Astronomy Cast

Ep. 424: Lightning

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It turns out that nature figured out how to use electricity long before humans did. Lightning storms are common across the Earth, and even the Solar System. What causes this electricity in the sky, and how can science use it?
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Fraser Cain: Astronomy Cast Episode 424: Lightning. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, the director of CosmoQuest. Hey, Pamela. How are you doin’?
Dr. Pamela Gay: I’m doing well. How are you doing, Fraser?
Fraser: Good.
Hilariously, last week, we talked about cyclonic storms and this week, where I live on the west coast of Canada, we’re about to be smashed by a cyclonic storm; the leftover super-typhoon that is crossing the pacific. So, if you don’t hear me next week, it’s because we just got wiped off the west coast of Canada.
Pamela: We will send paddle boats.
Fraser: Please do, yeah. Yeah. We will definitely have flooding from our river, as we do every year. This happens all the time but – yeah.
Pamela: And you’re in your basement right now.
Fraser: Oh, yeah. I’ve never had flooding in my house.
Pamela: Okay.
Fraser: But we’ve had flooding, you know, from the nearby river that sort of fills up the local park and you can then take your kayak and go – or canoe – and enjoy an aquatic version of the local soccer fields. It’s pretty funny. So – yeah. Hopefully, it’s not that bad. We’ll see. But I’ll let you know how it goes next week, after we –
So now, I get to – I guess the point is I get to experience a cyclonic storm firsthand.
Pamela: So does this mean that, if things follow through, this week you’re going to have massive lightning storms?
Fraser: Nope.
Pamela: Okay.
Fraser: We never get lightning here. But –
Pamela: You’re right, you don’t.
Fraser: And let’s find out.
So it turns out that nature figured out how to use electricity long before the humans did. Lightning storms are common across the Earth and even the solar system. What causes electricity in the sky and how can science use it to understand the world around us?
Alright, Pamela – Yeah, so you were just talking about this in the intro, which is that, you know, we’re about to get lightning here but we’re not; we never do. And, in fact, this is one of the things that my wife is so surprised is – is that, she comes from Texas, where lightning storms are just a regular basis and they have these huge lightning storms that roll in, sometimes every couple days.
We maybe hear lightning here on the west coast of Canada once a year, maybe twice a year; almost never.
Pamela: Yeah, there is a fabulous graphic that we will try and put up in the show notes that I know you have in Universe Today. It’s on Wikipedia. It’s kind of all over the internet because it’s a map of the density of lightning strikes all across the planet. And you look at it and it’s just like the universe hates North and South America, Africa and the Asia-Pacific area. But, like, Europe and the non-Asia-Pacific parts of Asia, they’re good. No lightning strikes.
And it all has to do with where we have an atmosphere that experiences a lot of friction. Now, I have to admit, this is one of those shows that I kind of picked because I live in tornado alley and so the –
Fraser: Something was going on in – out your window – and you’re like, “Hmm. Maybe that’s a show topic.”
Pamela: That’s exactly – Right. So, Susie had pestered me, “Hey, we need a topic for Friday.”
And I literally looked out the window and there is this wall of dark, evil of – with punctuations of lightning, roiling across the sky toward us. And I’m like, “We can do lightning this week.”
And I have to admit, though, the first thing I learned in prepping for this show, that at the age of 42, I’ve been misspelling the word lightning my entire life.
Fraser: What? Did I misspell it?
Pamela: I don’t know if you did. So –
Fraser: Light – ning.
Pamela: Right. So, a lot of people pronounce it light-en-ing. But there’s –
Fraser: Light-en-ing –
Pamela: And –
Fraser: – which is where light levels go up, where you brighten up a scene in your camera.
Pamela: And it’s also a medical term, that I’m not going to go into, that involves things with pregnancy. So, if you spell it that way, Spell Check will never, ever –
Fraser: Ahh.
Pamela: – let you know.
Fraser: Right.
Pamela: So you can go –
Fraser: And so you’re constantly spelling it lightening but it’s really light – ning.
Pamela: Ning. So there is no E involved. So let this be a lesson for everyone out there. Lightning and thunder, there is one E in that combination and it’s in thunder, not in lightning.
Fraser: Thun-e-der.
Okay. So you mentioned that it’s like regions that are of higher friction. So, what’s going on? What is causing the lightning?
Pamela: So, no matter what world you go to – and this is the cool thing, is physics here is the same as physics everywhere. When you get a turbulent atmosphere, this is an atmosphere where you have – you either have convective cells rising or you have some sort of a wind pattern, where things are getting jostled. You end up with different – different molecules forming the atmosphere.
