The biggest flares
Ken Tapping, July 05, 2012
Now that we are keeping an ever-closer eye on the Sun, there are more alarms, often false, about the consequences of the latest things the Sun is throwing in our direction. The most important of these are flares and coronal mass ejections. Flares happen when over hours to days, solar magnetic fields have become stressed to the point where they suddenly snap, arrange themselves more comfortably and release in minutes all the energy stored in them. The result is x-rays, radio waves and high-energy particles that can cause radio blackouts, damage satellite electronics and endanger astronauts and high-altitude air travelers, particularly on polar routes. A coronal mass ejection is less dramatic. A large magnetic loop containing trapped, hot, ionized gas gets more and more stressed until some disturbance makes the magnetic fields snap and the loop, with its contents, gets catapulted into space at speeds of 2000 km/sec or more. These hit our magnetic field and generate magnetic storms, causing power outages, enhanced pipeline corrosion and a lot of other damage. Quite often the shock wave from a flare can trigger a coronal mass ejection, so we often get flares and coronal mass ejections together. This is what happened for example in 1859 and 1989.
For our ancestors, living low-tech existences at ground level, the only things they would have seen to indicate bad solar behaviour were displays of aurora. The only bad consequences would have been indirect, such as watching the aurora and not watching for sabre-toothed tigers or other enemies. Our vulnerability to solar activity comes mainly through its impact on our technology and the complex infrastructure we now depend on. The impact on that infrastructure can be considerable. In 1989 a moderately large solar flare and coronal mass ejection caused about $2 billion worth of damage. In 1859 there was a much bigger flare, which if it happened today would cost us about $2 trillion dollars to put our lives back together. This possibility has triggered work on improving forecasting, warnings and plans to minimize the consequences. However, to answer that question we need to know how big flares might get, and how often the biggest ones to occur. The problem is that we have not been monitoring the Sun for long enough to know. Before the 19th century solar activity had little effect on our activities or us.
However, we can broaden our understanding by looking at stars that are similar to the Sun. There are many of these, and we can monitor these for flares, and determine how often flares of a given size occur. In one study, 83 000 sun-like stars are being monitored. The results so far are intriguing.
A typical large solar flare releases about a million quadrillion joules of energy. Some stars produce “superflares” releasing 100 000 times more energy. However, the most vigorous flares come from stars rotating more quickly than the Sun, which makes it easier to build up a lot of stress in magnetic fields. So it is likely that the Sun won’t be as energetic as that, but basing any conclusions on a century or so of observations of a 4.5 billion-year-old star might be called a bit premature. We’re working on it.
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