How do you study something like this? Well, first, a little more about the Van Allen radiation belts: There are two of them, one orbiting at a distance of some 8,000 to 40,000 miles above the Earth, and another inner band at about 600 to 3,700 miles. NASA has a pair of satellites called the Van Allen Probe satellites which were launched in 2012. Circling the Earth in eccentric orbits around the equator at altitudes of up to 20,000 miles, about once every nine hours, they cover the entire radiation belt region. That gave Milan and her team data about the particles trapped in the Van Allen belts. To gather information about the particles that manage to migrate from the Van Allen belts into the Earth's atmosphere, they've been using a fleet of helium balloons launched from Antarctica, some rising as high as 125,000 feet into the atmosphere. Each balloon carried a sensor array that recorded the X-rays produced as the falling electrons collided with the atmosphere.
"Our paper looked at plasma waves," explains Millan. "These are like sound waves in air except that now you are in an ionized gas so the electric and magnetic fields are affected. ... What the paper shows is that we observed these waves at the location of the Van Allen probes. We saw electric and magnetic field variations that displayed a pattern, matching the variations in the X-rays we were recording in Antarctica. ... We concluded that those waves were causing the electrons to be scattered, yielding a new understanding of how the particles are getting kicked into the atmosphere. We are learning about processes that can affect our lives directly, when active in our planetary environment. These same processes are probably happening throughout the universe and, with the tools at our disposal, we can study them in detail right here."
(Sources: phys.org, NASA, Wikipedia)