The Ring Current.

Most of the time, it is not there at all. In a special slot between 2Re and 6Re, conditions seem to be just right that whenever a severe solar storm impacts the magnetosphere, particles appear 'out of nowhere' to fill this region with very energetic particles. One big clue about where they come from has to do with satellite measurements of the kinds of particles found there during a storm. They are mostly oxygen ions! The only nearby source of oxygen ions is Earth itself. How do they get there?

When we discussed the ionosphere and the plasmasphere, we noted that under certain stormy conditions a fountain of oxygen and nitrogen ions can be launched from the polar regions into space. Scientists think that this is where the Ring Current particles come from, but we still are not sure how it is that low-energy ions from the atmosphere can get boosted by over 1000 times in energy to become part of the ring current. There is some evidence that the origin of this energy comes from processes that are going on even farther from the Earth that heat the Ring Current plasma to high energies.

The ring current is seldom seen unless a major solar storm has just impacted the magnetosphere. Immediately after the storm begins, the ring current brightens and begins to flow around the Earth from the nighttime side to the daytime side. Along the way, its inner edge invisibly rubs against the outer regions of the plasmasphere. Plasmasphere ions pick up energy and are convected with the ring current flow to mingle their matter with this current. The ring current produces its own magnetic field, which interacts with Earths field over the equatorial regions. A significant reduction in the magnetic field at the surface of Earth often goes along with the formation of the ring current. As the storm slackens, the ring current ions rapidly diminish in numbers, perhaps because of collisions with the slower moving plasmasphere particles, and as mysteriously as it appeared, it vanishes. IMAGE satellite observations can watch the entire evolution of this system of plasma, and this has revealed many exciting new clues about how the Ring Current is produced, but there is still much more to learn!