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268: Cakepan Interferometry


Hello. And welcome to embedded. I'm elise. You're white here with Christopher white. I remember I've been asking guests for lightning facts has been going so well, but this week I expect it to go very, well, our guest is Eric Rooney, and he's an expert on lightning. Be prepared for shocking episode. Eric. Eric welcome to the show. Hi, thanks for having me. Could you tell us about yourself as though we just met after John lemans GIO cast podcast. Yes, sure. I I work at Texas Tech on the the faculty I teach in a an atmospheric science program and grew up in Wisconsin originally, and did my graduate work and undergraduate as well at the university of Oklahoma and spent a couple years in Maryland after finishing my PHD and wound up in sunny Lubbock, Texas, studying lightning studying lightning in meteorology. Yeah. Texas is probably a good place for. Yeah. It is. Yeah, it's nice to live in the place that that has the thing you want to study, and what's me up run an instrument here and get graduate students involved in in that that instrumentation work. So now, we want to do thing that has been getting into trouble, which is lightning round where we ass. Short questions and we want short answers. Okay. Christopher do. You wanna start? Sure. Benjamin Franklin, and the kite thought experiment or write up of scientific apparatus. Up of scientific apparatus back to the future thought experiment or write up of scientific apparatus thought experiment. Blinding fact fiction or the coolest thing ever. Fact, probably. Sprite a diminutive ethereal creature a two dimensional bit map that is integrated into a larger seen on computer graphics or a weird thing that happens above clouds. Yes. What is the most shocking fact that you know? Oh boy. Did you get for letting me write these? Do I go with a pun or not? I guess that's the question here. Let's see. Lightning's many thousands of oats. That is shocking. Fact, it's good that somebody knows that. Yeah. If you were playing legend of Zelda would endure you it was lightning around. You would have in the rubber pants actually help you as you were standing in the lake or wood rubber pants. Not really do anything. Probably not help you too much. Okay. River pants the river shirt in the rubber boots the helmet to there's. Yeah. I'd rather be in a metal cage. Okay. So let's get some more detailed in possibly useful questions. Let's see do you want to talk about your career first or do you want to go through the list of many listener questions about lightning? Well, I we can I guess start with career since we just just did the meet-and-greet. Okay. So you work on lightning detection as well as as as meteorology. Yeah. That's right. My my degrees really in meteorology, and that makes me a little bit unusual in a scientist that study lightning. A lot of folks I get into it from from physics or electrical engineering background because the instrumentation 's relatively straightforward to build, and, you know, it's a it's a kind of fun phenomenology study from that point of view. So my degrees are all in meteorology and worked in a lightning research group at the national severe storms laboratory in that. I kind of got into it sideways and almost by accident as an undergrad. There was a research position available, and I got got involved in never really left. Okay. So how'd you detect lightning assuming it doesn't hit you? And it's more than five miles away. Right. It's primarily detected as with various bands in the in the radio frequency spectrum. And so depending on which part of the lightning process you want to detect you can listen for lower or higher frequencies with a radio receiver or there's even simpler versions of that simply involving digitizing charge that comes off a metal plate to the radio receiver. I have heard like more am than FM. But am radio gets really glitzy staticky in a lightning storm. Yeah. It absolutely does Lightnings very broadband emitter in the radio frequency spectrum. I was thinking when I read those FCC warnings on the back of electronics and. And because. Allowing you to listen directly to the the amplitude of the the radio signal in that band, you you can very readily pick up then the the the noise produced by lightning. And so if you wanna do lightning detection, scientifically, it's a matter of digitizing that noise fast enough to be able to resolve resolve processes, and it's a pretty high have lost the impulse. I mean, it's we look at lightning and it flashes in. It's very big here it it's a big bang. If you're close enough, so very impulsive, do you see that all across the spectrum? Yeah. It's impulsive all across the spectrum. So the the thing that you you just referred to as this. What's called the return stroke that we see it's the big bright flash of light when a lightning channel connects to the ground. So there's a whole lot of charge. That's moved over a very long distance heats up the air, and you see that bright flash of light. And the progressive sound that goes with that very impulsive heating. So there's more to it than just that lightning is not just that flash. See? Yeah. Exactly. So if you go to the very high frequency part of the electromagnetic spectrum, so tens of megahertz and above kind of right where the old analog TV channel set. At at that frequency band. The the stepping processes are on a very small scale tens to hundreds of meters in terms of step length. And so if you send some that band, you can map out the entire shape of the of the whitening channel. But that too is also an impulsive process, essentially, axes appointed mentor. Okay. Sorta understand this. I used to wear kinda assist him that would. Find gunshots by listening to audio waves. And in locate them based on time difference of arrival to the different sensors. And one of the things that was really kind of pounded into me is is. Sound moves at a certain speed. And if we are if we get the sound speed wrong because if you Minniti or whatever, then we get the location wrong, and there's a very constant proportion to it. And so what you're doing is looking at a very high frequency, which would give you a finer grain picture of what was happening is that right? Yeah. Okay. Yeah. That's right in the time. Difference of arrival is is the primary method. That's used to do to lightning detection. It's the instrument that I use mostly uses that method. And so we don't have to worry quite as much about the the propagation speed. There are some applications for that does matter, but certainly in the VHF where it's propagating through the atmosphere. It's essentially treated as a constant speed. How do you it? So is it a pretty distinct signal or are there kinds of other terrestrial interference. That can get confused. Yeah. It's so that the instrument works by very naively digitizing, the the the peak pulse. That arrives in a typically about eighty micro-second window and that and so if you have a local noise source of power line or something that's sparking on that's going to raise your local noise. Floor and reduce your your sensitivity to lightning coming off. The wall question too. My dad is to him radio. And I kind of radio in since I have a license but don't hundred. What I remember as a kid tuning in to particular band having my dad, tell me we were listening