Warning for solar flares

Microwave bursts may serve as warning shots

IGUASSU FALLS, Brazil — Fluctuating bursts of microwave energy from the sun could provide imminent warning of the huge solar flares known as coronal mass ejections, new research hints.

During periods of intense solar activity, immense clouds of radiation and charged particles erupt from the sun’s surface. When these coronal mass ejections, or CMEs, strike and envelope Earth, they can disrupt radio communications, overload power grids and zap Earth-orbiting satellites, Pierre Kaufmann, a solar physicist at Mackenzie Presbyterian University in Sao Paulo, Brazil, reported August 9 at the Meeting of the Americas.

When Kaufmann and colleague Rodney V. Souza recently studied the solar emissions associated with 10 CMEs that occurred during an intense period of solar activity in October and November 2003, they noticed that the sun emitted bursts of microwave energy during or before each one. For three of the CMEs, the burst coincided with the flares’ eruptions from the sun’s surface. But for the other seven, the microwave bursts — which fluctuated every few seconds — preceded the eruption of the CME by between five and 15 minutes.

Kaufmann and his colleagues are now expanding their study to determine how often microwave bursts occur without a subsequent CME. If bursts that aren’t ultimately linked to CMEs turn out to be rare, the emissions could serve as a warning that a CME will soon follow.

The largest fraction of charged particles from a CME reaches Earth between several hours and a couple of days after leaving the sun. But some of the most energetic — and therefore the most potentially damaging — particles travel at half the speed of light and reach Earth in just minutes, said Dalmiro J. Maia, a solar physicist at the University of Porto in Portugal.

Even a warning that comes minutes before a CME’s eruption could help engineers prevent damage to satellites or other equipment, Maia said. Early warnings would be especially useful for protecting probes orbiting Mercury or Venus, which would be struck by clouds of charged particles more quickly than Earth would.

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