S Shape May Help Predict Solar Storms.

Space scientists are calling it the other Y2K problem.

Sometime next year, the sun is expected to reach the peak of its 11-year activity cycle. For the next several years, this volatile cauldron of gas will have more frequent temper tantrums than usual. As the sun continues to rage, it will hurl more magnetized clouds of electrically charged gas into space.

Some of these solar storms, known as coronal mass ejections, may wreak havoc if they plow into the magnetic cocoon surrounding Earth. The blobs of solar material sometimes induce large electric currents on Earth, harming satellites and knocking out power grids (SN: 3/6/99, p. 150). Researchers reported this week that they have uncovered an important clue that may help them predict many of these storms hours to days before the sun spews them out. Once it erupts, an outburst takes about 4 days to reach Earth.

After analyzing daily X-ray images taken over 2 years by a Japanese-U.S.-British satellite called Yohkoh, Richard C. Canfield of Montana State University in Bozeman and his collaborators found that S marks the spot. Within active regions on the sun--places that show intense magnetic activity--those areas that exhibit an S-shaped pattern in their X-ray emissions are the ones most likely to erupt.

"We've found that the S-shaped regions are the dangerous ones," he says.

Found in the sun's outer atmosphere, or corona, the S's are believed to trace the tightly twisted, helical magnetic fields that power many solar outbursts.

The new study follows up on a 1998 report by Hugh S. Hudson, based at the Institute of Space and Astronautical Science in Sagamihara, Japan, and Alphonse Sterling of Computational Physics in Fairfax, Va. They found indications that some coronal mass ejections correlate with an S pattern. The new analysis puts that preliminary finding on a surer statistical footing, Canfield notes.

He announced the findings at a NASA press briefing in Washington, D.C. Canfield, Hudson, and David E. McKenzie of Montana State also describe their results in the March 15 GEOPHYSICAL RESEARCH LETTERS.

Planetary scientists do not yet know how soon after the appearance of an S pattern an active region will erupt. Moreover, the S shape does not indicate the speed and direction of a coronal mass ejection or the orientation of its magnetic field. Such information is critical for forecasting which of the many solar eruptions could pose a danger to our planet (SN: 2/1/97, p. 68).

Nonetheless, the new findings "are a harbinger of great things to come," says Ernest Hildner, director of the National Oceanic and Atmospheric Administration's Space Environment Center (SEC) in Boulder, Colo. "This is a potential milestone," says his SEC colleague Joseph Hirman.

Hildner says that he's excited about the results because computers can be trained to recognize the S pattern in solar images and to track regions that show the telltale shape. A successor to Yohkoh's instruments, a device installed on a weather satellite scheduled for launch in 2001, will generate an X-ray image of the sun every minute, he notes. Scanning the multitude of pictures for an S pattern could prove invaluable for forecasting geomagnetic storms, Hildner says.

Canfield notes that not all coronal mass ejections are associated with the S pattern, and J.T. Gosling of the Los Alamos (N.M.) National Laboratory points out that not all outbursts come from active regions. Canfield and his team "have a decent result, but we've not completely understood what produces coronal mass ejections, by a long shot," says Gosling.