Rights: © Copyright 2014. University of Waikato. All Rights Reserved. Published 29 April 2014 Download

Associate Professor Craig Rodger, Space Physics group leader at the University of Otago, explains what the Van Allen belts are. He then describes the effect a coronal mass ejection (CME) can have on them as a result of the Earth’s magnetic field being squeezed. Craig’s research interest lies in the changing chemical balance of the upper atmosphere induced by such changes.


Around the Earth – normally embedded in the plasma that surrounds the Earth – there are the Van Allen radiation belts, which are essentially a sea of trapped electrons and protons, bouncing in the magnetic field of the Earth [makes sound effect] on both sides of the Earth – like a doughnut around the Earth. Now, they’re trapped in the magnetic field, and when a CME comes along, the magnetic field gets distorted [makes sound effect], squeezing it, and that’s going to directly impact what happens inside the Van Allen belts. Because those particles, they’re trapped in the magnetic field, and I’ve just gone away and squeezed the field. You end up destabilising the belts.

A bunch of things happen inside the radiation belts that frankly we’re still trying to understand, but one of the things that happens is that some of the high-energy particles that previously were trapped in the magnetic field of the Earth end up falling out the ends. And the ends of the magnetic field connect up to the high latitude regions – the Arctic in the northern hemisphere and the Antarctic in the southern hemisphere – so those particles squirt into the atmosphere in the Poles. And that’s one of the things that I’m really interested in. I’m interested in how those losses occur in the radiation belts – how the particles come out of space – but also, when they splat into the atmosphere, what does that do?

We know for sure that, at high altitudes when those particles come out of space and zap the atmosphere, it’s like a [makes sound effect] – the energy comes down and zaps the atmosphere. It changes the chemical balance at high altitude, it produces chemicals that are present but in small concentrations. The ones that we tend to focus on are called odd nitrogen and odd hydrogen. Those chemicals are ozone destroyers. And so during a big storm at high altitudes, at 70 kilometres or so, you end up with less ozone being present than you would expect.

Associate Professor Craig Rodger, University of Otago, Department of Physics

NASA/Van Allen Probes/Goddard Space Flight Center