The sun has been blank for 21 straight days–a remarkable 3 weeks without sunspots. This is an almost decade-class event. The last time the sun lost its spots for 21 consecutive days was in the year 2009 coming on the heels of an historic solar minimum. With the current stretch of blank suns, solar minimum conditions have definitely returned.
To find an equal stretch of spotless suns in the historical record, you have to go back to July-August 2009 when the sun was emerging from a century-class solar minimum. We are now entering a new solar minimum, possibly as deep as the last one.
Solar minimum is a normal part of the solar cycle. Every 11 years or so, sunspot production sputters. Dark cores that produce solar flares and CMEs vanish from the solar disk, leaving the sun blank for long stretches of time. These quiet spells have been coming with regularity since the sunspot cycle was discovered in 1859.
However, not all solar minima are alike. The last one in 2008-2009 surprised observers with its depth and side-effects. Sunspot counts dropped to a 100-year low; the sun dimmed by 0.1%; Earth’s upper atmosphere collapsed, allowing space junk to accumulate; and the pressure of the solar wind flaggedwhile cosmic rays (normally repelled by solar wind) surged to Space Age highs. These events upended the orthodox picture of solar minimum as “uneventful.”
Space weather forecasters have long wondered, will the next solar minimum (2018-2020) be as deep as the previous one (2008-2009)? Twenty-one days without sunspots is not enough to answer that question. During the solar minimum of 2008-2009, the longest unbroken interval of spotlessness was ~52 days, adding to a total of 813 intermittent spotless days observed throughout the multi-year minimum. The corresponding totals now are only 21days and 244 days, respectively. If this solar minimum is like the last one, we still have a long way to go.
How does this affect us on Earth? Contrary to popular belief, auroras do not vanish during solar minimum. Instead, they retreat to polar regions and may change color. Arctic sky watchers can still count on good displays this autumn and winter as streams of solar wind buffet Earth’s magnetic field. The biggest change brought by solar minimum may be cosmic rays. High energy particles from deep space penetrate the inner solar system with greater ease during periods of low solar activity. NASA spacecraft and space weather balloons are already detecting an increase in radiation. Cosmic rays alter the flow of electricity through Earth’s atmosphere, trigger lightning, potentially alter cloud cover, and dose commercial air travelers with extra “rads on a plane.”
At the moment there are no nascent sunspots on the solar disk, so the spotless days counter is likely to keep ticking.
Via NASA Spaceweather.com