The sun experiences seasonal changes, study finds

Brett Smith for redOrbit.com – @ParkstBrett

Our sun goes through a few activity cycles and a new study has identified one such cycle that is almost seasonal in nature.

According to the report, published in the journal Nature Communications, the nearly two-year cycle appears to be caused by shifts in the bands of powerful magnetic fields in each solar hemisphere. These bands also aid in shaping and approximately 11-year solar cycle that is part of a lengthier cycle that lasts approximately 22 years.

“What we’re looking at here is a massive driver of solar storms,” said study author Scott McIntosh, director of the High Altitude Observatory at the National Center for Atmospheric Research (NCAR). “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.”

Two overlapping parallel bands

The new study is one of a number of papers by the same study team that examines the affect of the magnetic bands on many connected cycles of solar magnetism. In a paper published last year, the authors indicated that the approximately 11-year sunspot cycle is driven by two overlapping parallel bands of reverse magnetic polarity that slowly move over nearly 22 years from high solar latitudes toward the equator, where they meet and dissipate.

The team recognized the twisted, ring-shaped stripes by using on a number of NASA satellites and ground-based assets that collect data on the structure of the Sun, the nature of solar flares and coronal mass ejections (CMEs). These findings exposed the bands in the form of variances in the density of magnetic fuel that went up from the solar interior, through transition area known as the tachocline and on to the surface, where they associated with shifts in flares and CMEs.

In the new study, the researchers determined that the migrating rings generate seasonal variations in solar activity that are as robust as those seen in the more familiar 11-year counterpart cycle. These seasonal variants take place individually in both the northern and southern halves of the Sun.

“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 study author Robert Leamon, a solar physicist at Montana State University.

The newly-found variability also explains why powerful solar flares and CMEs often peak a year or more after the maximum number of sunspots. Based on the study findings, the answer seems to be that seasonal changes cause an uptick in solar disruptions long after the peak in the solar cycle.

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