So, for instance, if you have a cold front, you may have ice up in the atmosphere. You may be fine, down at ground level, but think of all those nights when you’ve looked up and there’s been a halo around the moon. That’s because there’s ice crystals in the atmosphere that are refracting that light.
Now, if those ice crystals that have formed in the atmosphere start rubbing up against each other due to – well, turbulent convective cells, high speed wind; all of those things that happen when you have a cold front mixing with warm air, or a warm front mixing with cold air, all of this mixing of air of different temperatures that has moisture involved, ends up with ice particles or you can even end up with slush in the atmosphere.
These particles rubbing up against each other – it’s the same as a balloon against a wall that you’re rubbing up and down – and you end up with charge on the two different surfaces that’s different charge. This is triboelectricism, which is like my favorite word – triboelectric. When this happens, you end up with an exchange of charge and you can end up with a whole bunch of charge of one type on the bottom of a cloud and of another type on the top of a cloud. And as this potential gets bigger and bigger and bigger, eventually the charge has to go somewhere.
Fraser: And so, I guess, the molecules that are bouncing into each other are just the atmospheric – just whatever’s in the air, right?
Pamela: So, it’s usually –
Fraser: Oxygen, Nitrogen –
Pamela: – you have dust particles seed moisture around them and form ice or slush.
Fraser: Right.
Pamela: Interestingly, ice tends to, like, get positive charge all over it but, if you instead end up with, like, moist slushy gook in the atmosphere, think snow.
Fraser: Okay.
And so you’ve got this, sort of, difference of charge that’s kind of happening in the atmosphere.
Pamela: Mm-hmm.
Fraser: How does that then turn into the lightning that we experience?
Pamela: It – it’s very simply, the air is trying to be an insulator, trying to keep the negative charge that is usually at the bottom of the cloud away from the positive charge at the top of the cloud. Or, even better, you end up with induced charge on the ground. So the air is trying to prevent the charge from jumping from the cloud to the ground, or from the cloud somewhere else in the cloud, but eventually, the charge potential will get so great that it overcomes the atmosphere’s ability to act as an insulator.
And the first thing that happens – and you may have seen this. I know I’ve had the misfortune of seeing it a little bit too close. You’ll sometimes notice things – pointy objects, like lightning rods, start to get a glow around them –
Fraser: No. No, we’ve never seen this.
Pamela: You need to travel more. It’s awesome and terrifying and awesome!
Fraser: I could miss that. That’d be alright.
No, actually, I was – I was doing a show in New Mexico, about back in June, and we were going to be doing, like, a live – it was at the Bandelier National Monument – and we were going to be doing some, like setting up some telescopes and we were going to do some live viewing and I was going to give a talk.
And a lightning storm moved in and there was lightning strikes all around us and the – and the park rangers had this gadget that told them when a lightning strike had just happened and how far away it was. And it was sort of freaking out and so they were like, “Okay. We all have to go inside now. We can’t really be out here and be standing out,” you know, “Definitely, Fraser, you can’t be out on a…” you know, “…out on a stage while there’s lightning going off all around us.”
So – so I – but I didn’t stick around to look for things starting to glow. Had I, I think I would have panicked.
Pamela: So, I tend to get obsessed with getting my camera set up and fail to notice the world around me sometimes.
Fraser: Yeah.
Pamela: And, back when I was a graduate student, I was observing at McDonald Observatory and I had with me a fabulous undergraduate, who had what may have been the worst observing run for a first observing run, ever.
One of the things that happened was, we were out on the catwalk of the 107-inch at McDonald. I was setting up my camera to take pictures of distant thunder storms that were taking place above forest fires off in the distance – which the undergrad was the first person to spot – and, while I was setting up my camera, she’s just like, “Is that the lightning rod over there?” and she had this fabulous Arkansas accent. And the lightning rod was buzzing slightly. And all the hair on our arms was up but I was so focused on getting this photo that I had failed to notice any of this and –
Fraser: Can’t talk, I’m doing science.
Pamela: So we go inside – and there’s double doors out to the catwalk – and we had the double doors open. So I just set up my camera straight inside the double doors. And as soon as I was done setting up my camera, the 82-inch telescope just a couple hundred feet away from us, got totally nailed with lightning. And, yeah.
Fraser: So – okay. So, before you freaked me out, we were talking about how you’ve got this, sort of, difference in charge in the cloud layer that – that then, you know, as just regular electricity, the – you know, if you’ve got too many – you know, too much of a charge in one location, that charge wants to balance out and jumps – wants to jump to the other location. That could be from cloud to cloud or that could be from cloud to ground.
