The Sun can lash the Earth with powerful winds that can disrupt communications, aviation and power lines even when it is in the quiet phase of its 11-year solar cycle, say US scientists.
Observers have traditionally used the number of sunspots on the surface of the Sun to measure its activity. The number of sunspots reaches a peak at what is called the solar maximum and then declines to reach a minimum during a cycle.
At the peak, intense solar flares and geomagnetic storms eject vast amounts of energy into space, crashing into the Earth’s protective magnetic fields, knocking out satellites, disrupting communications and causing colourful aurora.
But scientists at the National Center for Atmospheric Research in the United States and the University of Michigan found that the Earth was bombarded with intense solar winds last year despite an unusually quiet phase for the Sun.
“The Sun continues to surprise us,” says Dr Sarah Gibson of the Center’s High Altitude Observatory and lead author of the study. “The solar wind can hit Earth like a fire hose even when there are virtually no sunspots.”
Scientists previously thought the streams of energy largely disappeared as the solar cycle approached the minimum.