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Pieces of the Sun: Earth’s Aurorae Phenomena

Yohsuke Kamide Director, Rikubetsu Space and Earth Science Museum

The aurora, an enchanting dance in the starry sky, is a magical sight that many of us dream of seeing at least once in our lives. Aurorae occur in the near-Earth space environment, which is called geospace. Geospace is filled with solar wind blown from the Sun; the energy generated there creates aurorae. But how does this process work? And how is it related to what happens on the aurora’s home, the Sun? We asked a leading expert in aurora research, Professor Yohsuke Kamide.

Yosuke Kamide, Ph.D.
Director of the Rikubetsu Space and Earth Science Museum, Professor Emeritus at Nagoya University.
After graduating from the School of Science at Hokkaido University and from Graduate School at the University of Tokyo, Prof. Kamide moved to the United States. There, he worked at the Geophysical Institute of the University of Alaska Fairbanks, the Institute of Research in Environmental Science of the University of Colorado Boulder, the National Geophysical Data Center, the National Space Environment Laboratory, and the National Center for Atmospheric Research. In 1992, he became a professor at the Solar-Terrestrial Environment Laboratory of Nagoya University in Japan. After serving as director of the laboratory from 1999 to 2005, he was appointed professor at the Research Institute for Sustainable Humanosphere at Kyoto University. In 2010, he became the director of the Rikubetsu Space and Earth Science Museum. In recognition of his comprehensive research on the generation of aurora borealis and his foundational work on space weather forecasting, Prof. Kamide has received many awards, including the 2003 Price Medal of Britain’s Royal Astronomical Society, and the 2012 Axford Medal of the Asia Oceania Geoscience Society. He is the author of numerous books on the Sun, aurorae, and geomagnetic storms.

  • From the Sun to the Earth
  • The hunt for aurorae
  • A lucky miss
  • Solar aurorae create the Earth’s aurorae
  • Something unexpected is happening to the Sun!?
  • There will be aurorae as long as the Sun exists
  • I like studying the unknown
  • An aurora is a message from the Sun
  • Japan to lead the world with its own satellite
  • Break the culture of silence and challenge the world!

From the Sun to the Earth

--- Could you tell us about your research to date?

The focus of my research is, in short, to explain the unique relationship between the Sun and the Earth. For instance, let’s say the Sun is the size of your head. How many meters away do you think the Earth would be, and how big would it be in comparison? The answer is that our globe would be 30 meters away and its diameter would be 2 millimeters. Paying no attention to our tiny planet, the Sun keeps emitting solar wind, X-rays and ultraviolet rays. And among these emissions, I have been studying the electromagnetic phenomena caused by the interaction between solar wind, which is in effect a plasma stream, and the Earth’s magnetic field. One of the phenomena is aurorae, about which we still know very little.

--- Are there still unknowns about aurorae?

Solar wind and the Earth’s magnetosphere (courtesy: Prof. Kamide)
Solar wind and the Earth’s magnetosphere (courtesy: Prof. Kamide)

Let me give you a brief description of how they are generated. An aurora is created by solar wind emanating from the Sun. Solar wind consists of plasma particles. These particles are emitted from the Sun, and become luminous when they collide with the upper atmosphere near the Earth’s poles. That’s what an aurora is – it’s a kind of electrical-discharge phenomenon, which takes place between 100 and 500 kilometers above the ground, caused by plasma particles that glow as they collide with atoms and molecules in the atmosphere. The colors vary depending on the atoms and molecules the plasma particles interact with: whitish green or red when they collide with oxygen atoms, and purple or blue when they collide with molecular nitrogen.

The Earth’s magnetosphere stretches like a long tail on the night side of the planet, and plasma particles gather in the vicinity of the center of the night side of the magnetosphere. Then something directs them to stream towards the Earth’s polar regions all at once. We still don’t have a good understanding of how this occurs. There are also aurorae that suddenly brighten the sky, as a burst of light, around midnight, and then spread out dynamically all at once. This phenomenon is called an aurora breakup or explosion, and this process has not been explained either.

