Inner Radiation Belt Surrounding Earth Organized in Zebra Stripe Patterns

Posted on March 22, 2014

There are two giant belts of radiation surrounding Earth. The inner belt is dominated by electrons while the outer belt is dominated by protons. Both belts are trapped there by Earth's magnetic field. Astronomers using NASA's twin Van Allen Probes found that the inner radiation belt displays a persistent pattern resembling slanted zebra stripes. Astronomers have also determined that the reason this pattern exists is because of the slow rotation of the Earth. Previously, it was believed that any structures or patterns were caused by solar winds. Astronomers discovered the zebra stripe patterns were present even during low solar wind activity so they knew something else was causing the patterns.

Aleksandr Ukhorskiy, lead author of the paper at The Johns Hopkins Applied Physics Laboratory (APL), says in the announcement, "It is because of the unprecedented resolution of our energetic particle experiment, RBSPICE, that we now understand that the inner belt electrons are, in fact, always organized in zebra patterns. Furthermore, our modeling clearly identifies Earth's rotation as the mechanism creating these patterns. It is truly humbling, as a theoretician, to see how quickly new data can change our understanding of physical properties."

Earth's rotation generates an oscillating, weak electric field that permeates through the entire inner radiation belt. This is due to the tilt in Earth's magnetic field axis. Ukhorskiy suggests imaging electrons are like a viscous fluid so you can understand how the electric field generated by the Earth's rotation affects the electrons. He says the global oscillations slowly stretch and fold the fluid which results in the striped pattern observed in the inner belt. He compares this to taffy being stretched and folded by a candy store machine. Take a look:


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