to lightning Jupiter. And I looked at this morning before the show. And if that's all true, you can do that shortwave shortwave pants, and I was wondering if it's you may not know those because it's kind of a weird thing, but that in the same region or is it somewhere else? Could we be confusing Jovian lightning lightning? That's a good question. Shortwave? So what what wavelengths is that ten to twenty five megahertz is the frequency. Yeah. It's interesting. I'm so that must somehow make it through the the ionosphere as well. So I wonder it's kind of an interesting thing that that's even possible. So yeah, that's that's close enough that I guess you could be picking it up. Louder. That's Tricia with the a lot. More impulsive. Pretty we gets here. Even though it's much bigger lightning. I'm sure. Yeah. Yeah. So that's that's interesting. Although our our our antennas are probably not that much more sensitive than a than ham radio. Probably maybe they're actually less sensitive. I'm not sure never done any ham stuff. So it's possible. You guys are picking up a a smaller signal that way. Okay. As long as we're on the topic of of blading in outerspace. Can you do do you get lightning effects from the moon? I mean do things bounce off the moon. I have never looked into that. I. Who has that? One of our listeners. Interesting. I don't injured. I don't know if that would work or not you can certainly you'll certainly get radio frequency signals that will that will propagate from the earth upward where you could detect them from a satellite. So. You know, it's it's likely that if you were you were listening on the moon you'd you'd pick that up. And so I suppose. A signal could could bounce off the moon. Again, it probably depends on if if there's is there's some other signal. That's that's known about soft. Like, there's there's I think there's. Another moon bounce stuff. That's been done. And there's a video of Milky Way in radio waves reflecting off the moon. That was fantastic. So the milky way's owned radio waves reflect off the moon. And if we point radio receivers towards the moon, we can image the Milky Way in radio spectrum, and it's just magical Erdos again ham radio operators you utilize earth moon earth for two communications. So so people do really need crazy. Yeah. Would you like to go back to ask? You you have to ask to figure out what it is that I do about. I mean, as we're giving you suggestions for papers. I wish I I wish I had the time for all the ideas out there. Okay. So you have a metal plate if I heard right and. You measure very high frequency, and then what happens? Okay. So the one that I was talking about in the very high frequency band. That's a regular DiPoto ten actually it's. Yeah. So that's that's a different thing from the the metal plate system. But we can we can talk about that metal plate. If you want. I think he wanted to hear about the whole detection system. Right. Well, actually, no, the middle points kinda cool because I I heard from someone that I could build my own lightning detection Teno with a salad bowl and a pizza pain. If you're talking to John Leman. Yeah. So so John I've actually been working on a a sort of prototype for this. And it's based on a design that really dates back to the sixties or seventies really standard atmospheric electric city instrument. I went out to my local restaurant supply store and look for a pizza plate that you might use an restaurant to serve server heat pizza and found one that fit inside the opening of a of a salad bowl. And if you hook up a charge amplifier to the to the pizza plate and digitize that you can you can detect lightning that way and salad bowl is ceramic or insulated. It's a stainless steel or bloom. They're both metal. Yeah. That's right. So the syllables really to you can think of it as giving it a nice ground plane, just a nice sort of smooth shape that isn't going to concentrate the electric field too much. And usually hang it up. Side down. So it also serves as a as a rain shield. Okay. So I have a salad bowl with the opening pointed down and a metal pizza plan. Also now, it's pointed towards the ground, but it's attached to the salad bowl through bolts glue. It's it's electrically isolated from the sale in all. Yeah. Hot glue, whatever your favorite adhesive or. Any sort of insulator that will just keep keep it separate electrically and then the electric field. In the in the atmosphere is some some background electric field. And then when charge moves around inside a thunderstorm. Let's say there's a one of those big groundstrokes and a bunch of charges moved very quickly that changes the electric field. Very quickly that induces a change in the charge on that metal plate because the electric field changed, and then the charge amplifier circuit pulls off that that charge that's been induced and that's proportional to the electric field. Jj sounds sort of like a capacitor. I mean, you have to metal bits. And then insulator between them and the new you kind of just read what the charges on this capacitor is that a reasonable mental model. That's that's not a bad bad model at all. No. I think that's good. And so what are measuring? There is pretty simple at what does my amplifier have to look like then. The audio on your question just dropped out there. What does my amplifier circuitry have to look like? It's a it's an op amp and RC circuit and a little bit of signal conditioning to reduce noise around that. But it's about the simplest circuit. You could you you could imagine. And then in ADC in a little controller, and then a little warning inside my house. It says lightning his coming. Yeah. That's right. So yeah, of course, you've got to digitize the voltage that's produced by that little little circuits ADC. And then. You know, depending on how fancy you wanna get you know, we've this version we've been testing is running at about one hundred Hertz, which is. Mine. Mind-numbingly slow. But if you get up into tens of kilohertz, you can you can resolve most of the important processes enlightening stuff. That's happening inside the cloud before a connection is made to ground and the sort of research grade sensors right now are in the sort of one to ten megahertz digitize arrange. Okay. And you said this before the the lightning struck that hits ground. That's not. That's not all of what is happening. What can you can you walk me through how lightning happens from when there's not a cloud in the sky too? When it hits the ground. Yes. Sure. So once a once, a Cumulus cloud. Starts starts to build. Gavin's fear. It gets colder as you go up. So is that cloud gets taller? You eventually start to get production of ice in the cloud. And it's collisions between precipitating ice particles called called grapple and regular smaller ice crystals that are sort of snow very small snow crystals. Those collide with one another in the presence of supercooled liquid water. And the combination of all of that is enough to allow positive and negative charge to be separated. Where the precipitating particle gets one sign of charge in the non precipitating particle gets another sign than. What what why don't why don't they stay balanced? I don't understand why they get separated. Okay. So so they can imagine them starting as neutral, and when they when they collide with one another a little bit of a little bit of the ice