Near-Earth space shows its stripes

Abstract

Electrons in Earth's magnetic field often exhibit a striped pattern of intensity as a function of electron energy and altitude. A model that factors in some unexpectedly important effects can now explain this feature. See Letter p.338 Earth's radiation belts are populated by electrons and ions that are held in place by a magnetic field. Structured features in these belts have previously been attributed to enhanced solar wind activity. Although planetary rotation is considered to have an important role in driving belt dynamics around Jupiter and Saturn, it has been thought inconsequential for Earth's radiation belts, where the forces involved are much smaller. A new analysis of data from the Van Allen Probes mission shows that the distributions of energetic electrons across the entire spatial extent of Earth's inner radiation belt are organized in regular, highly structured, and unexpected 'zebra stripes' even when the solar wind activity is low. Modelling reveals that the patterns are produced by planetary rotation, which induces global diurnal variations of magnetic and electric fields that resonantly interact with electrons whose drift period is close to 24 hours.