Last July 14, the sun spewed a billion-ton cloud of high-energy particles, traveling at nearly 4 million mph, toward Earth. This was not a unique event; it has been known for years that the sun undergoes a periodic increase and decrease in activity after an 11-year cycle.

Observers found that the numbers of sunspots, and their distance from the solar equator, could be used as an indicator of both the intensity of solar activity and when it might be expected to peak. The reason for this connection became clearer in 1908, when American astronomer George Hale found a link between sunspots and intense magnetic field activity on the sun.

In 1960, this link was explained by another American astronomer, Horace Babcock, who said that the sun produces intense magnetic lines of force by rotation of electrically charged gases that break the surface of the sun in great loops. Sunspots are cool regions where these loops protrude through the surface.

As the sun rotates, these lines of force become tangled and twisted, storing huge amounts of energy. Finally, when the strain becomes too great, the loops snap, releasing the energy in a gigantic explosion. This may be either in the form of a solar flare, which is a massive burst of radiation, or a coronal mass ejection, or CME, sending millions of tons of high-energy, ionized particles speeding to Earth.

The July 14 CME was not unique or even particularly large in comparison to past eruptions. It is changes on Earth, and not on the sun, that have made solar storms of particular concern today.

Ron Cowen explains why we are now particularly vulnerable to the sun’s eruptions in the Jan. 13 issue of Science News. There are now more than 2,000 communication and research satellites orbiting in the path of the CMEs that have been launched during the last two solar cycles. These are particularly vulnerable to high-energy electrons that pierce their skins and cause sparking in delicate electronics.

In the current solar cycle, NASA’s SOHO and Chandra research satellites were damaged, a Japanese X-ray satellite was reduced to another piece of orbiting space junk, and a communications satellite, Galaxy IV, was completely fried, causing 45 million pagers to go dead.

Power grids are also at risk. No major disruptions have occurred during this cycle, but at the height of the last one, in 1989, a Hydro-Quebec grid was completely overwhelmed by a CME, plunging the entire province into darkness.

Solar researchers predict storms as severe as the July one over the next two years, and, since power is being transmitted over greater distances without sufficient devices to regulate voltage surges, one says, “power grids are more vulnerable today than they were 10 years ago.”

Today scientists have a flotilla of eight spacecraft and satellites at their disposal to predict the likelihood of a solar storm.

Despite all the data flowing back to them, solar physicist Craig DeForest admits that “if weather predictions were as bad as our ability to predict solar storms, we’d fire all the weathermen.”

What they can do is monitor the sun’s activity and spot a CME on its way to Earth. One satellite, a million miles out in space, can give an hour’s advance warning before the storm of ionized particles reaches the fleet of orbiting satellites.

This allows time to shut down their vulnerable electronics before they are destroyed. However, the primary purpose of the flotilla is to study the physics of solar eruptions and their effect on Earth.

One unsuspected effect of solar storms now coming to light, writes Sid Perkins in the Jan. 20 issue of Science News, is on the Earth’s climate. During a solar eruption, it is possible for the Earth to receive more than five times the ultraviolet radiation than it does normally.

This causes a significant temperature increase in the upper atmosphere but much less at the surface; however, some researchers believe it may play a minor role in global warming.

Most of the data come from isolated studies, and no one has proposed a mechanism to link weather and climate to solar activity.

British climatologist Peter Stott has developed an elaborate computer model comparing the global average temperatures since 1850 to effects from both human activity and natural causes. Stott says that, when both of these are factored out, there remains a small warming effect that can be attributed to the 11-year solar cycle. Others dismiss the claim, saying, “The effect is no more than a faint signal in a noisy system.”

Much remains to be done before we fully understand how the sun affects our planet and our lives.

Clair Wood taught chemistry and physics for more than 10 years at Eastern Maine Technical College in Bangor.