Megaflashes: Just How Long Can a Lightning Discharge Get?
November 13, 2019 5:32 AM   Subscribe

Using the Geostationary Lightning Mapper on GOES 16 and 17 (Geostationary Operational Environmental Satellites), Lyons and colleagues probe the limits of how long a lightning discharge can get.

On 22 October 2017, a quasi-linear convective system moved through the central U.S. At 0513 UTC, the GLM indicated a lightning discharge originated in northern Texas, propagated north-northeast across Oklahoma, fortuitously traversed the Oklahoma LMA (OKLMA) [3D Lightning Mapping Array], and finally terminated in southeastern Kansas. ... Combining all available data confirms the “megaflash,” which illuminated 67,845 km2, was at least 500 km long, greatly exceeding the current official record flash length. Yet even these values are being superseded as GLM data are further explored, revealing that such vast discharges may not be all that uncommon.

Check out the last few pages of the PDF of their paper for graphical illustrations.
posted by jjray (11 comments total) 10 users marked this as a favorite
Working on our own version of the Jovian Great Red Spot: do not want.

I like the scale in the visualizations: small being < kA. Kiloamperes; yup. I've worked near and designed around 500 kV 2 kA installations and you do not want to deal with that shit. Conductor spacing is calculated as "how close can we get these things without causing arcing if we drive a service truck between the phases?". I'm kind of glad that humans don't ever build infrastructure in the 10s of kA scale.
posted by scruss at 6:16 AM on November 13, 2019 [11 favorites]

The first sentence of the paper: Lightning is sometimes casually described as “a really big spark.” Scientific understatement at its best. Now I want to spend the rest of the day reading up on atmospheric electrical phenomena to the point of ignoring whatever pops up in the news today.
posted by TedW at 6:54 AM on November 13, 2019 [2 favorites]

Oh wow imagine how much of a 500 mile lightning flash might be visible to someone in big flat Oklahoma? Horizon to horizon?
posted by clew at 9:35 AM on November 13, 2019

I have gone down this particular rabbithole TedW, and it's a joy and a fabulous productivity sink, and Dear God don't do it, please think of the children!
posted by endotoxin at 11:01 AM on November 13, 2019 [1 favorite]

That is really cool, thank you for posting it.
posted by LobsterMitten at 11:28 AM on November 13, 2019

Oh wow imagine how much of a 500 mile lightning flash might be visible to someone in big flat Oklahoma? Horizon to horizon?

I've seen sky and cloud spanning bolts in Arizona that effectively spanned the entire visible sky. Sometimes you get superbolts that involve the very tops of thunderhead anvils and arc out incredible distances or leap out to other cells/clouds.

So the answer is it probably doesn't matter from your perspective on the ground if it's 50 miles or 500 because you can only see so far through the cloud deck and curvature of the earth.

I've also witnessed electrical storms so active and intense it might as well be continuous mega-sized bolts where there was usually more than one sky-spanning bolt going on and tangled with another and you're getting bone-shaking thunderclaps effectively once a second or even less for brief spurts and the sky looks like a billion strobe lights going off at random for an hour solid.

I have also been alarmingly close to major or secondary ground strikes about half a dozen times, as close as about 50 feet. It's incredibly, mind-splittingly loud, and I would not want to be anywhere near one of these oversized strikes.

This is also why supercell electrical storms can be so dangerous. You can get clear sky ground strikes tens of miles away from a cell. It doesn't have to be storming or raining right where you are.
posted by loquacious at 11:57 AM on November 13, 2019 [5 favorites]

posted by bdc34 at 1:37 PM on November 13, 2019

Agreed, loquacious, you have not seen thunderstorms unless you've seen them in the four-corners region.
posted by sjswitzer at 1:55 PM on November 13, 2019 [1 favorite]

The GOES Lightning Mapper also caught a brief glimpse of the meteorite that fell near St. Louis earlier this week.
posted by plastic_animals at 7:31 PM on November 13, 2019 [3 favorites]

I'm kind of glad that humans don't ever build infrastructure in the 10s of kA scale.

Doesn't count as infrastructure but aluminum smelters routinely use 10s or 100s of kAs in their pot lines. It's so weird working on a building a kilometre or two long where big parts of it is plastic, fibreglass or some other non metallic material that isn't effected by the immense amps being conducted. Bus bars several feet in cross section.

Relatively low voltage though.
posted by Mitheral at 9:16 PM on November 13, 2019

> The GOES Lightning Mapper also caught a brief glimpse of the meteorite that fell near St. Louis earlier this week.

Hmm, that's all the cue I need . . . If you can tolerate a Reddit link, yesterday I got curious about the St. Louis meteorite, so I found three videos of the event from three known locations and triangulated the rather exact position, height, speed, etc of the fireball on this map.

(Brief summary: 54 miles in height down to 13 miles, 54 miles cross country & 70 miles as the meteor flies, all in 6 seconds, which make the average speed something like 42,000 mph. Started near Cedar Hill, Missouri, and ended near Americus, Missouri.)

Well, to be precise, that data all came from three videos and one GOES-16 Lightning Mapper snapshot--the one plastic_animals linked above.

I assumed the lightning mapper had caught the moment of brightest flare of the meteorite. So I triangulated the position of that, based on the three ground observations, and (amazingly) it matches almost perfectly with the GOES-16 result.

The interesting thing about the GOES-16 image is that the geostationary satellites are positioned at 22,000 miles height at the equator. So GOES-16 is pretty near Quito, Ecuador, at 22,000 miles altitude.

So when that satellite looks down on Missouri, it's looking pretty slantwise. When it takes a photo of something like a meteor that is 24 miles up, the image of it is projected almost 24 miles over (away from the satellite's location, along the Great Circle path from the satellite to the object) from the point it is actually directly above.

In this case, the Lightning Mapper image shows the meteor smack above New Florence (you can see the lights of the I-70 corridor clearly in the satellite image; New Florence is just a hair north of I-70, just where the light blob strikes).

But in reality it was directly over Berger, about 20 miles south of there.

That is, like, one of those facts about geostationary satellites that I'm sure I had filed away in my memory banks somewhere, but never really quite sank in until I started thinking about "how can that flash from the Lightning Mapper image be so far off from the rest of the meteor track.

Trigonometry is how . . .
posted by flug at 11:28 PM on November 13, 2019 [7 favorites]

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