surface gets torn off in the process of that collision and the result of that is that one of the particles retains more of one of the signs of charge. And that's actually one of the great mysteries is exactly what's going on at that. At that is surface collision, and we have some idea from laboratory studies how to predict which sign of charge. We're going to get. But there's there's PHD level work in in refining. That that understanding someday they're gonna find out that little tiny tiny cubes are walking around in their bathrobes shuffling their feet against each other. Magic happens. I think I'm gonna teach it that way. From now a great pitcher. But interesting though is fundamentally an ice based process, right? Think about thunderstorms this summer of. Barreling across the hot southwest. But there's a lot of very complicated things happening in those thunder clouds with ice, and rain and pale and lightning. Yeah. That's exactly right. And yeah, if you can't make the ice you typically don't don't get lightening out of those storms at all. There's been some very sketchy observations of of lightning in what are called warm clouds where there's no ice phase precipitation, but those are more anecdotal reports. And so it's really a requirement to have that that deep cloud that gets into into the ice face the most why would severe thunderstorms producing a lot of hail. That's okay here in deep danger flaming. Yeah. Exactly. So the more that precipitating nice. You have the more collisions you get the more charges separated and that the consumption of that charge and reduction of the electrical stress produced by that. At charge being concentrated into regions. That are perhaps a kilometer apart. In the cloud is is what leads to lightning. So is it the ice cubes? That are falling the reposited and is keeps their staying that are negative or the other way. So there's there's actually a reversal line. That's about minus fifteen or twenty celsius in the in the cloud. And below that level. The the Garoppolo tends to charge a positive and the ice crystals charge negative and above that level, the ice crystals tend to charge positive and the grumble churches negative and in the finite. The group was the precipitating. Yep. Deadly it. Yes. So that leads then to the the basic electrical structure of thunder storm as called the normal tripolar model, it's a positive negative positive charge stacked in the vertical and between each of those. You can think of them in a simplified form is charged layers between each of those charged layers. There's a large electric field. And when the electric field reaches a certain threshold, then you can get a lightning flash to start into. This is where we get lightning to light cloud to cloud lightning yet. That's right. And yeah, where does the earth come in? I mean, why why does it go to earth? What is earth? What is crowd? It's a great place to dump a lot of charge when you have more than you more that you need to get rid of then you can neutralize using the charge. That's available inside the cloud. And so that's that's what leads to these ground strikes. Then is that it's energetically favourable and energetically favorable to move all that charge to the earth in order to neutralize the the electrical energy in the cloud. Okay. So you said energetically. Favorable favorable, which actually leads to one of the listener questions. Kaby x eight one. Go clearly a fake name not on the Bristol ticket. We've been talking about harnessing energy from lightning for a long time. And it's chaotic inside nature, but there's a lot of energy there. Why why aren't we catching lightning to charge batteries? So there's a lot of current there. But there's not a lot of energy. And so I would disagree. Yeah. It's it's a very short time process. Like, you said before it's very impulsive. So there might be an in a typical ground strike tens of killer apps for. No more than than a few milliseconds in very insert discharges. You can get something called continuing current which might last on the order of one hundred milliseconds or so, but the total amount of energy that's actually moved when you add up all that current overtime is is very very small. Okay. Let's take the question. The other way, why is anybody working in harvesting light? There are people working on that. I read about it, really. It's certainly not something I run into on a on a regular basis. And I think if you would survey the scientific community, they would say, that's that's not a a scientifically just from scientific principles of what we know about how the energy is moved around, and lightning is not a real reliably to be a successful thing. Seems we better off harvesting entire thunderstorm. Yeah. Put up a bunch of windmills. Yeah. Yeah. That's a wind solar lots. Lots more direct ways to get the get the energy out of the sun converted into electorate city. But that's the thing I've ever lasers confusion between energy and power like a very powerful event might not dissipate. A lot of energy not comprise a lot of energy because it only happens over the course of a tiny tiny tiny fraction of a second. Yeah. Exactly. Exactly. So let me can still be very damaging. So for a Winterbourne blade. In fact, there's a whole lot of charge. That's that's moved across the surface of the blade or through the interior of the blade in a in a very short amount of time. And so that leads to leads to heating just like it dozen in the air that leads to thunder in that can rupture a blade, but the the total energy is not that large. Okay. I believe that now and having gun baxley competed page, the lead me that is actually called harvesting lightning energy. The first half is all about how people are doing. It. Second half is all about how stupid that is. So clearly should have read the whole thing. Well, if you think about it people get struck by lightning, right? If it was something worth harvesting energy from would vaporize people instead of killing them to most of the time. Yeah. It's good. Yeah. Yeah. How often do you people actually struck by lightning as opposed to being near lightening strike and being and believing they were struck by lightning. Have you ever been struck bullet you or do you just believe been struck by lightning? I can definitely confirm struck by lightning though. It's been close when we were launching balloons into thunderstorms. And that's another whole funds story. But yeah, there's there's typically tens of deaths in the United States per year. And. I. I know that a large fraction of those are actually from a what's called a side flash aside splash or the terms used in the lightning safety community where there's. Sort of side part of the channel not the the main channel to ground is what what actually winds up being the person. And so the actual direct strike part of it is is relatively rare. And that's why it's a it's very dangerous to be standing under a tree. Because if you're if you're standing under a tree in that's tree get struck by lightning. There's a big potential difference between you and the tree. And so you get sort of involved in it by association. That's a good. You. Involved in a lightning strike. Are there off the shelf? Lightning detection systems that people interested in it can can purchase. There. There's certainly are devices out there that will look at things like the electric