Solar Cycles End with 'Terminator' Events That Herald New Era of Activity on Sun, Studies Say

"Terminator" events appear to mark the end of the Sun's solar cycles—and potentially trigger the next wave of activity on the surface of our star. These discoveries could provide a better understanding into how the solar cycles work and potentially predict them with more accuracy than is currently possible.

The Sun is known to go through cycles that last around 11 years, during which the magnetic field flips. Over this time, sunspot activity—where temporary dark patches appear on its surface—goes up and down. The solar maximum is where activity peaks, while the solar minimum is marked by fewer sunspots.

The solar maximum is also associated with increased coronal mass ejections and high-energy solar flares. If these events are directed towards Earth, it can impact our planet by interrupting systems that rely on GPS, knocking out power grids and disrupting satellite communication systems. At present, the Sun is coming to the end of Solar Cycle 24, with the National Oceanic and Atmospheric Administration (NOAA) predicts the next solar maximum will take place between 2023 and 2026.

In two studies, researchers have discovered a mechanism that appears to mark the end of one solar cycle and the beginning of the next.

In one paper, published in the journal Solar Physics, researchers led by Scott McIntosh from the National Center for Atmospheric Research looked at 140 years worth of observations of the Sun. They found "terminator events" that appear to be closely linked to the magnetic activity that takes place at the start of the Sun's magnetic reversals.

"These 'terminator' events appear to be very closely related to the onset of magnetic activity belonging to the next solar cycle at mid-latitudes and the polar-reversal process at high latitudes," they wrote.

In another paper published in Scientific Reports, a team led by Mausumi Dikpati, also from the National Center for Atmospheric Research, looked at the mechanism behind terminator events. Findings suggest there is a "solar tsunami" that takes place in the Sun's interior, with fluid rushing towards the equator where it cannot be contained. The fluid then propagates towards the poles at a speed of around 300 meters per second. When it hits the mid-latitudes, where the sunspot-producing fields are, it triggers surface eruptions that lead to the new solar cycle.

They say that more research will be needed to understand how solar tsunamis work, with simulations to show the different hemispheres, as well as a better understanding of the "observational 'signatures' of the triggering of a new cycle."

However, they conclude: "The next tsunami is due by 2020, portending the start of intense 'space weather' that can adversely impact the Earth."

The NOAA predicts the next solar cycle will be weak, much like Solar Cycle 24 has been. "While we are not predicting a particularly active Solar Cycle 25, violent eruptions from the sun can occur at any time," Doug Biesecker, a solar physicist at NOAA's Space Weather Prediction Center, said in a statement released April.

sunspot
A giant sunspot erupting on the surface of the Sun in 2014. NASA Goddard
Solar Cycles End with 'Terminator' Events That Herald New Era of Activity on Sun, Studies Say | Tech & Science