The hunt for aurorae

--- Among all the research results you have achieved in your career, which one stands out the most?

Aurora photographed in Norway (courtesy: Ole C. Salomonsen)
Aurora photographed in Norway (courtesy: Ole C. Salomonsen)

Every aurora has a powerful electric current running through it. In the case of a powerful aurora, the total current reaches millions, or tens of millions, of amperes, with voltages of hundreds of kilovolts. Based on data about the Earth’s magnetic field, I have come up with a method for calculating the electric field and current that create aurorae. This method allows us to determine the location and scale of any aurora that is occurring at a given moment, as long as we have ground magnetic variation data.

To be more precise, there are more than 100 stations on Earth to observe the planet’s magnetic field, including three stations in Japan: Memanbetsu, Hokkaido prefecture; Kakioka, Ibaraki prefecture; and Kanoya, Kagoshima prefecture. Using observation data collected at these points, I developed a method to determine the location of the electric current causing the Earth’s magnetic field, and where the electric field, which conveys the electric charge, comes from. This is like making a world map of the electric potential relating to aurorae based on the distribution of ground magnetic variations. After more than 10 years of thinking, I was finally able to publish a paper in 1981, and instantly received good responses and positive evaluations from around the world.

--- It was good that you didn’t give up.

This is a little technical, but I attempted to detect electric fields that create aurorae based on Ohm’s law, which states “electric current = electrical conductance x electric field.” Ohm’s law can be put in a differential equation when it is written with electric potential, so I knew that I needed to solve it mathematically. However, the differential equation was so difficult nobody had been able to solve it for a hundred years.

For about 10 years, whenever I had time, I opened a notebook and tried to solve the equation, but I couldn’t. And then one day, when I was almost tempted to give up, the solution came to me. With this idea, I visited an American friend of mine, Dr. A.D. Richmond, and became sure that I would be able to solve the equation with the help of his mathematical genius. And the following year I finally succeeded, using the large computer at the U.S. National Center for Atmospheric Research.

A lucky miss

--- Powerful aurorae originate in masses of plasma released by a solar flare. In May 2013, four solar flares were observed consecutively, and the media were reporting that the Earth would be hit by the most intense solar wind in the current solar cycle.

Low-latitude aurora seen in Missouri, USA on October 24, 2011 (courtesy: Tobias Billings/NASA)
Low-latitude aurora seen in Missouri, USA on October 24, 2011 (courtesy: Tobias Billings/NASA)

Aurora seen in Rikubetsu, Hokkaido, Japan on October 30, 2003 (courtesy: Rikubetsu Space and Earth Science Museum)
Aurora seen in Rikubetsu, Hokkaido, Japan on October 30, 2003 (courtesy: Rikubetsu Space and Earth Science Museum)

Luckily, there was no serious damage this time because the solar wind did not hit the Earth directly. However, highly charged particles released from solar flares can cause severe damage to infrastructure on the Earth, such as communications and power grids, as well as instruments on satellites. Through auroral currents, solar flares can also cause blackouts and interfere with satellites’ orbits.

From May 13 to 15 this year, four of the most powerful “X-class” solar flares occurred in a row, and an alert was issued in anticipation of serious damage that would be caused if the Earth took a direct hit. It did not happen this time, but part of that powerful solar wind entered the Earth’s magnetosphere, and a red, low-altitude aurora occurred above Colorado, in the United States. If it had been night time with a clear sky in Japan, we would have seen an aurora in Hokkaido, too.

--- How far in advance is it possible to predict the influence of solar flares on aurorae?

I would say two to three hours in advance for accurate prediction. There are also explosions different from solar flares, called corona mass ejections (CMEs). Both solar flares and CMEs – which cause aurorae and geomagnetic storms – occur unexpectedly, so it’s impossible to predict aurorae and geomagnetic storms until just before their arrival at a satellite in the near-earth solar wind. However, to try to mitigate damage as much as possible, solar activity is monitored around the clock, both via satellites and from the ground, to track the probability of coming space storms. This is called space weather forecasting. JAXA’s solar physics satellite HINODE is one of the satellites that are contributing to this.

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