The Van Allen radiation belts in in the Earth's upper atmosphere, two doughnut-shaped rings of highly charged particles, were discovered in 1958. The Van Allen radiation belts consist of an inner ring of high-energy electrons and energetic positive ions, and an outer ring of high-energy electrons.  

But then in February of this year, a team of scientists writing in Science reported a previously unknown third radiation ring, which circled the Earth between the inner and outer rings in September 2012 and then almost completely disappeared.  

How did this temporary radiation belt appear and dissipate?

Writing in
Geophysical Research Letters, the radiation belt group in the UCLA Department of Atmospheric and Oceanic Sciences explains the development of this third belt and its decay over a period of slightly more than four weeks. By performing a "quantitative treatment of the scattering of relativistic electrons by electromagnetic whistler-mode waves inside the dense plasmasphere," the investigators were able to account for the "distinctively slow decay of the injected relativistic electron flux" and demonstrate why this unusual third radiation belt is observed only at energies above 2 mega-electron-volts.  

Understanding the processes that control the formation and ultimate loss of such relativistic electrons is a primary science objective of the NASA Van Allen Probe Mission and has important practical applications, because the enormous amounts of radiation the Van Allen belts generate can pose a significant hazard to satellites and spacecraft, as well to astronauts performing activities outside a spacecraft.

The current research was funded by the NASA, which launched the twin Van Allen probes in the summer of 2012.