Shocking developments in lightning research
Despite how often lightning flashes, humans still know little about it. But at New Mexico Tech’s Langmuir Laboratory for Atmospheric Research several miles out of town, scientists are researching lightning and discovering many things.
A charge jumping from point to point is well-understood and can easily be replicated in the laboratory or in the home. The little jolt that comes when you rub your socks on a carpet, then touch something metal, is the same phenomenon that occurs with lightning. These both build up an electric field.
An electric field is similar to water in a pipe at pressure. When there is too strong a field in one place, the charge — like water — bursts and moves to somewhere with a weaker field, like when a water pipe bursts.
However, according to NMT Associate Physics Professor Dr. Ken Eack, sparks in the lab only occur when there is a very powerful electric field, over a million volts per meter. Dr. Joseph Dwyer, of the Florida Institute of Technology, estimated the minimum amount field strength required for a spark through air at about three million volts per meter.
But in the many decades people have been studying and measuring storms, rarely do they find a storm with even a few hundred thousand volts per meter. The question that has so plagued atmospheric physics is how a spark can form at less than a 10th of the expected threshold.
There are a few popular theories on why lightning flashes can occur. The simplest is that there are small regions with very powerful electric fields inside clouds that decades of measurement simply haven’t found.
Another theory suggests ice crystals in clouds cause small, strong electric fields. Near the point of a crystal, the electric field gets stronger.
But there’s another fundamental question about lightning to which there is still no satisfactory answer. In a storm that is soon to produce lightning, positive and negative charges are not mingled. There is a small region of positive charge at the bottom of the cloud, a large region of negative charge above that and a large region of positive charge at the top. When water freezes, it picks up a charge. Larger hail particles gather negative charges, while smaller ice crystals gather a positive charge. Why these gather positive versus negative charges is not well understood.
There are hypotheses and theories for these and many other questions, but more testing and new data is necessary to refine or affirm these theories. That is where The Langmuir lab comes in.
Built in 1963, the Langmuir Laboratory for Atmospheric Research is a facility dedicated to studying lightning. It stands near South Baldy Peak alongside the Magdalena Ridge Observatory.
These facilities have produced some very interesting results in their decades standing. For instance, they disproved one of Benjamin Franklin’s theories and revolutionized the lightning rod.
Franklin theorized lightning could be drawn to a pointed lightning rod by virtue of its being pointy, and given other strike points of similar height, lightning would strike a pointed object preferentially. Though humans have learned a lot about electricity in the years since, pointed lightning rods were still the accepted design.
However, in the 80s and 90s, Langmuir physicists tested a blunt lightning rod and a pointed lightning rod side-by-side, as a controlled test hadn’t really been done before, according to NMT Physicist Dr. Graydon Aulich. In the years they were up, 13 flashes hit the blunt rod while none hit the pointed rod. The results were published at the turn of the 21st century, and blunt lightning rods have grown more popular worldwide, said Aulich.
Though Aulich is still testing lightning rods, it’s a minor point of study. This year’s main focus is triggered lightning.
When a long wire is attached to a rocket launched into a storm, lightning will strike the rocket. Lightning tends to strike taller things, so sending a rocket with a grounded wire above everything nearby makes a good target for a flash. Lightning flashes are difficult to predict, which makes them even more difficult to study, so triggering a flash that will come to a specific point is very useful.
The man in charge of the system as it stands is one Jake Trueblood. Trueblood is a graduate student at NMT, seeking his master’s in physics instrumentation. This marks his third summer up in the lab, and this summer is particularly special.
“This is our first summer with current-measuring facilities,” said Trueblood. Last summer, he redesigned the triggered lightning system to include a component that would measure the electrical current of a lightning strike.
“We didn’t know how it would work, but when we tried it, (the system) worked awesomely,” Trueblood said with all the swagger due a man who can call down lightning.
He will graduate in either December or May, having planned to his thesis on his work at Langmuir. Specifically, he plans to look at the current data he’s gathering and look at the differences between natural lightning and triggered lightning.
Still, triggering a flash of lightning is not as simple as pressing a button — or blowing into a tube. Trueblood describes a wire fed into a faraday cage as a good way to lose a hand during a lightning storm. If a conductor passes into a faraday cage, it would just guide charge into the cage, which defeats the purpose.
