UNH Today

It was pure serendipity that Joe Dwyer became the world expert in the high-energy physics behind lightning strikes, and ironic that he's now landed back in the virtual stomping grounds of his research from days of yore.

Dwyer, who came from the Florida Institute of Technology to the UNH Space Science Center last September as the new Peter T. Paul Chair in Space Sciences, began his career doing space instrumentation work — one of the core strengths and legacies of the SSC. But in 2001, as a young assistant professor at FIT, he abruptly switched gears while applying for a National Science Foundation Faculty Early Career Development (CAREER) grant.

Funded at the time by NASA for his space physics research, Dwyer was encouraged to find some other line of work for his CAREER proposal, since it was unlikely the NSF would provide him with five years of funding to continue his NASA research.

"I needed to find something else to do and, meanwhile, there was all this 'boom, boom, boom' going on outside my window. There’s a lot of lightning in Florida,” Dwyer recalls. “So I started wondering if maybe I could do something with that."

He had heard about lightning possibly producing x-rays — something that had been talked about since the 1920s. "People had been trying to see if it was indeed true for more than 70 years, but at that time researchers still didn’t know the answer," Dwyer says. "People occasionally reported detecting x-rays from lightning, but nobody had ever confirmed it."

Joe Dwyer had found his CAREER grant research focus.

"That’s where things were back in 2001. Few scientists really believed lightning emitted x-rays, but because it was an idea that never quite died I thought, 'OK, I know how to build x-ray detectors. I’ll just set them up outside and perhaps we can settle this once and for all,'" Dwyer says.

It was a bold stance for a young researcher to take when, admittedly, he didn't know the first thing about his topic of choice.

"Most people with a modest interest in the subject probably knew more about lightning than I did at the time. I figured there must be someone in Florida who knows about lightning and could help."

So he did a web search on "lightning expert in Florida" and came up with a fellow named Martin Uman — a world expert in lightning.

"I sent him an email telling him what I was proposing to do — to see if lightning emitted x-rays — and asked if he might help. To show you how little I knew at the time, I even misspelled lightning in that email," Dwyer says with grin.

"Despite that blunder Martin Uman wrote back anyway and said that we could actually use triggered lightning to study this so you don’t have to sit around waiting for years until natural lightning strikes near your instrument. You can make it on demand, or at least give it a place to strike, by setting up by a rocket launcher and launching a rocket tethered to the ground by a copper coil, which can trigger a lightning strike," explains Dwyer. "So I put that in the proposal."

In the meantime, there he was in Florida — the Land of Lightning, he had some start-up money he could use and graduate students who could help, and he'd had experience with x-ray instrumentation years before while at Columbia University as a research scientist. Why await word from the NSF on his CAREER proposal?

Moreover, sensing that his proposal was a long shot at best since he'd never done any research in the field and never published a single lightning research paper, Dwyer and colleagues just dove right in. They built an instrument that could accurately measure x-rays from lightning at the ground, successfully triggered a lightning strike via a tethered rocket and, after pulling the trigger many times, showed once and for all that lightning does indeed emit x-rays.

"Lots and lots of x-rays, and the signals were really big," notes Dwyer. He adds, "Actually, in hindsight, several people probably had measured the x-rays before, but my group did the careful, detailed measurements and repeated the experiment over and over with precision, which you can do with triggered lightning. We published in Science and with that it was finally established that lightning emits x-rays."

Meanwhile, Dwyer found out that he had actually won the CAREER award.

"Within a few months of getting the CAREER award I’d done most of the things that I said I’d do in that five-year period," Dwyer says. "So the pressure was off and I was able to take some chances in this same field. It turns out there was a lot of low-hanging fruit on this subject and we were able to make many important discoveries about lightning." All of which made him the go-to guy for lightning.

He adds, "Surprisingly, the field is going through this growth phase right now where a lot of really important lightning discoveries are being made all the time, which for scientists is really exciting."

