UCSD/CASS Center Creates "CAT Scan" of Solar Wind

Center Creates "CAT Scan" of Solar Wind

The San Diego Union - Tribune; San Diego, Calif.
Jeff Ristine

May 6, 2001

They have been called the sun's equivalent of a hurricane: the sudden explosion of a huge bubble of electrified gas from the sun's outer atmosphere.

When these coronal mass ejections reach the Earth's magnetic field, charged particles dumped into the outer atmosphere can disrupt communications systems, damage satellites and interrupt power supplies, even as they trigger the dazzling auroral displays known as the Northern Lights."

Containing billions of tons of material, the geomagnetic storms are easily detected as they leave the sun, but not as they travel through space. To space-weather forecasters, that means advance warnings generally have been a matter of guesswork, with no way to tell whether a mass ejection is going to collide with Earth or go far off to one side.

But at the Center for Astrophysics and Space Sciences at UC San Diego, researchers are using radio telescopes in Japan to bring greater precision to forecasts.

Their work produces what research physicist Bernard V. Jackson calls a CAT scan of the solar wind. Like the medical version that peers at the brain and other inaccessible parts of the body, the result is a 3-D representation of the heliosphere, the bubble of solar wind that emanates from the sun.

Depictions of the coronal mass ejections, which disrupt the solar wind, can be rotated and seen from any perspective. They also project the path of the clouds of particles and magnetic fields hurdling through space at a million miles or more an hour.

"You can actually view the thing before it arrives at Earth," said Jackson, a research physicist who has worked on solar imaging for more than two decades and developed the technique to depict ejections in 3-D.

Since travel time to Earth is usually three or four days, "you can see it a couple days ahead of time . . . and it allows you to say (whether) it's definitely coming toward you," he said. "That's the big key here."

Jackson said the images are made possible by desktop computing power that would have been considered the supercomputer level, and therefore a bit impractical, just a few years ago.

"There are a lot of tools you can observe the sun by, and there's a lot of stuff a spacecraft can observe near Earth," Jackson said. "But in between, it's an awful big space. And if you want to know the details of what's happening, you have to use some sort of remote sensing technique."

Coronagraphs, which create artificial eclipses of the sun, can detect mass ejections as they leave the sun. When placed on spacecraft observatories, the coronagraphs can track the ejections for long distances.

The radio telescopes can't "see" the mass ejections in transit, but rather detect fluctuations in the electron densities of natural radio emissions in the universe.

In the same way that changes in the atmosphere cause stars to twinkle, fluctuations in the intensity of the radio emissions -- measured in fractions of a second -- allow researchers to infer the amount of ejected material that's out there.

And having at least three telescopes in Japan gathering the same data from slightly different perspectives, Jackson said, makes it possible to determine how fast the material is moving and in what direction.

The center sends the data to the National Oceanic and Atmospheric Administration's Space Environment Center in Colorado, which issues periodic alerts on solar activity.

The charged particles don't reach the Earth's surface, so even an early-warning system for mass ejections isn't changing everyday life much -- yet.

But the particles can induce electrical currents that have been known to knock out transformers. And Jackson said the right combination of speed, mass and magnetic field in an ejection might prompt certain precautions.

High-flying aircraft could shift to lower altitudes to avoid irradiation, for instance, or protective measures could be taken for sensitive instruments on spacecraft, which can be damaged by buildups of electrical charge.

Computer programs allowing the 3-D depictions were developed by P. Paul Hick, an assistant research scientist at the Center for Astrophysics and Space Sciences.

"When I was a student, we would look at the sun and take pictures, just look at small features out there," Hick said. "You never really got an idea of how things looked in 3-D."

Picturing the Earth in the middle of a big, complicated shape moving out from the sun "is kind of overwhelming," Hick said. "That idea, of something getting bigger and unfolding like that, it's kind of fascinating just to think about it."

There's no simple version of the 3-D imagery for home computer users, but the UCSD center makes less complicated graphs available on its website:


Updated hourly, its space maps (labeled "synoptic maps" on the Web) use color shading to show the density and velocity of the solar wind passing Earth for the previous few days, along with a two- to three- day forecast.

For related, less technical information on solar activity, try

http://www.spaceweather.com or


The mountaintop radio telescopes UCSD uses to collect data are snowed in for much of the year, and the researchers missed part of an active peak in the 11-year solar cycle during March and the first half of April.

That problem soon may melt away as Jackson and his colleagues move their observation platform into space.

Jackson designed a spacecraft instrument called the Solar Mass Ejection Imager. The instrument was developed with NASA and the U.S. Air Force, and is tentatively scheduled to be launched into Earth orbit in about a year as part of a mission called Coriolis.

Unlike the Japanese radio telescopes, the instrument will function year-round, collect about 10,000 times more data and improve knowledge of the densities of the ejections. One of its primary aims is to better predict geomagnetic disturbances to satellites.

Science Contact:

Bernard Jackson (858) 534-3358