Between March 6 and March 21, the surface of the sun was devoid of the sunspot regions that normally sweep across it while the sun rotates.
The 15-day spotless streak was the longest in “many years”, NASA said. Sunspot regions can be points of reference for those watching the sun. Without them, NASA said, “any viewer would have a hard time telling that the sun was even rotating.”
The sunspot-free streak ended Wednesday, noted SpaceWeather.com.
The present absence of sunspots is happening as their overall numbers decline in the sun’s approach to its next “solar minimum,” when its irradiance or brightness reaches its lowest contemporary levels, which happens in about an 11-year cycle.
The last period of sunspot activity this low occurred in April 2010, near the previous solar minimum, wrote meteorologist Paul Dorian, who operates the website and blog Vencore Weather.
“There have already been 26 spotless days in 2017 (34 percent of the entire year) and this follows 32 spotless days last year which occurred primarily during the latter part of the year,” he wrote. “The blank look to the sun will increase in frequency over the next couple of years leading up to the next solar minimum — probably to be reached in late 2019 or 2020.”
During the progression toward solar minimum, the sun is conducting some large-scale housekeeping. It is shedding magnetic fields from the previous cycle as it stops making spots. Then, some years later, it will begin manufacturing new spots at high latitudes, with opposite polarity, marking the start of the next solar cycle.
At the moment, even in its spotless state, the sun still has faculae (Latin for little torch), or bright regions, on its disc, explained Judith Lean, a solar physicist at the U.S. Naval Observatory. “It means even though the sunspots have gone, the sun’s irradiance isn’t yet at its minimal level,” Lean said. Once the solar minimum is reached, both sunspots and faculae will reach low points.
Does the lack of sunspots have significance for weather and climate? “I would say no,” Lean said. “It’s not something somebody’s going to notice. The response time of climate system to changes in solar irradiance are longer than days and probably longer than months. It takes time for there to be a response to a change in the energy input to the climate system.”
Lean added that even the difference in the sun’s brightness between the solar minimum and maximum has a “modest” effect on the climate compared to things such as greenhouse gases.
Space weather will change markedly with the disappearance of spots and the diminished solar magnetic fields. Solar flares and coronal mass ejections, which are plumes of plasma unleashed by the sun, will be ever-so-rare, and the “weather” will generally be tranquil. However, it’s worth noting that even though solar storms become much less frequent toward the solar minimum, occurrences of strong, eruptive fields still do occur, but for short spates from rogue sunspot groups.
Even as space weather generally calms, “space climate” will have an increase in its main threat to Earth systems and, in some cases, travelers. Near the solar minimum, galactic cosmic rays from distant supernovae more easily penetrate our solar system, compared to the solar maximum. The downside of these rays is increased radiation affecting satellites, astronauts and even high-altitude, high-latitude airplanes. This constant “drizzle” will nag some applications for the next five or so years.