Upward lightning takes its cue from nearby lightning events

APRIL 12, 2021, by Elizabeth Thompson, Eos

Upward lightning is an uncommon phenomenon, but more common types of lightning, like cloud-to-ground strikes, can make upward lightning more likely. 

Credit: Duncan Rawlinson, CC BY-NC 2.0

In the chaos of a thunderstorm, upward moving lightning occasionally springs from the tops of tall structures. Scientists don't fully understand how upward lightning is triggered; it is likely a combination of multiple environmental factors, such as the background electric field and the structure's height. In a new study, Sunjerga et al. investigate how ambient lightning events near tall structures may trigger upward lightning.

The team created a simplified model of different scenarios that have been observed to occur near a tower before upward lightning. The model was able to explain the mechanism that causes upward lightning to spark from a structure as a result of nearby lightning activity.

According to their simulations, both the relatively slow leader discharge (the precursor paths that lightning will follow) passing above the tower and the much faster return stroke (the bright flash we see as lightning) in the vicinity of the structure can enhance the ambient electric field enough to trigger upward lightning from towers as short as about 30 meters—about 10 stories.

The study confirms the existence of a causal relationship between nearby lightning and upward lightning from towers. Additional research into factors like the local geography, the frequency of each scenario, and the wind speed can help further explain this unusual phenomenon.

This is a screenshot of the article video.

Below is a ytube vid posted by the AGU , Oct. 12, 2012.

https://youtu.be/4q6gHWN8fDE

This is the commentary with the 9 year old vid.

Meteorologists have documented upward lightning, which travels upward from the ground to the clouds, since 1939, but they remain puzzled about how it happens. Now, one research team’s analysis of high-speed video taken in Rapid City, South Dakota, captures a possible clue: a downward flash that preceded most upward lightning filmed by the observers. In this video, which stretches a third of a second to 1-1/2 minutes, leaders descend from the clouds and one on the left connects with the ground at about the 14-second mark, emitting a bright flash of light. That’s the triggering flash. Then, starting at about the 17-second mark, three strokes of upward lightning ascend from nearby radio and TV towers. The upward lightning encounters flickering paths of negative charge called recoil leaders, which spurt electrons back toward the tower and ground upon contact. The researchers filmed this electrical storm at 9,000 images per second.

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