field or the look at the the size of the radio frequencies Ferrick which is going to be proportional to current. And so if you assume that a typical lightning discharge has this much current you can serve in for the the distance from that if you're in the in the back country or something I it. It's great to be informed. There's an electrified storm nearby. So that you can for instance, move to lower ground. For for a lot of folks that are, you know, going to day-to-day business, you can find variety of weather apps that you can buy a lightning ground strike detection. Maps is as part of a subscription, and that's that's fairly affordable to do. So that you can actually see exactly how far you are from the nearest nearest ground strike Heffer to the lightning strike signals travel. I mean here in California. We don't get a lot of lightning. Can I can I watch your Texas lightning with the right tenant with the right intended, you could? So there's. There's a technique that can detect the very largest ground strikes that that take place the very highest current discharges. And you can build a worldwide network to detect lightning that way with about six sensors globally. So the lightning signal gets is at the right wavelength to propagate in the earth on his fear wave guide and can make multiple trips around the earth, and from that you can you can geo locate than where that took place in the INS fears wave guide only works in certain frequencies. This goes back to what you were saying about VHF and it being broad spectrum impulse. Yeah. Exactly. Right. Yeah. So the. So those those big high current discharges. Those are moving a lot of charge over distances of kilometers. And so they have a a low frequency component. That's very large, and that can then the channel actually acts as a as an intense that does transmitting radio signal at the the right wavelength to to be caught in that that wave guide when you when you get up to the. What's called the step leader? It's the the process of lightning channel itself developing before a lot of current flows in it. That that stepping process than is a is a smaller segment of channel. So just like with an antenna, the smaller the antenna the higher frequency that? That radio frequency noises omitted at can I offer to build an antenna at my place and then find five other people to make a system. Yeah. And in fact, that's that's what we do research wise. I have some some colleagues in Alabama, for instance that. Working on a project where they they wanted to to build one of these these flat played tennis systems, and so they needed to build that network, and they designed ten or twelve of those and set them up in backyards of graduate students over a county type area, and that's enough to locate where those those processes were taking place. Is this what's known as lightning interferometry? Or is that something else? No interferometry, you have to change the change your culinary equipment there. That's usually done with a cake pan. And. Is this? How science works? Yes. Cooking is basically chemistry so close cooking Panzer, basically meteorology. Yeah. Yeah. It's a nice, well, manufactured flat cheap way to get a a shape that you need. And so instead of instead of having some custom part machine for you. You just go go shopping at your favorite local restaurant store and sea interferometry that's done with a very short baseline. Maybe a hundred meters would be a a very large spacing between the tennis. And the way you do let you interferometry is. It's a sort of an extension of the time of arrival idea, except that you're you're digitizing very very quickly like it at a one hundred eighty megahertz. The charged. It's being induced on on your cake pan. And so you do that very carefully with a very very fast digitize her and then you run that. And then you look at the interference pattern produced by the signals from each of the antennas. For the bright spot that was produced by lightning channel as that as it develops. So that essentially becomes a high speed camera view of whitening develops in the as depicted in the VHF fan. Why? Okay. This is where the details, but I'm asking meta question. Why study lightning at this level of scrutiny other than it's really damn cool. I mean, and I think that motivates a lot of us, you know, to to get interested in it is that it's basic science thing. That's that's really interesting and uses all that stuff from physics to that. You know, you you were wondering what you're gonna do with since everyone else was talking about the Newton's law and. And so yeah, I mean, we're just interested in it as a as a curiosity to start with. But if you wanna talk about understanding. Lightning safety or lightning protection. For a building. You need to know how much charge is moving. In that lightning discharge and is likely to be transferred to the building. And that allows you to then spec out a system for protecting the building. Some of the more recent applications now that we can really as computers have gotten faster. It's it's a lot of to detect lightning much more regularly and much more easily and settles us to then do continuous monitoring of lightning and that allows us to get into beceerra logical applications, so we can infer that the the storm is is intensifying because if we see more lightning we wind up seeing we can infer then the the amount of ice production in that storm is larger and that allows us to infer. The storm's updraft is stronger and all of the rest of the storm all the rest of the thunderstorm processes are really driven by the updraft in the precipitation that forms in it. So we can the US national weather service is now very very interested in understanding all of these details. Of of how lightning changes let you production changes with time as the storms storms processes of all throughout its life can lightning help you predict. When a storm is coming. Or are other methods more reliable. Yeah. It. I think that the data's gotten really quite nice now to where we can map out the the entire extent of lightning in the cloud, and even all of the branch channels and make a distinction between these you're really big extensive flashes and really tiny flashes. That are discharging tiny pockets of charge in the storm's updraft, and you can make make pictures from from lightning data that look very much like a weather radar. So you can you can certainly do storm tracking that way in fact in Francis in the western US where there's mountainous terrain. It's very difficult to locate a weather radar there in a way that will allow you to you know, comprehensively see where all the storms are. And so. No of the US weather whether agency in part of the department of commerce just launch to geostationary weather satellite. That has an optical lightning detector on it. That is is going to allow us to really serve that purpose of detecting thunderstorms comprehensively over that satellites full disk field of you. And then that will basically to answer Christopher's question. Predicting weather saves lives protects crops. The reason why we pay for it. Yeah. That's right. So, you know, your your forecast model needs to know where thunderstorms are are taking place in a in a weather forecast model and. One of the one of the applications of lightning data there for improving routine weather. Forecasts is to just that