Traveling Back in Time to Investigate Aurora Mysteries
With space being increasingly talked about in the same breath as tourism, one might think science and technology have finally advanced enough to take the fiction out of sci-fi for our extraterrestrial activities.
Humans still know little about space, however. Whether launching additional communication satellites or building a space station, it’s important to understand exactly what goes on in the cosmic environment. After all, space isn’t exactly a hospitable place. Radioactive particles constantly rain down on planets, and asteroids crash and burn.
As scientists strive to untangle space mysteries, some of them are paying particularly close attention to a familiar phenomenon: Aurora.
As graceful as they may seem, auroras are the product of violent chain reactions of energy that originates in the sun. Certain types of auroras can produce enough currents to potentially destroy electrical substations on Earth, triggering rolling blackouts around the globe.
Complex and elusive, auroras have been a difficult subject for scientists to study. That’s changing, however, thanks to researchers’ creative uses of big data and information technology.
In this series, “Lifting the Curtain on Auroras,” some of Japan’s experts on the forefront of aurora research will discuss their discoveries and explain where they are headed in their endeavors.
Ask the Experts: Ryuho Kataoka (National Institute of Polar Research)
Ryuho Kataoka, associate professor at the National Institute of Polar Research (NIPR), specializes in studies of space physics and is known for his research on auroras and space weather forecasting. He is a recipient of the Ministry of Education, Culture, Sports, Science and Technology’s Young Scientist Award 2015, and hosts “Solar Flare and Space Disaster” on NHK Culture Radio. He is the author of many books, including “Aurora!” (2015) and “Space Disaster” (2016).
Ryuho Kataoka, associate professor at the National Institute of Polar Research, calls green auroras a “symbol of life.” Red auroras, on the other hand, signal potential “troubles for modern society,” he said.
That’s because auroras’ colors are indicative of how the sun’s energy interacts with that around Earth. Red hues indicate the presence of strong radiation that could fry satellites and knock down vital infrastructures that support our lives, while green hues represent an abundance of oxygen that keeps us alive.
“Studying auroras means understanding how space, Earth and the lives on it are all connected to each other,” Prof. Kataoka said.
In pursuit of truths about auroras, Prof. Kataoka uses the latest model of high-sensitivity cameras to observe the Alaskan night skies. Lately, he has also turned to an unlikely source of information: historical documents.
In 2017, his discovery of a 1770 painting of a red aurora made headlines across Japan. He and his research team found additional records from written archives that substantiated the painter’s visual account. Also in 2017, Prof. Kataoka produced many pieces of evidence that red auroras frequently appeared in Japan’s skies in the late 18th Century. His research demonstrated how the country was experiencing the effects of a giant magnetic storm at that time.
But, before going into the details of his findings, it may be helpful to review some basics.
What is an aurora? And, how do those magical light displays happen? And why do they come in different colors?
In space, various entities, including the sun, are emitting electromagnetic waves and cosmic rays, which consist of high-energy particles. When ionized particles released from the sun during an eruption known as a solar flare smash into Earth’s protective electromagnetic barrier, it sparks a massive amount of electricity -- so much so that it can light up the skies, creating beautiful displays that we all call auroras.
“Auroras require three ingredients: Super-hot plasma blown toward Earth, the electromagnetic shield surrounding Earth, and Earth’s atmosphere. Auroras are the result of high-speed collisions among these elements,” Prof. Kataoka said.
The produced electric current travels toward Earth’s North and South poles along the lines of magnetic force, forming a ring-shaped display, or an “aurora oval,” in the Arctic and Antarctic skies.
Aurora’s colors vary, depending on how far into the atmosphere auroral electrons travel. When they reach the oxygen-rich zone approximately 100 kilometers above Earth’s surface, the chemical reactions produce lights in green hues. Auroras take on reddish hues at 200 kilometers above the ground and purple hues at 90 kilometers.
Auroras can be seen above other planets, as well. Both Jupiter and Saturn have auroras in pink tones.
