Abstract

Large explosions on the Sun can expel billions of tons of charged particles and magnetic field out into space in what is known as a coronal mass ejection. When this plasma encounter’s the Earth’s magnetic field it can tear open the outer layers of the field and cause a geomagnetic storm which can last for days. Magnetic storms can cause disruption to power supplies, satellites, positioning and timing signals, aviation and a host of other businesses. Here we describe what happens to the Earth’s radiation belts and how they present an enhanced risk of radiation damage to satellites. The radiation belts consist of high energy (relativistic) electrons and ions trapped inside the Earth’s external magnetic field and which circulate round the Earth on a period of tens of minutes. The science problem is to understand how the particles are accelerated, and what causes the variability. We show how the original ideas on how the radiation belts are formed have been changed by new research and discuss the two leading acceleration processes, acceleration by very low frequency radio waves, and acceleration by radial transport. We describe a new system that has been developed in the EU SPACECAST and the SPACESTORM projects to forecast radiation levels throughout the radiation belts and assess the risk to satellites on orbit. Finally, we show how electron acceleration by very low frequency radio waves could be a major process for forming the radiation belts at Jupiter and Saturn.