Peak of solar maximum on the way – rare type of solar storm sent a barrage of high-energy solar particles
On May 17, 2012 a moderate-sized M-class flare erupted from the Sun and sent out a barrage of high-energy solar particles that belied its initial intensity.
These particles traveled at nearly the speed of light, crossing the 93 million miles between the Sun and Earth in a mere 20 minutes and impacting our atmosphere, causing cascades of neutrons to reach the ground – a rare event known as a ground level enhancement, or GLE. Occasionally (approximately 10-15 times per decade), the Sun emits cosmic rays of sufficient energy and intensity to raise radiation levels on Earth’s surface to the degree that they are readily detected by neutron monitors. Usually scientists would expect this kind of ground level enhancement from a giant coronal mass ejection or a big X-class flare.
This was the first GLE of the current solar cycle – a sure sign that the sun’s regular 11-year cycle is ramping up toward solar maximum.