But, the curtain of green lights that many people equate with the word, “auroras,” can happen only above Earth, because it requires a lot of oxygen to generate the color, Prof. Kataoka said.
Use of cutting-edge technology to tackle challenges
While Auroras stand out in the night sky, humans cannot see them three-dimensionally with the naked eye as they are too far away for parallax to work. In 2010, Prof. Kataoka became the first person to successfully take three-dimensional photographs of auroras and to develop methods for calculating the distance between auroras and observation points.
“I am always interested in technologies that are advanced but easy to use and can help me get a more accurate picture of what aurora looks like,” Prof. Kataoka said. In recent years, he’s added a high-sensitive, fast-speed camera to his toolbox. “There’s only so much you can see with the naked eye. The combination of high-sensitivity and high-speed can be very helpful in understanding how auroras change and why,” Prof. Kataoka said.
Aurora is a highly complex phenomenon that can be examined from many different angles, according Prof. Kataoka.
“We could focus on plasma’s fluid dynamics, electromagnetism, or quantum aspect. Throughout the aurora-making process from the point where electrically charged particles spew from the sun to their collision with Earth’s atmosphere, the energy that connects space with Earth continuously changes in its form and level. The voltage can spike 1,000 times or plummet to a millionth of what it was between stages,” Prof. Kataoka said.
Aurora, radiation, cosmic rays and some other study areas share the same principles of physics. “Aurora crosses over all the areas in the most complex way,” he said. For example, he said, plasma’s fluid dynamics and electromagnetism are both well-studied areas with definable phenomena, Prof. Kataoka said. “But, we don’t necessarily know what exactly is happening in the area where the two cross over. We can apply our knowledge of fluid dynamics to understand the changes that happen slowly. As for changes that we cannot see, electromagnetism helps explain them. The problem is what’s in between,” he said.
“The solution may be a super-burst camera mode. By taking photos in an incredibly fast successions, we may be able to visually grasp where the two areas merge, and that, in turn, may provide a clue for understanding plasma physics and aurora phenomena more deeply,” Prof. Kataoka said. The cutting-edge camera that Prof. Kataoka uses for the observation of the Alaskan skies offers a burst-mode and high-sensitivity that enables him to capture changes more efficiently than the human eye could.
“I gather about 500 terabytes of data per year. I am anxious to find out what emerges out of this data and how that may change the way we look at auroras,” he said.
Historical documents: An unlikely ally of scientists
Innovative technologies aren’t researchers’ only ally.
From 2015 through 2017, Prof. Kataoka served as the director of “Aurora 4D Project,” a collaborative academic research by the National Institute of Polar Research, the National Institute of Japanese Literature and The Graduate University for Advanced Studies (SOKENDAI) to study historical materials and extract records of auroras and related incidents in Japan’s past to help advance aurora research and prevent the negative consequences of the phenomena in the future. The initiative emerged out of the cross-disciplinary working relationships fostered among these institutions, thanks to them being all located on the same research campus in the western Tokyo city of Tachikawa.
Among the materials the team studied was Meigetsuki, the diary of Fujiwara no Teika (1162–1241), one of Japan’s most legendary poets. In 2017, Prof. Kataoka released several research results concerning the records in Meigetsuki about people in Kyoto witnessing red auroras continuously over several days in February 1204. He and his team found in China’s History of Song, the official records of the Song dynasty (960–1279) that a big sunspot was observed on the same days as the aurora displays in Kyoto.
“Through some calculations, I figured out that the geomagnetic poles were tilted toward Japan at that time, and the chance of an aurora appearing in the Japanese skies was greater than at any time in the previous 3,000 years,” Prof. Kataoka said. “Through the Aurora 4D project, we determined Teika’s writing as the evidence of the oldest, continuous giant magnetic storm that impacted Japan.” (Click here for the press release.)
Literature from the Edo period (1603-1868) also indicated auroras appeared over Japan’s skies during this era, as well.