Electricity will follow a path of least resistance. Metal provides less resistance than air or living things, so putting a person into a big enough grounded metal container can make them safe from lightning, even if it strikes the container directly. The electricity passes through the container, around the person and into the ground. That container is called a faraday cage.
Trueblood tries to time his rocket launches as close as possible to when lightning would strike naturally. His launches are guided by information from the series of sensors in the kivas — underground faraday cages at the launch site — and around the lab. This brings his successful trigger rate to around 50 percent. It also makes his triggered strikes more similar to natural lightning.
North of the kivas, past the Magdalena Ridge Observatory, is the balloon hangar, where Dr. Eack and NMT Physics Professor Dr. William P. Winn, Langmuir Lab chairman, do much of their work. The equipment near the hangar is used to measure various elements of a storm, such as the strength of the electric field. Inside the hangar, they prepare strings of lab equipment to be suspended from a weather balloon and sent in to the center of a storm. A typical string of equipment includes a parachute and heating element, which triggers at a certain altitude, cuts the line holding the string to the weather balloon and allows the string to land more slowly; an x-ray sensor — part of Eack’s work; a spot, which produces a signal so the string can be found more easily; and an esonde — a device developed by Winn and fellow NMT Physics Professor Dr. Richard Sonnenfeld.
An esonde is based on an older piece of storm studying equipment called a radiosonde. A radiosonde is a radio circuit attached to devices to measure temperature, pressure and humidity, which then transmits data back to the laboratory via radio waves. An esonde measures how electric fields in a storm are affected by lightning. The root word, sonde, is French and translates to sound. In this case, sounding is a nautical term — ships sound in order to figure out the temperature of the water they are in.
Eack’s part of the weather balloon string is interesting, as well, and related to a relatively new topic of study. Lightning produces high-frequency electromagnetic radiation — such as x-rays — when it flashes, and such radiation is also emitted from powerful storms. Eack’s current goal is to find out why and how this happens and whether or not this radiation has anything to do with how lightning is initiated.
What Eack proposes is similar in effect to an avalanche. When an avalanche occurs, a large enough chunk of snow falls a few feet down a hill, causing more snow to fall, which in turn causes more and more to fall. Eventually, the amount of snow moving down the hill is huge. Eack proposes that a few electrons moving nearly the speed of light hit the air molecules around them, knocking electrons free, causing an avalanche of charge. This allows lightning to flash with a weaker electric field. Research has already determined that electrons only move a few meters in a lightning bolt, said Trueblood, and that it’s the charge that moves a long distance. Eack’s research may show how it begins.
At the north end of the facility is the main building and dormitories, where researchers eat and sleep during extended stays at the facility. On the third floor, positioned well away from the kivas, is where post-doctorate Harald Edens runs the high-speed camera, among other things. This camera takes huge numbers of exposures per second in order to capture an entire flash of lightning. When Edens hits the button right after a flash, the camera stores the last second of footage.
He works with Dr. Aulich, using the 20-antenna Lightning Mapping Array in the surrounding area to get accurate three-dimensional maps of lightning strikes. According to Trueblood, it takes data from at least six antennas to get an accurate map of a lightning bolt.
There is another antenna array surrounding the mountain: the Langmuir Electric Field Array. This is Dr. Sonnenfeld’s focus. This array consists of nine antennas and measures changes in electric fields caused by lightning, similar to an esonde. The array can operate 24 hours a day, allowing it to observes storms at all hours. Its measurements can be combined with those of the LMA to show how charges move in and around lightning.
It can also reveal continuing currents, which are related to longer-lasting flashes of lightning. While some flashes occur in thousandths of seconds, others last much longer. Such flashes are responsible for most fires caused by lightning. Data from the LEFA and the LMA could help reveal why and how longer-lasting flashes occur.
Though all of these projects operate independently, each measurement contributes to more than one project. This collaborative research is part of what makes the lab special.
“The biggest strength of Langmuir Lab is that it allows multiple Tech faculty and faculty from other universities to work together and measure lightning in several ways at the same time, learning together more than we could learn separately,” said Sonnenfeld. “The scientists bring their own interest and expertise to the research, but they share data, and the resulting collaboration makes the Langmuir group the strongest lightning research group in the world.”
All of these people and more work with the lab’s resources high in the mountains in order to study a common but ill-understood phenomenon, dedicated to the expansion of human knowledge.