lightning. Data to say the atmosphere was overturning in this part of the the world, and that's you know, that's sort of part of the atmosphere's energy budget that we need to account for. And so you can pull that lightning data into a into a a forecast system in use that to refine the that systems depiction of the state of the atmosphere. Okay. I'm gonna go to a question from Nick exploding Lee more. What character is the lightning strike? What looks like a lightning strike, but isn't. There's more to it. But I think we should start there. When we talk about lightning strikes in and all of that. But. There are there's there's all kinds of lightning, and there's all kinds of lightning processes that happen before the strike hits the ground. Yeah. What is lightning again? We did start there. Yeah. Go all the way back. Right. So it's. It's a spark. But there's lots of different lots of different parts of that spark. And so, you know, we talked about the the lightning channel developing in those are called step leaders, and as those stepped leaders develop even before they make a connection with the ground. And this is how the the in cloud flashes work all the time. You know, once you have a channel network that's developed sufficiently. It's kind of a double ended tree structure and charged can move back and forth between one end of the tree or another to rebalance how the charges configured and minimize the the energy imbalance. And so. Any sort of larger charged flow along that channel network is going to light up the cloud. And you would you would see the see the cloud light up. We would we would call that lightning. And sometimes you can even hear thunder from that. And then, you know, as that channel sometimes we'll step down towards ground in a way when it makes that connection than you get these ground strikes, and that's another another part of the lightning process that we would characterize. I've heard. From pop science occasionally that oh lightning doesn't go from the cloud to the ground. It goes from the crowd to cloud. Does that have any meaning at all or? Yeah. So that's that's a super fascinating. Super fascinating story in. In terms of scientific communication. So. When you have. Almost all all ground strikes UC start by channel. That's that's developed somewhere in the cloud in its stepping down towards the ground. And when that channel connects to the ground, then there's a potential wave that that develops from the ground and goes back up into the cloud. And that's what results in the heating and funder, and what you would sort of consider the the human sensible phenomenon that societas with a with a ground strike, but. You know, there was when that study was was done. I believe it was sometime in the ninety s that have demonstrated that there was this this potential wave that propagated back upward. Once that connection was made. That got sort of picked up by the by media and described as lightning goes from the ground up to the cloud. But that left out the entire part of the story where lightning channel developed to make the connection with ground in the first place. I'm gonna make that my ringtone what he just said. And then I'm going to have another one that says well, actually. I asked for. It was great because we do get pop science. Pick something hooky try to often the the real science gets lost in the oh, did you know that what you think is really this is that back to the cake pan interferometry? Where they never thought. I'd say together. One hundred meters apart. That's not very far when you're talking about light or high frequence. I mean, it's far for high frequency signal. It just doesn't seem very far apart. If you're doing time defensive arrival sort of things, right? And for a time difference of arrival, you want twenty kilometers or or something like that to really. To make that work the easiest. But when you're when you're doing that hundred meters spacing that's gonna be, you know, you're you're focused on individual on a lining individuals sort of fluctuations within a continuous signal. That's fluctuating, you know, some tens of megahertz. And so there you you don't want as much time difference between between those those peaks or because you're digitizing so fast. You don't need as much separation in order to distinguish distinguished processes from one another. In fact, it works against too timid to sense within affirmat-, you wanna have a few multiples of wavelength which hundred meters sounds about right? Yeah. Yeah. Exactly. And if you're trying to do interferometry, and you had a storm on two sides not that you're in the middle of storm. But you had one. Storm off to the left months after the Ray. Would it just give you garbage data? No, you would. So the the way the data is often displayed is it's a you can imagine a hemispheric dome above the above the interferometer and the nets projected down onto a flat plane. And so if you had something happening to the left of you and the right of you, you you would see processes. That are happening simultaneously. It's easier. If there's only one source that's emitting at a time. But if you actually look at techniques from radio astronomy, and they they have methods for doing multiple multiple source detection at the same time. So for a for letting discharge typical lightning discharge really you've intend to see the that lightning discharge cover the entire sort of hemispheric field view of the Frometa from right to left. Yeah. Or just sort of spatially covering it sort of as Mattel of Asian. Field of you. Yeah. You don't want it to saturate, you know, in terms of amplitude now, it's burn things. Yeah. Or or just you avoid being able to cross correlate the peaks and the the fluctuations. And to cross correlate is is one of the things. I was hoping you would say because in order to find things. In time from different directions, usually the cross correlation shows you which direction you're coming from is kinda right? Let's see. That's not how I I'm familiar with processing. The time of arrival stuff that I normally work with. But you can you can certainly frame it as a as a cross correlation. Let me be question. The correct way. What kind of signal processing do do you under data? Oh, yeah. So time difference of arrival processing with the non interferometer data is done with a lumber Marquardt algorithm. It's the it's a non linear least squares retrieval, given a bundle of time of arrivals that, you know, come from the same point, and a a sort of test solution that you iterative Lee refined to match the observed arrival times and so. It's a. When it comes down to it. It's at least wears retrieval problem. And then you also have the trouble of matching up, which lightning pulses are which detected pulses go together. And we we get around that computers are fast enough that you can kind of get around that in a brute force way without even being too smart about it. And just checking all the all the combinations. What about the impulse detection? Do you have special techniques for that? Or is it just before it was quiet, and now it's loud. Yes. So there's a an instrument that was the instrument that I use regularly was invented the New Mexico tech in the late nineteen nineties and it combines of radio receiver. That's digitizing that AM noise. We talked about earlier it does that very fast at about twenty