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Lightning Can Strike Twice...at the Same Time

NSF Award:

EAGER: Multi-frequency Studies of Lightning Initiation and Propagation  (University of Mississippi)

Multi-Frequency Studies of Lightning Initiation and Propagation  (University of Mississippi)

Digital High-Speed Spectroscopic Lightning Studies  (Texas A&M Research Foundation)

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Scientists have long known that lightning flashes are composed of multiple strokes, and that these strokes sometimes occur in different locations. But a team led by researchers at the University of Mississippi has described a unique type of lightning stroke.

Termed "upward illuminations," these strokes occur within a few thousandths of a second after the start of a normal stroke--a very short time even for lightning. The strokes follow a separate path to the ground and connect to a different ground location as far as a few miles away from the normal stroke of the same lightning flash.

Usually, the multiple strokes of a lightning flash are separated by tens of thousandths of a second or more, and one stroke ends long before the next one begins.

None of the upward illuminations found in the study were detected by the two operational systems designed and used to locate lightning return strokes. However, the events were documented on high-speed video and detected by two research-grade systems. The strokes had electrical currents of a few thousand amps--large enough to cause possible damage to equipment and people on the ground.

This research, conducted at Kennedy Space Center, will help investigators discover ways to improve detection of these previously unsuspected strokes to allow NASA personnel to check vital equipment near their ground connections.

Because the upward illumination stroke can occur in a different location while the previous stroke is still carrying electrical current to the ground, lightning channels are likely not all connected within a cloud. Since the upward illuminations are comparatively weak, short, slow and difficult to detect, the results of this study also show that more locations on the ground may be subjected to damage by one lightning flash than was previously known.

This study is part of ongoing research using time-correlated data from many types of sensors to understand how lightning starts and why it travels where it does both inside and outside clouds.

Image

  • high-speed video stills show multiple strokes from one lightning flash hitting the ground
High-speed video stills capture a new kind of lightning stroke.
Maribeth Stolzenburg et al., University of Mississippi

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