lightning question

[Doug Raflik]

Last night I was photographing lightning in SW Wisconsin, and all the lightning in the storm was different from any other lightning I had seen or photographed in the past. There was no branching. No return strokes that I saw. Most of them went in straight lines. They seemed brighter than normal, and the thunder was incredible. I was told on another list that these were positive CGs from an inverted polarity storm. Just wondering how this happens, and how rare is it. Due to the lack of branching, the thunder lacked the crackle before the main BOOM that we are used to hearing. The crackle being the softer thunder of the branched lightning closer to you, getting to you sooner than the main channle. This thunder was just a BOOM, like an explosion. Very awesome to hear it like that. Here are a few pics from last night... BTW, what do you think is going on in that last picture at the bottom of the bolt?

Thanks for any info you can give me about this type of lightning.

Doug Raflik

 

[John Diel]

AMS defines streak lightning as this:

streak lightning—Ordinary lightning, of a cloud-to-ground discharge, that appears to be entirely concentrated in a single, relatively straight lightning channel.
Compare forked lightning, zigzag lightning

That's about the best I could find on it.

 

[Doug Lee]

I remember reading somewhere that an ionized path develops between the cloud and the ground, and the lightning follows this path. I believe that wind will bend the path and this accounts for crooked and forked lightning.

Was the wind relatively calm when you took those pics?

 

[Bill Schintler]

"Positive" versus "negative" lightning...

The great majority of lightning originates from a negatively-charged cloud base, and strikes the ground or objects having a relative positive charge. This is referred to as “negativeâ€￾ lightning. A small minority of lightning originates from portions of the cloud high in the storm, such as from the anvil. This part of the cloud carries a positive charge, and this type of lightning, “positiveâ€￾ lightning, is typically much more powerful and longer lasting (duration of stroke) then the more common negative bolts. Because of larger power released as well as the longer duration of the energized channel, the sound produced by such lightning is much louder and deeper (longer duration of channel = more lower audio frequencies in the spectrum of the thunder). The sound of a close positive stroke is often like that of a large explosion. As far as the lack of forking is concerned, I’m not sure what might explain that.

[FONT=&quot]- bill[/FONT]

 

[Jeff Snyder]

The displacement of the ionized channel by the wind should be negligible. For example, suppose the wind is from the west, starting at 0 m/s at the ground and increasing to 20 m/s (~45mph) at 2km. At any rate, let's also suppose that the lightning channel is visible for 1 second (some are much shorter, some, with multiple return strokes, can be longer). So, in that 1 second, the part of the lightning segment at 2km above ground has moved 20m. Assuming the strike is more than a mile or two away, I don't think you'd even be able to discern the 20 m movement. In addition, for a multi-second exposure, the picture would show the 2km portion of the strike as just a "fatter" section, not an actual displacement. Despite time-scales on the order of milliseconds when it comes to most stepped leaders and pre-return stroke processes, extremely strong winds may have an impact on the lightning channel, I suppose. As for forked vs. streak... I have no idea. LOL.

For what it's worth, I agree that the strikes above may positive-flash strikes. However, that still doesn't explain why the strikes would be non-forked (or show little or no tortuosity). I'm not sure that we understand stroke multiplicity (number of return strokes) very well, either.

Field experiments such as STEPS have indicated that inverted polarity storms are not entirely uncommon, particularly in the high plains region. As the name suggests, inverted polarity storms show a dipole or tripole structure that is opposite that observed in most other thunderstorms. In such a storm, the primary positive charge resevoir is near the base of the storm, with the primary negative charge resevoir in the mid- and upper-levels of the storm. A Google search turns up a couple good publications on inverted polarity storms. Even for "regular" polarity storms, some storms have been observed to produce nearly all positive-flash lightning, while other storms have been observed to produced nearly all negative-flash lightning.

I've been interested in this forked vs. streaked lightning too. I remember one chase in far sw MO a couple of years ago... Gabe Garfield and I were chasing an HP supercell, and the CG rate was very rapid. Interestingly, almost all of the CGs we saw were extremely bright and short flashes (i.e. very low multiplicity), with little or no forking. On many other chases, the CGs were more forked and had higher multiplicity. For that matter, I remember several chases from 2003 that featured tornadic supercells with extremely limited CG lightning activity (May 8 2003 in NE OK and se KS comes to mind). What gives? I have no idea.

New observing platforms will allow us to see things that we've never seen before, and heck, maybe that'll give us a clue as to how lightning develops in the first place.

 

[Dan Robinson]

The branching vs non-branching leader is a function of the polarity of the leader tip. A good discussion on this subject has been ongoing on the lightning list (unfortunately which is not public, but you can sign up at http://tech.groups.yahoo.com/group/lightning/ ).

 

[Willie Dines]

These particular lightning bolts look eerily familiar, I'll briefly explain

About 4 years ago, there was a large severe thunderstorm that came through here, and boy, it was seriously charged up and ready to rumble, every 1 - 3 minutes there were lightning strikes, but because of my location (The storm was moving N and I was situated ESE of the main tower), the lightning strikes that I was witnessing, were positive strike, as I knew by not only the explosive boom, that the thunder had, but also because the part of the storm that I was mostly under, was the anvil's overhead reach, and each CG, that I had witness, except for a few, weren't forked, they were also quite bare looking, but still had a serious load of voltage, from how bright the CG's were

There were also some negative CG's, but only about 10% of the strikes were negative and suprisingly only about 30% of the were forked, the rest were all branchless CG's, which I found to be very weird, but at the same time, I thought that it was very cool, especially since there were CG Strikes that were as close as 1/4 mile away, and there's nothing that I love the sound of more, than really loud thunder

The idea of inverted polarity storms, is certainly very intriguing and makes alot of sense, but I have wondered if some positive CG's have travelled down through the core of the tower, from the ground, to the anvil (Remember, lightning actually starts forming from the ground, and works it's way up to the connecting charge in the storm base, but it happens too fast for human eyes to detect this, as it's an almost instantanious movement) therefore the sorrounding could density would soften the sound of the thunder a little, but you would still have a large "Boom" due to the extra amount of extra superheated air expanding, because the extra amount of voltage that's being blasted through the air.

No matter what, the lightning pics are AWESOME , thank you Doug for posting them

Willie