Solar Storms Could Bring Northern Lights South

Increased solar activity could give residents of the continental U.S., southern Europe and Japan the chance to see the northern lights for the first time in several years.

The National Weather Service's Space Weather Prediction Center says the sun is entering a period of high activity, marked by more sunspots and a greater chance of a coronal mass ejection, or CME, hitting the Earth. That would result in auroras being visible much further from the poles than they usually are.

A CME is essentially a blast of charged particles (mostly protons and electrons) that speeds outward. Most of them pass by and humans never notice, but occasionally the Earth is in the way. When that happens, the particles - enough to weigh as much as a small asteroid -- hit the Earth's magnetic field and get trapped.

They then are pushed at high speeds to the polar regions, where they hit the atoms of oxygen and nitrogen in the atmosphere and ionize them. The atoms release energy as light and form the aurora borealis, or northern lights. (The same thing happens in the southern hemisphere, where it is called the aurora australis). That is why the closer to the poles you are, the better chance you have of seeing the auroras.

Usually the number of charged particles is small and the lights aren't visible very far from the poles. But in periods of heavy solar activity, CMEs happen more often. That makes it more likely that the Earth will get hit with a large, intense blast of charged particles. When that happens, more of the atmosphere is ionized and the effect extends further from the poles, to the point that with luck, people as far south as Texas might see it.

The sun goes through regular, 11-year cycles of low and high turbulence. For the past several years it has been at a minimum. But over the next two years there will be more activity in the sun's magnetic field, which will create unstable regions in the corona, the outer part of the sun's atmosphere that is visible during total eclipses. That means more CMEs.

The CMEs have other effects as well. A particularly intense one can damage satellite electronics if they aren't shielded well. When CMEs hit the Earth's magnetic field, they compress it on one side. Many satellites use the magnetic field to orient themselves, so when the field disappears for a time their onboard navigation systems get confused.

In 1994, a CME caused a geomagnetic storm that knocked out a Canadian communications satellite, costing some $50 million. In April, Intelsat's Galaxy 15 satellite was knocked out by solar activity, though it was rebooted this week and appears to be responding to commands again.

Joe Kunches, space scientist at NOAA, said the biggest effects are on satellites in high orbits, which aren't shielded at all by the Earth's magnetic field. Satellites in lower orbits have problems because of the heating of the atmosphere, which causes more drag on them and can get them spinning slightly, which moves their antennas and solar panels out of alignment.

Another effect is to raise the height of the ionosphere, a belt of electrons that follows the magnetic field of the earth. The ionosphere reflects radio waves, and when the bottom of it rises further from the Earth's surface it allows AM radio stations to broadcast farther. AM Radio guys love this, Kunches said.

But such magnetic disturbances also interfere with radio signals, and can create problems for satellite communications and even cell phone towers at certain times of the day.

The period of maximum activity is scheduled to get more intense through 2013, and then to tail off over the next several months.