five megahertz and every eighty microseconds it records, the time of the peak peak pulse that that. That arrived at the antenna in that eighty second window, and so what allowed that instrument to work. Well is the ability to combine ah digitize which has been around for a while with a with a GPS timing reference. That's precise enough to allow us to work on a on lightning time-scales. And so others, you know, some custom electron IX that that do the the peak detection within that eighty microseconds window, and then that gets there that gets sent along with the GPS time into a little Lennox, computer. That is is that every every site in writes, the data to a hard drive using a very sort of conventional approach from there. Another are connected by the internet, and we get the get the data back, and we can actually watch this in real time. So this is really fun when I have a thunderstorm here in in west, Texas. There's a a server I have that collects data from each of the stations streamed in real time, and that least squares retrieval process. We just talked about is runs fast enough that we can watch on a display. While like to describe this. As like, you you see a lightning flash happen outside. It'll show up on the display with its branch channel structure, and then you hear the thunder from it. That'd be kind of fun Saturday afternoon. It really is. Yeah. It's. You can sort of play a game. Like is. Is that loud one? I just heard that really large lightning flash will. Yeah. There it is. And so it's fun fun. Find find the flash game. This gears for second ball late ni which brought up in lightning round. But Nick has an question about it kind of same as mine is is it real? And what is it? And I guess the real question. I have is if it is real what is it? I I don't think we know. That's it's one of those where we have one of those phenomenon where we have. Reliable reports of it that date back hundreds of years, and yet it's rare enough that we can't really design an experiment to go to observe it in a sort of scientifically organized sort of way, there's been attempts in laboratories to. Send a bunch of current through things like silicon plates or other materials that lead to these these sort of stable plasmas that kinda roll along the floor. And so you can produce some things in light in laboratory settings that behave a bit like ball lightning. But precisely what is going on there that that leads to the, you know, the the full scale phenomena that we observe in in the atmosphere is not real clear. I'm not even sure we could. We could say definitively exactly what scale it is about. You. You hear reports of for instance, the ball lightning moving through a a a window or. You know? So it's maybe maybe about that size. They're just ghosts. Could be could be ghosts. Go with the love of physics. But there are weird lightning phenomena beyond normal lightning. That have been reliably observed such as the things at the top of thunder clouds that have been photographed from space station. Yeah. Yeah. That's right. Yeah. There's sprites in blue jets and elves and halos this whole. This whole collection of creatively named things. So sprite take place when you have a whole lot of charge moved around in a regular a regular thunderstorm discharged, one of these very largest discharges. And that moves so much charge that the electric field in the INS fear changes enough that the I honest fear breaks down you get a secondary lightning discharge in the atmosphere. And so that's what sprite is. To lightning. It goes up. It's not it's not even connected. The sprites aren't even connected to the regular thunderstorm except except through the field aloft changing because the thunder storm changed. The other things like us like blue jets gigantic jets. Those are lightning discharges that go up. And you can think of those. As like a like a ground strike except thing that's being struck as the INS fear. Is the sphere grounded? A media why it's a differently charged region. Yeah. I guess so. You don't think about that? Because you're like, oh, well, it hits grown in ground is important because it's. Yeah. And so as cloud Diana's feeling all right. I sorta by it. But I think you might be making it up. I could be I could be next time when age returns that the American geophysical union has its annual meeting every year in San Francisco, and you should come hang out with all the lightning people. There's a set of sessions there every year, and San Francisco, you definitely want us third a heckle, absolutely, absolutely. One of the things that got me interested in lightning, and how formed was this book called the cloud spotters guide. Are you familiar with? I have I have seen it do. I have. I'm looking behind me on my bookshelf care. I it's by Gavin Pretoria. Piney penny. Luckily, he doesn't listen to the show. So I can totally butchers name. I don't think I see. I don't think I see a copy of it. But I've definitely heard of it. Yeah. One of the stories it had in that book. And in another book that was similar was of a pilot in who who jetted from his plane after hitting storm unexpectedly and was in his pilot chair his military pilot so jet Chan, and he fell and the updraft kept lifting him up. And then he would keep falling in going up and back and forth for forty minutes as plausible that have you dream. No doubt. I've heard this story. Yeah. And it's I tend to believe pilots when when they've they've gone through something like that. That I would consider that as as reliable of allay report is you could you could get and. I don't I don't know the case in a great amount of detail. But the idea that someone could be carried up and down through a thunderstorm for that amount of time yet it that it's not implausible, and certainly sounds miserable. You don't wanna try it? No, no. Kinda miserable. Because I guess he almost drowned at one point, and he broke some pieces also very cold. Yeah. Frostbite too. But if you were prepared wooden zone like fun. No. Sounds sounds dangerous there there is. There was actually a storm penetrating aircraft. That was an old t twenty eight piston engined plane that was that had had all of its leading edges on the wings and things up armored. And so they would fly that threw up to. I think one inch hail and fly right through the updraft in a storm. One of one of the pilots that now is a. Is also still an active scientist and does a bunch of work and high-speed lightning photography in videography, which is useful for studying lightning physics. So that. There is actually ways to to get inside the funder storm that aircraft has since been decommissioned, and there's been talk of bringing in a ten aircraft into service offer that role, but the budgets being what they are. It's may be tricky to get that project completed. You can have to start telling people important. It is to study lightning it how it will save lives and stop telling them you're doing 'cause it's so damn cool. Yeah. Yeah. You know, it the ability to measure inside a thunderstorm is so important because because you can do some things with remote sensing with radars. But there's nothing like a like an institute verification where you can actually look at the population of of ice crystals in Garoppolo and supercooled water, and you know, really figure that out that's turns out to have importance for climate studies