A University of Southampton study has revealed an intriguing new clue to the mystery of what triggers periods of very intense, brightly colored activity during displays of the Northern and Southern Lights.
Auroral pearls seen from the International Space Station. Credit: NASA
Known as a “magnetospheric substorm,” this impressive phenomenon, which blankets the night sky in green and purple, is almost always preceded by what space scientists call “auroral beads” – a necklace-shaped wave of multiple bright points of light that eventually evolve into a storm.
Southampton scientists have now shown that there is a link between these auroral beads and the intensity of low-frequency radio waves above auroras in Earth’s magnetosphere – a large area around our planet dominated by its magnetic field.
Their findings are published in the journal Natural Communications.
“The Northern Lights and Southern Lights are caused by charged particles from space colliding with atoms and molecules in our atmosphere,” explains the physicist. Dr Daniel Whiter from the University of Southampton. “Particles ejected from the Sun pass through the solar system, carrying with them the Sun’s magnetic field, and this “solar wind” is the source of energy for auroras.
“Auroral substorms are caused by the accumulation and then release of magnetic energy stored in Earth’s magnetosphere as it interacts with the solar wind flow. However, what exactly triggers the sudden and dramatic discharge of this energy is not fully understood.”
An international team of researchers, led by physicists from Southampton, examined data collected from ground-based observatories, imaging satellites and radio antennas aboard spacecraft, including NASA’s “Polar” spacecraft, Japan’s “Arase” spacecraft and cameras stationed in Lapland operated by the Finnish Meteorological Institute.
In particular, the team focused on examining auroral kilometer radiation (AKR) – natural radio emissions produced in near-Earth space, directly above auroras.
The scientists found that before a substorm appeared, there was a distinct signal in the AKR activity almost exactly when the auroral beads became visible. This burst of radio wave emissions suddenly increases in intensity at the start of the substorm.
Studied for the first time, this distinct radio signal provides important clues about the physical processes operating before and during the onset of substorms, producing signatures in both visible aurora and invisible radio emissions.
Lead author of the study, postdoctoral researcher Dr Siyuan Wu from the University of Southampton comments: “The fine frequency-drift structures observed in the AKR provide direct evidence for the formation of small-scale electric potential structures along magnetic field lines connected to the auroral beads. Their periodicity and propagation speed show remarkable consistency across multiple data sets.”
“Together, these results provide new evidence on the generation of auroral beads and the substorm triggering process.”
Scientists believe it could be a universal mechanism manifesting itself not only in Earth’s northern and southern lights, but also in the magnetosphere of some other planets in our solar system, such as Saturn and Jupiter. They hope their research can now be deepened to fully understand what triggers auroral substorms.
Source: University of Southampton
Originally published in The European Times.
source link eu news
