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Three top-tier X-class solar flares launched off the sun between Wednesday and Thursday. The first two occurred seven hours apart, coming in at X1.9 and X1.6 magnitude respectively. The third, the most powerful of the current 11-year "solar cycle," ranked an impressive X6.3. From a report: Solar flares, or bursts of radiation, are ranked on a scale that goes from A, B and C to M and X, in increasing order of intensity. They usually originate from sunspots, or bruiselike discolorations on the surface of the sun. Sunspots are most common near the height of the 11-year solar cycle. The current cycle, number 25, is expected to reach its peak this year. The more sunspots, the more opportunities for solar flares.
Solar flares and accompanying coronal mass ejections, or CMEs, can influence "space weather" across the solar system, and even here on Earth. CMEs are slower shock waves of magnetic energy from the sun. Flares can reach Earth in minutes, but CMEs usually take at least a day. All three of the X-class solar flares disrupted shortwave radio communications on Earth. But the first two flares did not release a CME; the verdict is still out regarding whether the third flare did. High-frequency radio waves propagate by bouncing off electrons in Earth's ionosphere. That's a layer of Earth's atmosphere between 50 and 600 miles above the ground.
When a solar flare occurs, that radiation travels toward Earth at the speed of light. It can ionize additional particles in the lower ionosphere. Radio waves sent from devices below it then impact that extra-ionized layer and lose energy, and aren't able to be bent by ions at the top of the ionosphere. That means signals can't travel very far, and radio blackouts are possible. Three back-to-back radio blackouts occurred in response to the trio of flares, but primarily over the Pacific and Indian oceans. They were rated "R3" or greater on a 1 through 5 scale. According to the National Oceanic and Atmospheric Administration's Space Weather Prediction Center, that results in a "wide area blackout of [high frequency] radio communication, [and] loss of radio contact for about an hour on sunlit side of Earth." Low-frequency navigation signals, like those used on aircraft traveling overseas, can be degraded too.
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