as well, even where if you wanna know how much of the clouds are big component of the earth's radiative energy budget. And so if you want to understand climate change, you need to understand how clouds are comprised, and and exactly how long wave shortwave radiation is going to interact with those clouds as part of the climate system. Supercooled water a few times and supercooled water is water. There's cold enough to freeze, but it can't because water kind of needs a catalyst to freeze where a catalyst is less of a chemical here. More of dust particle or a little tiny molecule it can on to. And then it starts building. It's crystal but supercooled water won't crystallize on its own. All right. Yeah. You got you got that. Exactly. Right. That's until the. A water droplet? That's pure water gets down to about minus thirty eight to minus forty celsius. It's it'll remain in liquid form. And then once it gets that cold in in colder, it'll homogeneous Lee freeze. And so it's important that we keep atmosphere. Very dirty. So that we get lots of our clouds back. I wouldn't exactly advocate that I would. You could ask folks that lived in lived in London at the you know, during the start of the industrial revolution. If they if they enjoyed the atmosphere being kept at led to a lot of fog, but we're doing. Yeah. Can't see the tree across the street. So that oh you've got. Yeah. The big wildfires. We're not anywhere near them. But we are getting smoke. Feel a lot more for the people who are actually near them. Yeah. Yes. Those are some some scary fires and real real tragic situation there. Has gone back to discussing fun things further awhile. And so one of the things I wanted to ask you about was this weather balloon thing you go out in the middle of storm with the weather balloon soom. There's a key attached to it like like reenactments, Ben Franklin's thing. Yeah. It's it's it's Ben Franklin, but we let go and that allows us to keep doing this university setting. The this. This. Yeah. These are these are big balloons that we we launched into thunderstorms. And this was my undergraduate and graduate research in in Oklahoma, Dave rust who passed away a couple years ago was the the sort of leader of this effort to do atmospheric electric city ballooning in Oklahoma along with with Don Mogoma and. And yeah, these are these are big balloons there about twenty feet long when we launched them other. Usually, we would watch polyethylene balloons. It's very thin polyethylene, basically a large garbage bag. That that we inflate with helium, and it's gets launched out of a out of a launch to we inflate it in the back of a U-Haul truck and chase. Chase storms of the U haul truck which is its own interesting experience. Why are you renting our truck today? Yup. And then then there would be the service. Call like, no seriously. We really do need tires on this. We're not just moving to bed today. And yeah, we'd have we we we chased with that and a couple of other vehicles for data collection. And so yeah, watch this big balloon into into a cloud. It has a what's called a radio saw Donnette which measures pressure temperature and humidity. Gives us position information is the balloon flies to the cloud. And then at the very very tail end of the train of instruments hanging off the balloon is an electric field meter that we use to measure, the the vector electric field inside the cloud and by electric field meter, you mean, basically a metal marble. It's it's to marbles attached to a to a spinning rod in those marbles are made of aluminum and just like our our flat plate. Lightning in those metal spheres are attached to a charge amplifier circuit. And as those spheres, spin in the thunderstorms electric field charges induced on those fears back and forth and the charge amplifier digitises that the that signal and that gives us a measurement than that's proportional to the electric field on the cloud. Is it try to radio this to you or do you collect the whole apparatus afterwards? It does both. So the the original version of the instrument actually sized those those spinning spheres so that they were the right size to radiate in the four hundred megahertz radio band. That's used for meteorological instruments that since been reengineer to put a proper transmitter separate from the spinning spheres. So we we collect the data in real time. That way. And then. The date is also recorded on board, and that's perfectly clean signal of its recorded. Doesn't have any transmission noise and things in it. So we also try and retrieve those those instruments that way sue the the two spinning ball. Amine. Do they don't go at a constant rate because they're being essentially pushed around by the electric field of the storm that right? No, they're they're driven by a motor. So they k- they do spend it a constant rate. And that that helps us as a in doing the signal processing because we can also then record the record a reference for the spin rate and then use that to it's called D modulate, the the the electric field signal that's recorded invitee modulate. That is every time. It was in in circle. It gets a different view of the world into kind of forms a sine wave. If you had if you charge them one side, and none on the other it would be high low the getting lower lower lower low and then back to be going around in a circle. And so your data would sign wave on one channel and on the other Chennault it would like look like a sine wave that was exactly one eighty off. Yeah. Exactly. And so you've described that perfectly. It's. And then we record another sign wave from an accelerometer that's inside this fears that tells us the position of this fears, but we do that as a as a D modulating problem where we multiply the reference sine wave with the electric field sine wave and. And use that to. And then do some filtering to pull out the the very electric field. And so the remedy is because you might not be in a single plane. You're not spending on a desk, you're in three D space and exceleron. Honorable tell you the tilt. So the accelerometer the accelerometer is actually how we get the in phase and ninety degrees out of phase orientation of this fear. Yeah. One hundred eighty would just cancel us a lot. But so the we have a zero ninety degree reference from the accelerometer is that gives us the the position of this fears. They are spinning in a in a plane, and then the whole instrument platform also has that also rotates usually around vertical access there's paddles on the end of that spinning rod that has the the spheres attached to it. And that spinning the dynamic forces on those pedals caused the instrument to rotate around at a slower rate than our spin rate. And so that's what allows us to get the vector electric field out of the charge induced on this fears is it spins around, and the NFL activist is you are taking a picture of the electricity in the whole cloud in you end up with Chile cooking, strictures or more general pictures. It gives you a gives you the. Yeah. The the electric field variability in the cloud. You can use ghosts law from our beloved physics class too. In for charged density from how the electric field varies with height. And so that's how we know the an in Vero FAI what we think the charge structure is in thunderstorms that normal try poll, plus minus plus structure is something that you see in the