 90.7 and 95.5 km, respectively. Events B and C were lit up for a second time after the recurrence of a sprite element, extending their duration to approximately 1,084 ms and 732.6 ms, much longer than that (about 500 ms) for event A; the intensity of green emissions was also enhanced due to sprite recurrence. It is inferred that the recurrence of sprite elements could affect the ambient condition by further increasing electron density and strengthening the electric field for the ghost production. Plain Language Summary Ghosts are green emissions appearing in the top part of red sprite. As the most peculiar type of transient luminous events (TLEs) above thunderstorms, ghosts were discovered just recently by amateurs with Sony digital SLR camera with relatively high sensitivity and enhanced color imaging capability. In this paper, we analyzed three green ghost events captured during the ground‐based observations by several amateurs in North America. By analyzing the parent strokes and star field information obtained for two events, ghosts were inferred to occur in the altitude range of 88–100 km, with the brightness peaked at 90.7 and 95.5 km, respectively. After examining the observations, we obtained the time‐resolved brightness of ghost events. The duration for two of these events (about 1,000 ms and 700 ms, respectively) is longer than the third one (about 500 ms), primarily due to the recurrence of a sprite element in these two events, which also resulted in a slight enhancement in the ghost brightness. Consequently, it can be inferred that recurrence of sprite elements, which is usually caused by sustained charge transfer in the parent lightning, may influence the ambient conditions by further increasing the electron density and strengthening the environmental electric field. Key Points More observations of rare green emissions associated with red sprites near the bottom of lower ionosphere are presented The duration of green emission for three ghosts examined ranges from 500 to 1,084 ms, and the altitudes range between 88 and 100 km Recurrence of sprite elements wo