Ben Franklin aside, lightning remains a deep mystery

It turns out the x-ray mystery that Dwyer helped solve once and for all just scratched the surface of lightning-related mysteries remaining to be probed. In fact, Dwyer notes, "Lightning is an unsolved problem in science, we really don’t know how it works at the basic level. In physics we’re usually answering 'how' questions, and with respect to lightning these are: 'How does it get started?' — or what’s known as the initiation problem; and, 'How does it move?' — or the propagation problem."

"And I’d say the initiation problem has to be one of the biggest mysteries in the atmospheric sciences — how you get lightning started inside a thunderstorm. It’s hard to know how to even approach the problem."

How could something so common — lightning discharges occur about four million times per day and lightning strikes cause more deaths and injuries in the U.S. than either hurricanes or tornados — remain so poorly understood?

"It’s an overlooked area of research for one thing," says Dwyer. "I think a lot of people assume it’s a solved problem. Everyone knows Ben Franklin 'solved' it 250 years ago, but he simply showed lightning was an electrical phenomena, which was important, but that certainly didn’t solve the problem."

Even today, scientists understand the inside of a star halfway across the universe better than how lightning gets started inside a thunderstorm five miles above our heads. And, Dwyer notes, lightning actually shouldn't be occurring according to what little is known about the inner workings of thunderstorms.

"You look at how thunderstorms charge up and the electric fields never seem to be large enough to actually make a spark, and yet we see lightning coming out four million times per day. Then, it can travel hundreds of miles through the clouds, all the way across a state sometimes, but we don’t really understand how it does that either."

Perhaps x-ray marks the spot.

Another reason why lightning is an overlooked area of physics is that it’s a very tough phenomenon to research. As Dwyer notes, a thunderstorm is a big dangerous place; you can’t see inside it with a telescope, it’s hard to get into, and if you do fly inside it with an airplane you might not have an airplane coming out. "It can ice up, turbulence can rip it apart, lightning can strike, there are a half dozen ways you can get killed in an airplane in a thunderstorm."

With all that for context, it's clear to see how nailing down the x-ray/lightning connection might open wide a new avenue of exploration as to the how and why of lightning.

Of the x-ray finding Dwyer says, "We finally nailed down something really new and different about lightning and suddenly we’ve got a clue as to how lightning might get started and how it moves."

Related to the x-rays emitted by lightning is a phenomena known as terrestrial gamma-ray flashes, or TGFs, that can be seen from outer space. These fleeting, monster bursts of gamma rays, originally thought to originate at high altitudes, were finally shown to come out of thunderstorms. So bright are they that they can temporarily blind spacecraft in low-Earth orbit-spacecraft designed to measure gamma rays from all over the universe but that are unable to keep up with the gamma-ray count rates coming from thunderstorms.

"These gamma rays are emitted from thunderstorms around the time lightning is initiating, so these TGFs are right there in the mix and we can use them as another probe into the processes. The gamma rays coming out of thunderstorms are probably a souped-up version of the x-rays we see on the ground from lightning."

But it is only speculation that x-rays and TGFs are important for lightning initiation. If these processes were taken out of the picture would lightning initiation cease?

"We don’t know, but at the very least it could be an interesting side effect, and in that case it would help us further probe what’s going on. So, at a minimum, these processes will provide us with a useful investigative tool, while on the other hand they might prove to be the keys to the kingdom of lightning initiation and propagation."

While actively continuing his triggered lightning research in Florida, back in the world of space instrumentation and mathematical modeling at the SSC, Dwyer is comparing models with data from instruments on the Fermi Gamma-Ray Space Telescope and the Reuven Ramaty High Energy Solar Spectroscopic Imager spacecraft, which have instruments that can measure gamma rays coming from thunderstorms. He also does pencil and paper theoretical work and runs computer simulations.

Says Dwyer, "This is a field of research that’s still new enough where someone like me can do experimental and theoretical work at the same time, whereas in a more mature field, such as space physics, it would be difficult to do both — you usually have to pick one or the other to be good at it."