Scientists make first direct observation of electrons creating Northern Lights

I found this very interesting, so I’m passing it along to WUWT readers.

The shower of electrons bouncing across Earth’s magnetosphere – commonly known as the Northern Lights – has been directly observed for the first time by an international team of scientists. While the cause of these colorful auroras has long been hypothesized, researchers had never directly observed the underlying mechanism until now.

The scientists published their results today in Nature.

The spectacle of these subatomic showers is legendary. Green, red, and purple waltz across the night sky, blending into one another for a fantastic show widely considered one of the great wonders of the world. Among a variety of auroras, pulsating auroral patches appearing at dawn are common but the physical mechanisms driving this auroral pulsation had so far not been verified through observation.

With the advent of a new satellite with advanced measuring tools, researchers have now identified that this wonder is caused by the hard-to-detect interaction between electrons and plasma waves. This interaction takes place in the Earth’s magnetosphere, the region surrounding the Earth in which the behavior of the electric particles is usually governed by the planet’s magnetic field.

“Auroral substorms … are caused by global reconfiguration in the magnetosphere, which releases stored solar wind energy,” writes Satoshi Kasahara, an associate professor in the Department of Earth and Planetary Science at the Graduate School of Science of the University of Tokyo in Japan, the lead author of the paper. “They are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that eventually break up, and emerge as diffuse, pulsating auroral patches at dawn.”

The global reconfiguration often drives a specific type of plasma waves called chorus waves, to rain electrons into the upper atmosphere. This stabilizes the system, and gives off a colorful light as the electrons fall. However, scientists have questioned if the chorus waves were powerful enough to excite electrons to the extent of creating auroras.

Video: Pulsating aurora, the origin of the blinking patches of light, is now directly observed by the ERG spacecraft. Electrons in the magnetosphere, which usually bounce along the geomagnetic field, are thought to be scattered by chorus waves, resulting in precipitation into the atmosphere. The intermittent bursts of chorus waves cause the pulsations of precipitation and associated auroral illumination. The ERG spacecraft showed that this electron scattering by chorus waves indeed takes place in the magnetosphere. CREDIT 2018 ERG science team.

“We, for the first time, directly observed scattering of electrons by chorus waves generating particle precipitation into the Earth’s atmosphere,” Kasahara says. “The precipitating electron flux was sufficiently intense to generate pulsating aurora.”

Scientists couldn’t see this direct evidence of electron scattering before because typical electron sensors cannot distinguish the precipitating electrons from others. Kasahara and his team designed a specialized electron sensor that observed the precise interactions of auroral electrons driven by chorus waves. The sensor was aboard the Exploration of energization and Radiation in Geospace (ERG) satellite, also known as the Arase spacecraft, launched by the Japan Aerospace Exploration Agency.

The scientists plan to pursue this line of research further. The collaborative team includes not only researchers from the University of Tokyo, but also Nagoya University, Osaka University, the Institute of Space and Astronautical Science, Kanazawa University, and Tohoku University in Japan; the Academic Sinica Institute of Astronomy and Astrophysics in Taiwan; and the University of California, Berkeley and the University of California, Los Angeles in the U.S.

“By analyzing data collected by the ERG spacecraft more comprehensively, we will reveal the variability and further details of plasma physics and resulting atmospheric phenomena, such as auroras,” Kasahara says.



Journal article:

S. Kasahara, Y. Miyoshi, S. Yokota, T. Mitani, Y. Kasahara, S. Matsuda, A. Kumamoto, A. Matsuoka, Y. Kazama, H. U. Frey, V. Angelopoulos, S. Kurita, K. Keika, K. Seki, and I. Shinohara, Pulsating aurora from electron scattering by chorus waves, Nature

URL (abstract):

42 thoughts on “Scientists make first direct observation of electrons creating Northern Lights

  1. However, scientists have questioned if the chorus waves were powerful enough to excite electrons to the extent of creating auroras.
    So, all that happened was to put down the [few] scientists who questioned the mechanism.

  2. Real science. We had inferred what caused auroras, but now have direct observatiins proving the theory correct. Have seen spectacular auroras twice. Once before midnight west of Madison driving to the farm in dead of winter. We pulled over and got out so the kids could appreciate the whole sky view. Once at the cabin in Ontario over Christmas holidays. Both nights very cold and crystal clear.

