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Radio Blackouts Herald Boost in Solar Activity
By Greg Clark
Staff Writer
posted: 02:09 pm ET
17 November 1999
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sunflares_991116Two active solar flares rotating across the face of the sun have caused a string of minor and moderate radio blackouts on Earth the past few days that is expected to continue for at least a week. The flares, which are streams of radiation associated with sunspots, can disturb high frequency radio communications for aviators and mariners for several minutes at a time on the daylight side of Earth, according to forecasters at the National Oceanic and Atmospheric Administration's Space Environment Center. The center tracks solar activity and forecast's the affects solar events may have on Earth. By monitoring data from several solar-observing satellites forecasters issue warnings when the observations indicate that radiation or charged-particle streams might influence Earth. The active flares herald the long-anticipated rise of solar activity on the way to the solar maximum, said Chris Smithtro, a forecaster at the center. The sun's activity, which varies on a roughly 11-year cycle, is expected to peak in March and remain active for the rest of next year. In the past few days no less that 10 events were classified as minor and moderate radio blackouts, Smithtro said. Whereas just a few months ago there might have been one or two such events per month, they are now occurring on a regular basis, he said. "As the frequency increases, the (solar) maximum that we're expecting is finally arriving, so in that sense, its a relief. We've been anticipating this, and it's finally here." Smithtro said forecasters believe most the activity is coming from two solar-flare regions (shown in image below) on the sun that will continue to affect Earth for 7 to 9 days. 
This image of the sun as seen on Nov. 16, 1999 was produced by the Big Bear Solar Observatory. The circles denote the solar flare regions that are the source of radiation that will disturb high-frequency radio transmissions on Earth during the coming week. Once a feature appears on the sun, it takes about 13 days to rotate across the disk, Smithtro said.
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