Astronomy By Bruce Dorminey | Published: Tuesday, August 20, 2019
Strange behavior may hide deeper meanings within our star.Solar observers have been on a wild ride over the past decade, painstakingly trying to make sense of our yellow dwarf star’s increasingly puzzling sunspot cycles — or, rather, the lack of such cycles.
The Sun is supposed to follow 11-year cycles of minimum and maximum activity that should trace set patterns pretty much like clockwork, give or take weaker and stronger sunspot patterns, flares, and periods of coronal mass ejections. But solar cycle 24, which began in 2008, and the predictions for cycle 25, which will commence in 2020, take the cake for anomalous behavior.
The sunspot maximum of cycle 24, which began almost a year late, looks to be the smallest in 100 years and the third in a trend of diminishing activity within sunspot cycles. So, cycle 25 likely could be smaller than cycle 24.
Predicting a quiet future
“The leading [solar polar magnetic field] indicator in use for solar cycle 25 shows that the next cycle will be similar to the current one,†says astrophysicist Dean Pesnell of NASA’s Goddard Space Flight Center in Maryland. “This indicator has been accurate for the last four cycles.†Unfortunately, astronomers cannot accurately forecast the level of solar activity much past the next maximum, Pesnell says. He notes that the internal process that recycles and amplifies the magnetic field still is not well understood.
This peculiar solar behavior raises questions for astronomers. Does the previous cycle hint at what the Sun has in store in the future? What can we expect for the next two or three solar cycles? Is Earth destined for a colder climate rather than a warmer climate? And could our idea about our own spectral type G2 star’s peculiar midlife behavior need tweaking or even be flawed?
Cycle 24 is one of the weakest sunspot and magnetic activity cycles in more than a century, says Edward Guinan, an astronomer at Villanova University. Cycle 24 (and probably cycle 25) could be part of a suggested 100-year cycle that appears in the solar sunspot record known as the Gleissberg Cycle, he says. “Analysis of trends and magnetic field strengths does indicate that the upcoming sunspot minimum will be very low, and [cycle 25] will also be about the same or even at lower activity than the current one,†says Guinan.
Without a predictive theory for the solar dynamo — the physical process that generates the Sun’s magnetic fields — it isn’t clear what we might expect for the next few cycles, says Mark Giampapa, deputy director of the National Solar Observatory (NSO) in Tucson, Arizona. “Right now, the subsurface flow fields would seem to indicate that cycle 25 will be even weaker than the current cycle, with fewer than 100 spots,†he says.
However, David Hathaway, an astrophysicist at NASA’s Ames Research Center, says cycles tend to grow bigger and bigger over five to six cycles and then become smaller and smaller over the following five to six cycles. He notes that the Sun is currently in a phase of declining activity.
More:
http://astronomy.com/magazine/2019/08/why-has-the-sun-gone-quiet
