Everyone knows Earth has seasons, dictated by the planet’s relationship with the Sun. Now, scientists have discovered that the Sun experiences its own seasonal fluctuations, according to a study by the National Center for Atmospheric Research (NCAR). The fluctuations, which ebb and flow over the Sun’s 11-year cycles, may help scientists on Earth predict when solar storms will be stronger or weaker.
“What we’re looking at here is a massive driver of solar storms,” said Scott McIntosh, lead author of the new study and director of NCAR’s High Altitude Observatory. “By better understanding how these activity bands form in the Sun and cause seasonal instabilities, there’s the potential to greatly improve forecasts of space weather events.”
The Sun’s seasons are a bit longer than Earth’s, playing out over approximately two-year periods. The variations are the result of bands of strong magnetic fields, kind of like the Sun’s version of the Jet Stream. Those bands control activity during the 11-year cycle, which is actually part of a longer 22-year cycle.
The fluctuations in the bands are fueled by rotation of the Sun’s core, causing activity to peak over the course of about 11 months, before winding back down over a similar interval.
“Much like Earth’s jet stream, whose warps and waves have had severe impact on our regional weather patterns in the past couple of winters, the bands on the Sun have very slow-moving waves that can expand and warp it too,” said co-author Robert Leamon, a scientist at Montana State University. “Sometimes this results in magnetic fields leaking from one band to the other. In other cases, the warp drags magnetic fields from deep in the solar interior, near the tachocline, and pushes them toward the surface.”
When magnetic energy from the Sun’s interior surges outward, the destabilization of the Sun’s corona is what’s responsible for most high-intensity solar storms, which can have a significant impact here on Earth.
Scientists arrived at their conclusions by drawing on data from myriad satellites that observe the Sun, and those same satellites will be useful in observing and understanding the Sun’s seasonal changes. New satellites could be commissioned, and satellites already monitoring weather on Earth could be re-purposed to observe the seasonal changes in the Sun.
“If you understand what the patterns of solar activity are telling you, you’ll know whether we’re in the stormy phase or the quiet phase in each hemisphere,” McIntosh said. “If we can combine these pieces of information, forecast skill goes through the roof.”