The Sun’s Stealthy Tsunami-Like Blasts of Radiation –How Much of a Threat are They?

Solarflare The Sun can be a potental threat when it sends out powerful solar blasts of radiation towards the Earth. Research shows that one-third of the Sun's blasts are "sneak attacks" that may occur without warning.

"If space weather forecasters rely on some of the traditional danger signs, they'll miss a significant fraction of solar eruptions," said Suli Ma of the Harvard-Smithsonian Center for Astrophysics (CfA).

To reach their conclusion, Ma and her colleagues studied 34 solar eruptions over 8 months using the STEREO spacecraft. STEREO allows us to study the Sun from two different angles simultaneously. It consists of two spacecraft, one ahead of Earth in its orbit and the other trailing behind. The researchers used it to ensure that the events leaving the Sun were definitely on the side facing the Earth.

STEREO is ideal for studying coronal mass ejections, or CMEs. A CME is a huge eruption from the Sun that blasts a billion tons of highly charged particles into space at speeds greater than a million miles per hour. When those charged particles reach Earth, they interact with our planet's magnetic field, potentially creating a geomagnetic storm. Such a storm can interfere with satellite communications, disrupt power grids, or even short out orbiting satellites.

The research found that 11 of the 34 CMEs observed by STEREO were "stealthy," showing none of the usual signals. As a result, any system designed to watch for such warning signs could miss one-third of all solar blasts.

"Meteorologists can give days of warning for a hurricane, but only minutes for a tornado," explained Smithsonian astronomer Leon Golub. "Currently, space weather forecasting is more like tornado warnings. We might know an eruption is imminent, but we can't say exactly when it will happen. And sometimes, they catch us by surprise."

The team continues looking for subtle clues that might allow us to predict an impending "stealth" CME. They caution that their study occurred during a prolonged minimum of solar activity; conditions may change as solar activity increases over the next few years.

"The Sun is entering its stormy season, ramping up toward its next period of maximum activity in 2013 and 2014," said Ma. "The more we learn and understand about it now, the better."

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