High energy explosions on the sun's surface Friday sent streams of radioactive particles into Earth's atmosphere that may disrupt communications systems and ultimately cause auroras to glow at the poles.

Solar flares of this magnitude have not been detected since 1984, and only 10 flares equally spectacular were detected in the past 11-year sunspot cycle that ended in 1986.Scientists who recorded the activity believe the flares occurred as part of a new cycle of sunspots that are pockmarking the face of the giant star in a region that expands an estimated 50,000 to 100,000 miles.

"These flares are unusually large and certainly will be causing some disturbances on the Earth," said astrophysicist Dale Gary of the California Institute of Technology. He expects such low-frequency shortwave communications systems as ham radio operations to be especially affected.

Solar flares also pose dangers for astronauts, but Gary expects the two Soviet cosmonauts now orbiting Earth to be protected from high energy particles because "they are shielded by Earth's magnetosphere and the metal of the spacecraft itself," he said.

"When flares occur, especially like these with lots of X-ray emissions, the X-rays arrive at the Earth as soon as the flares occur," he said.

Satellite communications whose signals beam through the outer layer of Earth's atmosphere, called the ionosphere, also will undergo disturbances because the particles from the solar explosions depress the layer, he said.

"This is the beginning of a new (unspot) cycle and indications are that this one will be quite large. It's getting off to a rather big start," Gary said.

The flares erupted Friday in a region of the sun that had undergone on Thursday what Gary described as "flux." The solar flares are expected to be followed by magnetic storms that will dump energetic protons into Earth's atmosphere within 24 to 48 hours of the explosions.

"When these particles hit the upper atmosphere, they will cause it to glow," he said.

That bombardment is expected to affect Earth's North and South poles in the form of colorful auroras, which should be visible from the northeast regions of the United States, he said.

"Solar flares are very much associated with sunspots especially in the complex regions that give the most spots. Sunspots occur in groups and we call those groups active regions," he said.

Because sunspots occur in 11-year cycles, scientists can trace their evolution. Solar regions with high magnetic activity have been associated with sunspots, which are generally cooler than other areas of the sun.