RELEASE NO: 97-169

Using spacecraft and supercomputers, scientists from the International Solar Terrestrial Physics (ISTP) program have developed a new theory for the explosive, high velocity coronal mass ejections (CMEs) that will erupt from the Sun with increasing frequency during the maximum of the new solar cycle. CMEs are eruptions of electrically charged gas from the Sun that can trigger magnetic storms around Earth. Such storms occasionally disturb spacecraft, navigation and communications systems, and electric power grids.

Recent experimental and theoretical observations from ISTP indicate that the interaction of magnetic fields high above the Sun’s surface allows tremendous energy to build up and to release CMEs at speeds approaching 1,250 miles per second (2,000 kilometer per second). In other announcements, scientists have determined that "halo" CMEs almost always lead to geomagnetic storms, an observation of great consequence for the prediction of space weather. Finally, ISTP researchers have been able to create realistic computer simulations of the effects that CMEs can have on Earth's magnetic field.

ISTP scientists will present this research at a press conference at 9 a.m. PST on Monday, Dec. 8 in San Francisco’s Moscone Center during the Fall Meeting of the American Geophysical Union.

Coronal mass ejections are the largest structures that erupt from the Sun. Most CMEs travel at 250 miles per second (400 kilometers per second), but "fast" CMEs can reach speeds double or triple that. Fast CMEs can accelerate atomic particles called protons in interplanetary space to the point where they can harm spacecraft. The first fast CME of the new solar cycle was observed on Nov. 6, 1997. Slow or fast, the eruptions produce magnetic clouds that can cause geomagnetic storms and increase the intensity of the aurora (Northern and Southern lights).

Inspired by images of CMEs collected by the Large Angle Spectrometric Coronograph on the SOHO spacecraft, Dr. Spiro Antiochos of the U.S. Naval Research Laboratory in Washington, D.C., has proposed a new answer to the long-standing question of how the Sun can build up the energy to produce the violent explosions of fast CMEs. Using supercomputers from NASA and the Department of Defense, Antiochos has

created a model that simulates the complex, interwoven magnetic structures of the Sun. After observing how magnetic fields abut and interact, Antiochos theorizes that the Sun’s magnetic fields tend to restrain each other and force the buildup of tremendous energy.

Eventually, through a process known as "magnetic reconnection" --where opposing magnetic lines of force merge and cancel -- the field is released from its bonds and escapes the Sun as high speed.

Antiochos compares the process to that of filling a helium balloon. "If you fill it without anchoring it, the balloon will slowly drift upward," he said. "But if you hold the balloon down as you fill it, you can generate a lot of upward force, which makes the balloon take off at higher speed once you release it. Fast CMEs are released in the same way."

In other research, ISTP teams headed by David Webb of Boston College and the Research Laboratory at Hanscom Air Force Base and by Dr. Guenter Brueckner of the Naval Research Laboratory studied nine "halo" type CMEs that occurred from December 1996 to May 1997. They found that such events almost always result in magnetic activity at Earth. Halo CMEs are so named because they appear as expanding halos around the Sun when seen from the perspective of Earth.

According to Dr. Nancy Crooker, a space physicist at Boston University, detection of halo events will vastly improve methods of predicting geomagnetic storms. "If you see a halo CME, you are pretty sure that you are going to see a storm at Earth," Crooker said. "In the past, scientists could only look at solar flares to know if a storm was heading towards Earth. And while some flares have accompanying CMEs, some don’t. But now we have instruments sensitive enough to see the CMEs themselves."

ISTP does not predict space weather. Forecasting is the domain of the Space Environment Center of the National Oceanic and Atmospheric Administration.

Crooker and Webb also have identified the signature of halo CMEs on the Sun's surface. These remnants of CMEs show up in X rays and ultraviolet light as the sudden brightening of magnetic arches, with dimming areas on either side. These dimming areas seem to mark the roots of CMEs already launched into space.

Downwind from those eruptions, the invisible magnetic shell (or magnetosphere) that shields Earth from the Sun’s particles and radiation is regularly shaped and shorn by CMEs. To better understand this interaction, Dr. Charles Goodrich, of the University of Maryland, has developed a series of animations that depict how the magnetosphere responds to the shock of a CME.

Using a Cray C-90 and other powerful computers, Goodrich and colleagues have for the first time depicted the evolution of the magnetosphere as it is bombarded by a real CME. The simulation reconstructs the arrival of CME on Jan. 10-11, 1997, an event that produced magnetic storms and spectacular auroral displays, and poured as much as 1,400 Gigawatts of electricity into the atmosphere (almost double the power generating capacity of the United States).

"This is a global picture of what is going on in the magnetosphere," said Goodrich. "Since we only have a few spacecraft, and they can only make point measurements, this is the only way to look at the whole system."

Information about ISTP and the physics of the Sun and Earth may be found at URL: http://www-istp.gsfc.nasa.gov/istp/outreach/frontpage.html .

NOTE TO EDITORS: Images to support this story can be found at the following internet location: http://www.gsfc.nasa.gov/ftp/newsmedia/AGU_ISTP/ . A video file to support this story will be broadcast on NASA TV Dec. 8.