  3. This story is yet another typical overhyped misrepresentation of the facts. It is about the diffuse aurorae that are at the limit of visibility [and sometimes pulsates in patches], not about the brilliant displays that are so impressive.

      • They are totally unrelated, as the bright aurorae are caused by electrons accelerated on field lines reaching out in the outer magnetosphere.
        “The immediate cause of the ionization and excitation of atmospheric constituents leading to auroral emissions was discovered in 1960, when a pioneering rocket flight from Fort Churchill in Canada revealed a flux of electrons entering the atmosphere from above. Since then an extensive collection of measurements has been acquired painstakingly and with steadily improving resolution since the 1960s by many research teams using rockets and satellites to traverse the auroral zone. The main findings have been that auroral arcs and other bright forms are due to electrons that have been accelerated during the final few 10,000 km or so of their plunge into the atmosphere. These electrons often, but not always, exhibit a peak in their energy distribution, and are preferentially aligned along the local direction of the magnetic field. Electrons mainly responsible for diffuse and pulsating auroras have, in contrast, a smoothly falling energy distribution, and an angular (pitch-angle) distribution favouring directions perpendicular to the local magnetic field. Pulsations were discovered to originate at or close to the equatorial crossing point of auroral zone magnetic field lines”
        Wikipedia [but good enough].

  4. So they have now explained the Aurora Borealis but there are also the A. Australis to explain. Because the Australis occur in the southern hemisphere there must be a shortage of electrons to produce them i.e. a different mechanism. Could this presumably positively charged mechanism also be part of the reason for the difference in ozone depletion between the north and south polar regions?

    • No, they had it over the barely visible diffuse aurorae and there is no difference between then northern and southern hemispheres. In fact, the particles bounce back and forth between the hemispheres several times a second.

        • No, not at all. Aurorae are created by charged particles moving along magnetic field lines and are seen at high latitudes. Airglow is due to recombination of ions and electrons generated by ultraviolet radiation from the sun and are therefore best seen at low latitudes.

  5. Leif, have you seen Don Scott’s bessel function solutions of the equations for force-free field aligned currents?
    Birkeland Currents: A Force-Free Field-Aligned Model
    I know (or at least I think I know) that you do not think much of the EU crowd and their ideas, but putting that aside, and in the interest of always keeping an open mind, have you seen that his solutions yield multiple concentric counter-rotating currents that look very similar to the multiple concentric counter-rotating atmospheric currents Saturn and Jupiter, and to the motion of Earth’s aurorae, when looking down the axes of rotation?
    He has a two hour presentation on this, but here is a very short, and necessarily far more incomplete description of his findings, and a visual correlation with observations from Saturn and Jupiter. (Jump to 1:20 … then it’s about 5 minutes.)

  6. Leif, if the Earth’s magnetic field is weakening (prior to reversing the magnetic poles), how will this affect auroral displays? And will they move further south (or north) over time?
    I didn’t get to see any of this, thanks to overcast weather, so thanks in advance for responding.

  7. Came across this while looking for something else and was astonished that
    “new” science was something I knew when I wrote my thesis on pulsating
    aurora in the early 70s. But can anybody explain that “black” aurora shows
    both pulsations and curls. I can’t remember what way the curls rotate. Have
    not worked on this in 40 years.

  8. Fake news. Everyone knows–as Robert Service told us–that the Northern Lights are caused by a “a mine of the precious stuff that men call radium.” In the Yukon Territory. “It’s a million dollars a pound, they say, and there’s tons and tons in sight. You can see it gleam in a golden stream in the solitudes of the night.”

  9. I think the problem is in the linguistics. Using words used to describe the behavior of gases and liquids to describe the actions of plasma. Rain, wind, precipitate (implying from a cloud like in the atmosphere) – currents implying circuits is ok there is an electrical current between the Earth and the Sun (one manifestaton being the aurora). then there is the use of field lines – magnetic fields don’t have lines except in wrong physics (belief in monopoles or magnetic reconnection) or a useful simplification for mathematical calculations – similar to the belief that fluid dynamics (used for liquids and gases) can describe the phenomena of plasma .

    • “Except that the auroral Birkeland currents don’t look like that”
      Agree, it is not a typical aurora, if the date is available, solar end geomagnetic conditions research, as in the high frequency active auroral research program, may give more insight/sarc.

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