Lightning – more than meets the eye

By Duane Friend

While we’ve all seen lightning, research is showing more to lightning than it being just a single bolt. There are also electrical discharges that occur above a thunderstorm.

When you see a lightning flash, it typically is part of a larger electrical discharge within the thunderstorm. The record for the longest electrical discharge was almost 8 seconds! In addition, lightning can be much longer than previously thought. One discharge in Oklahoma had a length of almost 200 miles! These may be extreme examples, or part of a process that is not yet fully understood within a storm.

There are common terms for lightning that many people use. For example, sheet lightning is used when a general flash is seen without seeing a bolt. In fact, there is a lightning bolt present, but is hidden by clouds or rain. Heat lightning is said to occur on hot summer nights. Lightning is not caused merely by heat alone. A lightning bolt and storm is present in these cases, but the storm is too far away to be seen or heard, and what is being seen is the ambient light produced by the discharge.

Ball lightning is a very rare occurrence, but does happen occasionally as a glowing ball of light. It is not well understood, and whether it is an actual electrical or chemical process is still being examined.

Positive discharge lightning comes from the top of a thunderstorm, and is more powerful than the common lightning that occurs in the bottom of the storm. It can hit the ground up to 10 miles from a storm, and is likely where the term “A bolt from the blue” comes from.

In addition to these types of lightning, there are types of electrical phenomena that happen at the top of a thunderstorm or many miles above it. The following information comes from the National Oceanic and Atmospheric Administration (NOAA).

Red Sprites can appear directly above an active thunderstorm as a large but weak flash. They usually happen at the same time as powerful positive CG lightning strokes. They can extend up to 60 miles from the cloud top. Sprites are mostly red and usually last no more than a few seconds, and their shapes are described as resembling jellyfish, carrots or columns. Because sprites are not very bright, they can only be seen at night. They are rarely seen with the human eye, so they are most often imaged with highly sensitive cameras.

Blue jets emerge from the top of the thundercloud, but are not directly associated with cloud-to-ground lightning. They extend up in narrow cones fanning out and disappearing at heights of 25-35 miles. Blue jets last a fraction of a second and have been witnessed by pilots.

Elves are rapidly expanding disk-shaped regions of glowing that can be up to 300 miles across. They last less than a thousandth of a second, and occur above areas of active cloud to ground lightning. Scientists believe elves result when an energetic electromagnetic pulse extends up into the ionosphere. Elves were discovered in 1992 by a low-light video camera on the space shuttle.

For more information on lightning and lightning safety, visit the U of I Extension website, “Preparing for Disasters,” at https://web.extension.illinois.edu/disaster/prep.cfm.

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