Pamela: And, in general, the bulk of the lightning in central locations is cloud to cloud and the bulk of the lightning in more northern locations is cloud to ground. And this is because of the temperature differentials.
So you have lots of different things at play. You have: How low is the bottom of the cloud compared to the ground? You have: What is the temperature differential between the cloud layer and the ground? You have: How high is the cloud?
In some cases, the clouds will be only a couple of kilometers up, at their lowest level, but then they’ll be a score of kilometers in height, from bottom of cloud to top of the cloud. And all of these things factor in to figure out: Is it going to be more cloud to ground or more cloud to cloud?
So, one of the – my favorite things that I ran across is, if you are someone in, like, Norway, which has all of these convective cells and temperature differentials and is at a very high latitude, you’re going to get – 50 percent of the lightning is cloud to ground.
Now the other thing is, there’s certain hotspots on the planet that average hundreds and hundreds and hundreds of lightning strikes per year. Congo is one of those places that has all of the right thermal conditions and very active volcanoes. All of these things pile up at once. And, for the most part, we’re able to count the cloud to ground lightning strikes but, because they have less of a temperature differential there at the equator, they’re only getting, like, 10 percent cloud to ground strikes.
So there is just phenomenal amounts of lightning in these hotspots like Congo; there’s some places in Brazil, north of Florida. There’s just hotspots on the planet where lightning happens.
Fraser: Yeah. And places like where I live, where they don’t happen all the time – even though we get rain storms, we just don’t get thunder storms in the same way.
Pamela: But – and it’s because you’re not getting the active convective cells. So what’s happening is, you have warm ground air filled with moisture rising up, cooling; cool air then sinks. And so this sets up a turbulent atmosphere. And all of this action – it’s this action that causes the lightning to occur.
You guys just get everyday – “Huh, the atmosphere is saturated with water. We’re going to let it fall out of the sky now.”
Fraser: Right.
Pamela: It’s a little bit gentler.
Fraser: Yeah. Yeah, totally.
Now, one of the most, kind of, amazing phenomena is when you’ve got, like, some kind of volcanic eruption. That’s where you see some of the most, just mind-bending lightning ever.
Have you seen some of those pictures of, like, Ecuadorean volcanoes with crazy plumes of smoke and there’s – and there’s, like, lava coming out of the volcano and then there’s just lightning all through.
So why is that happening?
Pamela: So this is called “Pyrocumulus Clouds.” I love this word. I’m sorry. I’m far too excited about this topic.
Fraser: Yeah, clearly.
Pamela: Lightning is just fabulous.
So, with Pyrocumulus Clouds, you end up – either with forest fires or volcanic activity – you end up with all of these particles in the atmosphere that, when you rub them together, you end up with electricity building up, charge building up. So you have ash, you have pumice, you have soot; all of this different particulate matter getting turbulently mixed in a hot, moist environment causes charge to build up and it can also sometimes facilitate the discharges happening more rapidly because the potential’s a little bit different.
So, if you have just, like, your normal, everyday, big old angry thunder cloud, it’s water vapor and air that is forming, that buffer between the bottom and the top of the cloud or between the bottom of the cloud and the ground, that the electricity has to get over. You end up with these charge channels forming, where – this is where you have the St. Elmo’s fire that I was talking about – that’s saying: Hey, we have a channel where things are starting to get ready to form. Then you have a channel coming down from the bottom of the clouds, when these channels meet. You end up with massive discharge. This is the lightning.
Fraser: Yeah. When you see those, like, time-lapse or, like, you know, slow-motion videos of the lightning strikes, you actually can see that. You can see the current reaching up from the ground at the same time that the current is reaching its way down from the sky. When those two finally find a pathway, that’s when the lightning strike happens. It’s amazing thing to see.
Pamela: And so these are called your upward and downward streamers. And they have different charge because you have the positive being induced on the ground and the negative on the bottom of the cloud. Now you end up with a completely different potential barrier to overcome and you have all of these particles that can help channel the lightning through the volcanic or smoke-induced clouds and this just increases all – it’s the kind of thing that we don’t fully understand because there’s too much going on, which is, I think, why I, as a scientist, get so excited about it because we don’t fully understand it.
Fraser: Also, it’s kind of scary and dangerous.
Pamela: And explodey.
Fraser: Explodey.
So now, Earth is not the only place that experiences lightning.
