Lightning nomenclature help

[Dan Robinson]

I am working on a web article about my latest storm obsession, upward-moving lightning discharges. I have run into two distinct manifestations of this type of lightning that I cannot find names for. I am sure they've been classified and named by someone before, but for now I'm referring to them as Type A and Type B. If someone knows the proper names for these I would be appreciative! I would also be interested to know what names chasers have given these types of discharges.

The following is an excerpt from the article along with animations for 'Type A' and 'Type B' upward-moving lightning strokes. I hope to have this article finished and live on the web in a week or so.


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The next set of images show the upward-propagating nature of a ground-to-cloud lightning discharge to a television tower:

Fig. 3: Frames from video of an upward-moving discharge from a television tower near St. Albans, West Virginia.

Ground-to-cloud discharges have been observed in two distinct forms. The first variation, 'Type A', is less common but much more visually spectacular, and consists of a tree-like branch network literally 'sprouting' skyward off of the tip of the structure. As a 'Type A' discharge continues, the number of branches diminishes until only one or two main channels remain to carry secondary return strokes. The second 'Type B' is more common and consists of a single, branchless leader rocketing upward from the structure tip. The video images above have captured a Type B stroke. Although 'Type B' ground-to-cloud strokes show no low-level branching, they usually exhibit upward branching at some point near or above the cloud base. The following animation depicts the two types of upward-propagating 'ground-to-cloud' discharges, Type A and Type B, to a television tower.

Fig. 4: Animation depicting two forms of upward-moving or 'ground-to-cloud' discharges to a television tower. 'Type A' (left) and Type B (right).

 

[Oscar van der Velde]

Hi Dan,

your observations look consistent with the types described in the book by MacGorman & Rust, 1998 (The electrical nature of storms), page 97, the graphs by Berger (1977) / Mazur & Ruhnke (1992).

Type 2b is the upward moving positive leader, which reaches into a negatively charged cloud. A negative downward leader propagating through the inital channel then initiates an upward return stroke.

Type 4b is the upward moving negative leader, reaching into a positively charged cloud. The rest is similar to 2b.

As Richard Orville has explained on the Lightning mailinglist, a negative leader is more likely to step than a positive leader, because if I remember well, in the latter case electrons flow toward the tip of the leader, keeping it concentrated in one path. Refer back to Orville's more detailed explanation to be safe.

This would explain a greater branching in the case of type 4b (A) and less branching in case of 2b (B). However, I believe one needs a LARGE reservoir of uniformly distributed positive charge in order to branch out in all directions. This would be a typical large MCS stratiform region antenna +CG, whereas the type B would be the more common -CG (this nomenclature refers to the net charge brought from the cloud to the ground). I am not sure if one could tell the difference with 100% certainty every time. Borrow/buy or construct an electric field meter!

I have once recorded an upward lightning which appeared not to have a return stroke, or it must have been too weak to discern. Just like negative leaders coming down from the storm without causing a return stroke (I believe I have an example video of that on my website).

Oscar