Three Rapid Solar Explosions Dazzle
19th Oct 1999
Solar physicists did a double take, then a triple take, last week as the sun produced a rapid-fire series of coronal mass ejections.
The space-based Solar and Heliospheric Observatory (SOHO) captured three dramatic coronal mass ejections (CMEs) in a 14-hour period starting Oct. 12.
The massive solar explosions can carry up to 10 billion tons of plasma traveling as fast as 2000 kilometers per second. And when CMEs collide directly with Earth, they can excite geomagnetic storms that can cause satellite communication failures and disruptions in electric power and radio transmission systems.
But last week's CMEs appeared to expand in tangled loops -- a sign that they weren't heading directly for Earth. Earth-bound CMEs produce "Halo events" -- they loom larger and larger, eventually appearing to envelope the sun itself.
As the sun nears solar maximum, astronomers expect to record at least one CME every day, says David Hathaway, a solar physicist at the NASA/Marshall Space Flight Center.
The solar maximum of the sun's 11-year sunspot cycle is predicted to hit mid-2000. The frequency of the explosions could provide researchers with the information they need to develop a CME forecasting system that would give Earth's electrical based systems advance notice of the disruptions. "The basic cause of CMEs is fairly well understood," says Hathaway. "Like solar flares, they occur whenever there's a rapid, large-scale change in the sun's magnetic field. Solar flares and CMEs often occur together, as they did this weekend, but not necessarily because the flare triggers the CME or vice versa. One can happen without the other and frequently during solar maximum we see CMEs without an associated flare."
SOHO is an international effort of NASA and the European Space Agency.
an emissary solution