Pamela: No. So, one of the things that we’ve talked about the last few episodes is how we end up with weather in multiple worlds. Now, with both Saturn and Jupiter, you end up with convective cells in the atmosphere, you end up with temperature regions mixing, you end up with storms and you end up with massive amounts of lightning on Jupiter and lesser amounts but we still see storms occurring on Saturn.
And it’s just, again – it’s these temperature variations leading to convection cells. You have water vapor in the atmosphere. Things rub together, get charged; discharge lightning.
Fraser: So, what places in the solar system – if you were to fly your Carl Sagan spaceship quickly across the solar system, where could we find examples of lightning?
Pamela: Anywhere where we have convection and water moisture. So, the thing is, it’s been theorized to occur just about everywhere. It’s hard to just happen to be catching it on a spacecraft just right. The first time we saw lightning on Saturn was in 2009. So there could be lightning pretty much everywhere that has an atmosphere. So, like, Mercury, not so much. Venus –
Fraser: But Venus, for sure. Mars –
Pamela: We’ve seen it on Saturn and Jupiter. We haven’t seen it on Mars so far, that I know of, but there’s no reason that we wouldn’t see it on Uranus and Neptune as well, with the storms they have and the water vapor that exists in their atmosphere.
Fraser: Titan?
Pamela: Titan – maybe. I don’t think the convective cells are violent enough.
Fraser: Right.
No, there’s actually this great – if you go to, like, NASA’s SoundCloud account, they’ve got links to all of their, you know, various audio recordings that they’ve got. And one is, I think, lightning in Jupiter.
Now, they’re obviously – they’re not actually –
Pamela: Saturn, they have one too.
Fraser: They have one for Saturn too, yeah. And it’s not like they’re actually, you know – they’re not recording these things with a microphone, of course, because the space wouldn’t translate the sound. But they are sort of taking a – you know, they’re, like, recording the – I guess, the polarity of the atmosphere at a certain point and then they’re able to detect when these – when these lightning strikes are going off and they’re able to play these sounds, which are pretty cool.
Pamela: And we can see this in other forms of light than optical. I mean, here on Earth, we’re used to the flashes that occur if you’re in the right part of the planet and we see it with our eyeballs. A lot of us grew up learning to count the second between seeing the flash and hearing the thunder so you could tell how far away the storm was.
But, if you have a radio, you can hear the burst of static associated with the sudden ionization as plasma is formed in the atmosphere. If you have an x-ray detector, you may be able to detect he x-ray streak given off in the process. This is violent and shows up all across the electromagnetic spectrum in different ways.
Fraser: So I’ve got – I’ve got a sound clip here. This is going to be a first. I’m going to try and – Oh, no. You know what? There’s no way that I can play this through the actual podcast. So I won’t actually be able to – unless –
Pamela: We’ll link to it in the show notes.
Fraser: Yeah, unless Chad is going to be able to do it. Maybe he’ll hear this and, when he’s doing the edit, he’ll put this in. So I’m going to put this in to the Livestream and then – and then I’m not sure what we’re going to do for the show. Maybe he’ll just edit out that I even said it.
So here we go. Listen to this. Alright. So, hopefully, the – there you go. So, I think – alright. Hopefully, people who are on the Livestream were able to hear the sound of the lightning on Jupiter, which is pretty cool.
So now, what do we do if we are in a place where lightning is going to be happening?
Pamela: So, first of all, you want to be the shortest thing around.
Fraser: Right. So I don’t have to run faster than the– faster than my – than the bear, I just have to run faster than my friends.
Pamela: Exactly.
Fraser: Yeah.
Pamela: Exactly. So, electricity’s lazy. It wants the easiest path between two different charges. So, if you have your negative cloud bottoms, if you have induced charge on the ground, it’s going to find the shortest path to the ground, which means the tallest object. So, either the tallest tree on a hill, the only golfer on a golf course; it’s going to go whatever path makes it easiest to get that charge dispersed.
Fraser: Right. I kind of imagine that there are these, like, – like I said, when you saw that little – when you watch that time lapse or that – sorry – that slow-motion version of it, you can see those little tendrils.  There’s tendrils kind of coming up from everywhere: You, the trees, the – and it’s, like, whichever ones connect, that’s where the bolt – that’s where the bolt of lightning finds its way back down. So you just don’t want to be on the pathway.
Pamela: And, if you’re not sure entirely how to get away from the pathway, there’s a few stupid things you shouldn’t do.
One thing that a lot of people have tried doing, which isn’t so good, is, like, spreading yourself flat on the ground to try and make yourself as small as possible in height. Now, the problem is, you have just increased the surface area of your body that is connected to the ground and the problem is, if the ground near you is struck, that electricity is going to flow through your body – and if it flows over your heart, it can disrupt your heartbeat, which could kill you, which is bad.
