Earth: Ring Current
Earth: Ring Current
Radiation BeltsIntroduction
The ring current extends from 8,000 kilometers to nearly 30,000 kilometers from the surface and occupies nearly the same zone as the much more energetic Van Allen Belts. Ring current particles carry energies of thousands of volts. It is not a complete equatorial ring, like the planet Saturn’s rings, but is only at its strongest on the night-side of the Earth. Its strength increases and decreases with the activity in the magnetotail region.
River of Charged Particles
During times of severe storminess, when the solar wind magnetic polarity is south-type, the ring current becomes a powerful river of charged particles that create their own intense magnetic field. This field modifies the Earth's own field and actually decreases its intensity in the equatorial regions of the Earth. The origin of these 100,000-volt particles is something of a scientific mystery. We don't fully understand how they are energized to such high voltages within the magnetosphere.
Most of the time, the ring current 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?
The ring current images by the NASA IMAGE satellite. Looped lines show representative magnetic field lines. The circle represents Earth. Sunlight is from the lower-left corner.
The ring current images by the NASA IMAGE satellite. Looped lines show representative magnetic field lines. The circle represents Earth. Sunlight is from the lower-left corner. (Source: IMAGE-NASA)
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.
Images of Ring Currents
Spectacular images obtained by the IMAGE satellite show both partial and complete ring currents. For the first time, scientists can now see ring current particles flow from the night side to the day side of Earth and disappear into the magnetopause. The satellite observations also show that this is the most important way that these particles are lost from the current during a magnetic storm.
View Quicktime ring-current movie
Click on this image to view the Ring Current Quicktime movie.
External Links
- IMAGE Science Center - Imager for Magnetopause-to-Aurora Global Exploration, Goddard Space Flight Center, NASA. (Curator: Dr. S. Odenwald.)
- IMAGE Discoveries - IMAGE Education Center - Imager for Magnetopause-to-Aurora Global Exploration, Goddard Space Flight Center, NASA. (Curator: Dr. S. Odenwald.)
- Scientists Startled to Observe an Incomplete Ring Current (IMAGE Discoveries - NASA)
Preview Image
- Radiation Belts by David P. Stern.
Citation
Odenwald, Sten, Ph.D. (Contributing Author); Bernard Haisch (Topic Editor). 2008. "Earth: Ring Current." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published November 25, 2007].
<http://www.cosmosportal.org/articles/view/135527/>
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