The red aurora in the colorful drawing that Prof. Kataoka discovered is believed to have appeared in September 1770. With bold brushstrokes, the artist depicted the rays of burning red light fanning out over the horizon. Prof. Kataoka said he first thought the dramatic expressions were just an art technique.
“I then realized a simulated image of the aurora, which was based on my calculations, looked exactly like the drawing I found in the archives. I was stunned by it,” Prof. Kataoka said. “Based on the latitude of the artist’s location, I was also able to calculate how much energy had built up in the magnetosphere and how strong the magnetic storm was. Once I had the scientific data to back up the drawing, I developed different perspectives for it. I know the aurora covered the entire sky, and that’s probably why the artist decided to draw it across two pages,” he said.
Aurora can appear anywhere in the world. When a giant magnetic storm blows, it can send electric currents down through Earth’s weakened magnetic shield to low-latitude areas where auroras wouldn’t appear otherwise. These auroras are in reddish hues.
“Where red auroras are, there’s extraordinarily strong radiation. It has the potential to cause artificial satellites to malfunction or destroy electrical substations, sending a wave of blackout globally,” Prof. Kataoka said. “Earth’s magnetic poles continuously move. For example, they are tilted toward the U.S. as of 2018, meaning if a magnetic storm happens, red auroras would more likely appear over the North American continent than anywhere else.”
Once a coronal mass ejection, or a solar eruption, occurs, the blast continues for about a week. That sends dangerous solar winds Earth’s way, creating “the worst space environment” for modern society, Prof. Kataoka said.
Forecasting Space Weather to Prevent Global Blackout
To prepare for such disasters, experts keep an eye on “space weather.” According to the forecasts available as of 2018, things are calming down compared to the past 50 years during which space experienced some turbulent weather with aurora ovals often exploding.
“That change is interesting in itself, too,” Prof. Kataoka said. “There may be new activities on the sun that we haven’t seen before. If cosmic rays strengthen while the sun quiets down, we’ll be able to see how that affects Earth and the overall space and terrestrial environment. In other words, we could observe changes unique to deep solar minimum.” he said.
Just because the sun is expected to become less active, that doesn’t mean we can forget about preventing global blackout, Prof. Kataoka warned. When solar winds aren’t strong, the lack of pressure can cause an explosion to grow larger, making it easier for radioactive particles to reach Earth, he said.
“Giant magnetic storms have historically occurred pretty randomly. We cannot let our guard down,” Prof. Kataoka said.
Did you know?
There’s nothing minimum about “solar minimum” when it comes to your radiation exposure, according to Shoko Miyake, associate professor at the National Institute of Technology, Ibaraki College.
“During a solar maximum -- which is marked by the sun’s increased activity and frequent appearances of sunspots -- cosmic rays tend to lose the energy and get pushed out of the heliosphere. During a solar minimum, on the other hand, the heliospheric magnetic field is well-conditioned for cosmic rays to travel through and reach down toward Earth more easily,” Prof. Miyake said.
The polarity of the sun’s magnetic field inverts every 11 years. As the sun grows more active, it causes confusions to the structure of current sheets, which makes swirls as it spreads out, Prof. Miyake said.
Prof. Miyake worked with Prof. Kataoka to develop a cosmic ray propagation model that takes this cycle of polar inversion into consideration, so she can forecast the year-by-year changes in the level of radiation exposure that one would have while aboard an airplane at high altitudes. She has forecasted through 2024 so far. The average exposure level over the 5-year period during which the next inversion occurs is expected to be 19 percent higher than the average exposure during the five-year period during which the previous inversion happened, according to Prof. Miyake. (Click here for the press release.)
By finding out what kind of cosmic rays are out there and how much of those are being received by Earth, researchers can begin to figure out how the vast universe surrounding the solar system works, Prof. Miyake said.
“Cosmic rays show us the part of the universe we humans cannot reach,” she said.
Interviewer: Rue Ikeya
Photographs: Yuji Iijima unless noted otherwise
Released on: Aug. 9, 2019 (The Japanese version released on Aug. 10, 2018)