Scientists once thought that there were only two Van Allen belts, regions within the Earth's magnetosphere where high-energy protons and electrons are trapped by the magnetic field of the planet.
Since 1958, the regions were classified into the inner and outer belts but in 2013, NASA's twin Van Allen Probes, which were sent to map out the region, observed the presence of a third belt. Scientists were able to observe the third Van Allen belt for four weeks before it was destroyed by powerful interplanetary shock wave from the sun.
Scientists have been baffled by the temporary appearance of the third radiation belt but researchers from the University of Alberta appear to have found what was behind its formation.
In a new study published in the journal Nature Physics on Monday, University of Alberta physics professor Ian Mann and colleagues wanted to model the process by which plasma waves in the Earth's magnetosphere influence the dynamics of particles in the Van Allen belts that move in relativistic speed.
The study has led the researchers to conclude that the third radiation belt was created by intense ultra-low frequency (ULF) plasma waves that wash over the magnetosphere. The waves' movement caused the outer belt to break off and resulted in the temporary formation of a third outermost layer of charged particles.
The researchers said that they have observed the plasma waves move in a space-tsunami like fashion.
"Remarkably, we observed huge plasma waves," Mann said. "Rather like a space tsunami, they slosh the radiation belts around and very rapidly wash away the outer part of the belt, explaining the structure of the enigmatic third radiation belt."
Solar wind from the sun is an important energy source for ULF waves. The researchers noted of the importance of studying these plasma waves to reduce threats of space radiation that may potentially destroy the Earth's satellites. The GPS and satellite-based telecommunications that modern society relies on today are affected by the radiation within the Van Allen belts.
"Using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we show for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport," the researchers wrote in their study.
"When rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained."