Ions rain down over earth's poles.

Ions rain down over Earth's poles

In the mid-1970s, scientists discovered that electrons flowing away from the sun can latch on to Earth's magnetic field lines and follow a path to the planet's poles, where they penetrate the extreme upper layer of the atmosphere--a phenomenon known as electron polar rain. Physicists have long suspected that solar protons similarly nose their way to Earth's poles, but studies of satellite measurements have only once detected a glimpse of what is called ion polar rain. Now researchers have caught a second, more definite view.

On Dec. 10, 1983, instruments aboard two polar-orbiting satellites measured a large swarm of positive ions, located about 800 kilometers over the poles, report Patrick T. Newell and Ching Meng of the Johns Hopkins Applied Physics Laboratory in Laurel, Md., in the September GEOPHYSICAL RESEARCH LETTERS. The ion flow on this day was about 10 times stronger than that during the first detection of ion polar rain.

In their continuing analysis of the satellite data Newell and Meng have found seveal more instances of the rare ion rain, which is probably mostly protons, Meng says. It is still unclear exactly how electrons and ions in the solar wind can pass through Earth's magnetic barrier, called the magnetopause. One theory suggests the particles flow around Earth and then come up from behind the planet. Since fleet electrons could follow this route better than slower ions, this may explain why ion rains is rarer than electron rain. Further studies will help resolve the path of the particles, Meng says.