So, one of the things that I learned when I was a kid, is kneel down, keep your two feet on the ground and don’t touch anything else because, hopefully, that will prevent electricity from going through your heart.
So – yeah, things like that are best avoided. Don’t grab on –
Fraser: But – so, like, if there’s a tree, don’t go near the tree.
Pamela: Don’t go near the tree. Do not put, especially, your left hand on the tree while your feet are on the ground.
Fraser: Right.
Pamela: Fairly certain death.
Fraser: Right.
But then – but, I mean, you don’t want to be so far away from the tree that – that you now form – you become the tallest thing in the region, right?
Pamela: Right. So, in general, you want to go away. Going into your car is actually a fairly fabulous place to go because, again, electricity is lazy. If your car gets struck by lightning – and it’s not like 100 percent cloth and fiberglass, which some current cars are – if it’s like a normal metal car, the electricity will go on the outside of your car and you’re safe on the inside. This is what’s called a Faraday cage effect.
In fact, you could be inside of a giant birdcage and, if the birdcage was actively getting struck by an angry Zeus, you could run your hand along the inside of the birdcage while the lightning hitting the birdcage would run down the outside of those exact same wires.
Fraser: Wow.
Pamela: And, if you happen to ever visit the city of Boston, the Boston Museum of Science has an amazing indoor lightning storm demo that they do, where they stick someone in the moral equivalent of a birdcage and don’t kill them.
Fraser: Nice. That’s convenient that they don’t kill them.
Pamela: Death is bad.
Fraser: Right. But, I mean, you know, if you’re going to be in your house, make sure you’ve got a lightning rod in the house that connects to the ground.
Pamela: Grounding rods are a good thing.
So, one problem that I’ve personally run into, Massachusetts does get totally hit with lightning. And so, while I was living in Somerville many years ago, the television antenna for our building was struck by lightning and the electricity happily went down it and into the back of my television and then into the electrical system of the house and fried everything attached to that particular surge protector.
So, yeah, you want to have something that is taller than your TV antenna and the ground goes to the ground, not to part of your house.
Fraser: So, one thing – and I don’t know if this is a myth. I actually don’t know this – if this is true. So, I’m just – you know. They have in – like various science fiction shows, you’ve got, like, some kind of spacecraft moving through a nebula or something like that and there’s, like, lightning going on. I think it was, like – Wrath of Khan, I think they had that, –
Pamela: Yeah. I think it was Wrath of Khan –
Fraser: – as it was moving through the Mutara Nebula.
Now, we’ve already discussed the fact that – you know, if you were passing through a nebula, you wouldn’t even see it. You wouldn’t even know you were inside of it.
But are there any situations that are not in an atmosphere, that you can get some kind of electricity or lightning going on?
Pamela: So, the speed at which the lightning discharges and the frequency at which they’re taking place in The Wrath of Khan always kind of bothered me.
But electric fields permeate space. They’re generated by all sorts of different things and, if you end up with any potential differential for whatever the reasons are – shock waves from a star, stellar winds from something that is young and angry – you can get lightning bolts. It’s just a matter of, are they going to be that dozen of lightning bolts per hour that you get with a good, old fashioned, roiling storm going across the surface of the Earth? Or is it going to be more like slow build, slow build, slow build, discharge, wait a few thousand years?
Fraser: Right.
And I wonder what kinds of environments around, like, rapidly rotating things like neutron stars, black holes, things like that.
Pamela: Well, those are all compact bodies that don’t really have clouds of material, necessarily, around them, except for that accretion dust.
Fraser: Yes.
Pamela: And so, this is something where – I am not the kind of astronomer you ask questions about magnetic fields and dust to –
Fraser: Yes.
Pamela: – but now I’d love to corner someone like Bryan Gaensler and say, “Bryan, tell me about where you can get lightning storms.” Because, you know, all you need is that electric differential.
Fraser: Yeah. That’s super-interesting.
Alright. Well, thanks a lot, Pamela.
Pamela: My pleasure.
Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com. Tweet us @astronomycast. Like us on Facebook or circle us on Google Plus.
We record the show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern or 2030 GMT. If you missed the live event, you can always catch up over at cosmoquest.org or our YouTube page. To subscribe to the show, point your podcatching software at astronomycast.com/podcast.xml, or subscribe directly from iTunes. Our music is provided by Travis Serl, and the show was edited by Chad Weber.
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Duration: 30 minutes

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