Millions of people around the world were treated to a brilliant display of aurora lights this week. The Sun produced at least five major "halo" coronal mass ejections (CMEs) over the period of Nov. 4-8, an unusually fast pace for solar activity.
A "halo" CME occurs when a CME produces an expanding circle of particles all around the Sun. When observers see this they know the CME is heading directly towards or away from Earth. In this case, all were headed in our direction, bringing the auroral light show with them. The source of storms was a group of sunspots called Active Region 696. The area also produced powerful solar explosions called flares.
The most significant solar storm occurred late on Nov. 5th (Universal Time). The aurora, also known as the Northern and Southern Lights, form when solar particles and magnetic fields pump energy into the Earth's magnetic field, accelerating electrically charged particles trapped within. The high-speed particles crash into Earth's upper atmosphere (ionosphere) over the polar regions, causing the atmosphere to emit a ghostly, multicolored glow. More solar storms may well impact Earth at least for several more days.
This kind of solar activity is getting increasingly rare as we enter into the quiet period of the Sun's eleven-year cycle of activity. The years 2000-2001 marked the highest point of activity, but that doesn't preclude the occasional surprise like this week's CMEs. Even more significant were the intense solar storms that raged about a year ago.
Check out the Space Weather site for more aurora predictions or the Space Weather section of the SOHO web site for more observations.
Steele Hill & Rachel A. Weintraub
NASA Goddard Space Flight Center