fluctuations of the electric field. And then the other thing it tells us is the maximum electric field that we we observe in clouds and that maximum electric field is is much much less than the actual breakdown dialectic strength of the atmosphere. And so that's another one of the enduring mysteries in lightning that we know roughly at what electric field lightning starts at. And but it it's not just a conventional dialectic breakdown that allows the lightning flash to get started. And so there's some high energy physics explanations for for what might be going on there. Relativistic things even really. Yeah. Start the show for another hour where we talk about tell us about relativity and lightning. Yeah. So now, we're this is where it would be great. If I didn't have meteorology back six one. But. What? For my colleagues over the year. You you do observe x rays and gamma rays that are omitted by by lightning flashes. These are actually a source of noise for astronomers that are trying to do. Satellite-based detection of gamma Ray bursts from from Estra nominal sources. And that is that has something to do with probably the initial breakdown stage of the lightning discharge in. It's a. There's there's electrons that are accelerated in the electric field up to relativistic speeds and that results then in these these higher energy. Emissions that are due relativistic processes cool. Did you get all that? Can you? Explain it to me later. Okay. Who? Lightning thunderstorms are particle accelerators. All right. Yeah. That that's cool. That's that's that's excellent. Yeah. Is there such a thing as lightning tourism? Money tour never seen lightning with a Samsonite. Covers a lot of miles. I mean. And does so with low carbon emissions. So that's that's a plus. The. I there are certainly a storm chasing tours that you can get a lot of those are based around trying to trying to find a tornado and see some storms structure. There's folks that also do that from Amora photographic point of view where you want to be a little bit further away from the storm and get some good photos of it. Lightnings of part of that. And you could certainly I'm sure there's there's good lightning photographs that are taken as part of those things as some other kind of tourism. You've you've heard of no I just wanted to know where I could go to see lightning. Yeah. Christopher last time. There was a storm here, and there's lightning Chris from become inside right away. It was very sad. That's. Action. That's probably safe move you. So the Raya rare California thunderstorm. It was it's kind of a neat story when the geostationary lightning map on the on the Noah satellite was was launched. It was built by a the instrument itself was built by a team in Palo Alto Lockheed Martin. And they as they were doing that is they were doing the initial instrument checkout. There happened to be thunderstorm over California on the day when they were doing some of those initial checkout. So they actually got the the rear local lightning event right over where the red overhead where the instrument was developed. That is pretty rare. Recall in the case, you're talking about we were at the beach and lightning striking the water. Gotten out of the water. From indrek. He says there isn't Estonia proverb that goes lightning keep striking the same house. This is opposite to the English. Speakers lightning never strikes the same place twice, which one is more true. Oh boy. Fascinating. How these how science and culture sort of interact or physics in culture interactive to give these different impressions of things. So I wonder if that house that keeps getting struck is a, you know, if it were sitting on top of a hill, it would behave just like toll TV towers radio towers that tend to wind up concentrating any lightning strikes in the vicinity to the location of those towers and so. So so perhaps it's a it's a house in an unlucky location that. That winds up getting struck. But overall, I would say lightning. I'd I would say is a fairly random process. And if there's nothing else to drive at any given direction, it's it's gonna it's gonna move around pretty randomly. Okay. So great answer that was. Odd. But interesting question, I have one more question for you before we let you go about your weekend. This one is from Stony monster. What powers will I develop if I get struck? Could you be specific specific? And what is the best way to get struck in order to get these powers? I highly do not recommend that. So the the new. But there are there are major sort of if you survive a lightning strike, and you know, people do. There are persistent neurological affects that include X men. Not not extant powers. Unfortunately. No. It's it's I shouldn't make fun. It is pretty bad. I mean. Yeah. That's it really does leave people with debilitating injuries or depression or other things that, you know, really as a significant impact on their quality of life, and there's even sort of sort of things that the death statistics don't capture in terms of the impact of lightning on, folks. So even we've done a good job of reducing lightning deaths. Those injuries can still be really quite severe. All right. I'm chasing. Lightning lightning. Well, Eric thank you for being with us. Do you have any thoughts? He'd like to leave us with. I would I would say that you know, if if any of this sounds interesting to you it would. Take as much math and physics is as you can if you're a say, a college student listening, and we. We always love having people that have an interest in instruments and building hardware, you know, that that enlist in a. In graduate programs to study, this kind of thing and the the ability to make things and build instruments is just such a. Such an advantage in maybe a a skill. That's a little bit too rare. So you know, if there's a if you have that kind of interest. I'd I'd encourage you to go for it. Cool. Well, our guest has been air Bruening, professor of atmospheric science at Texas Tech university. Thank you again for being with us ERC. You're welcome. I really enjoyed talking. Thank you very much to our patriots scrubbers both for Eric's, Mike, and they're awesome questions, including Nick, Tom Anderson, and Indrek and k b x eighty one, and I guess Doni muster though, I feel a little weird because he's gonna get thanked again special. Thanks to John Leman of the don't panic GIO cast for connecting us to Eric. And for KENNY'S Amore questions. I didn't have to hardly any work this week Eric's episode on the GIO cast was a lot of fun to listen to finally thank you to Stony Christopher for producing cozine. And thank you for listening. You can always contact us at show it embedded FM or hit the context link on metadata FM. Now, a quote to leave you with this is. Is from Bob Ross in painting. You have unlimited power have the ability to move mountains. You could bend rivers. I wanna get home. The only thing I have power over is the garbage. Emitted is an independently produced radio show that focuses on the many aspects of engineering. It is a production of logical elegance and embedded software consulting company in California. If there are advertisements in the show. We did not put them there and do not receive money from them at this time. Our sponsors are logical elegance and listeners like you.

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