Two new papers authored by scientists at Boulder’s National Center for Atmospheric Research pose fresh perspectives on the transitions between solar cycles that challenge long-accepted views of the timeline on which one cycle ends and the next one begins.
Heliophysicists have known for a long time that a solar cycle lasts about 11 years, but have had difficulty predicting their transition points. The new research out of NCAR could advance scientists’ understanding of that significantly.
“If the sun repeats what it did over the last 140 years, then we’re heading for the next one in April or May, which means that in my view there’s a lot of models of solar sun spot cycles that are wrong,” said NCAR scientist Scott McIntosh, director of the center’s High Altitude Observatory and who worked on both studies. “A lot of them.”
NCAR scientists in the two papers show how solar cycles suddenly die, potentially causing tsunamis of plasma to roar through the sun’s interior and spark the start of the next solar cycle just a few weeks later.
McIntosh, vacationing in his native Scotland, said in an interview Wednesday the traditional view is that the pivot point from one solar cycle to the next could take a matter of months, or even years.
But the research highlighted in a new paper for which McIntosh is the lead author, “What the Sudden Death of Solar Cycles Can Tell Us About the Nature of the Solar Interior,” published in Solar Physics, suggests the transition from one cycle to the next could take only 28 days, or less, McIntosh said.
He and his partners drew their findings from 140 years’ worth of observations of activity at the sun’s equator, from both ground and space.
Their study, according to a news release, focused on the movement of coronal bright points, flickers of extreme ultraviolet light in the solar atmosphere, which occur even during solar minimum, offering scientists a more complete view of the solar cycle than would be offered by looking only at sunspot activity.
The study enabled scientists to identify what they call “terminator” events that definitively mark the end of a solar cycle. With that knowledge, they predict that the current Solar Cycle 24 will end in the first half of 2020, with the onset of Solar Cycle 25 soon after, according to a news release.
Scientists have long sought a more precise understanding of the timing of what is called solar minimum and solar maximum, because high sunspot activity can affect both Earth’s upper atmosphere, interfering with operations in space, as well as impacting terrestrial power grids, cell phone communications and more.
McIntosh said his team’s work is so challenging of the accepted wisdoms on the timing of solar cycles that it took three years to get the paper through the peer review process and into publication.
The long-accepted models of how the solar cycles behave, he said, have always suggested they are “diffusive,” meaning they evolve slowly.
However, McIntosh’s paper asserts “the transition between sunspot cycles is very, very abrupt. But there is a lot going on in the sun’s interior that we don’t understand, based on those 70-year old models.”
The second new, related paper from NCAR is “Triggering the Birth of New Cycle’s Sunspots by Solar Tsunami,” in Scientific Reports, for which the lead author is Mausumi Dikpati. McIntosh is a contributing author on that paper, which builds on work highlighted in the first paper.
“When will a new cycle’s sunspots appear?” its abstract asks. “We demonstrate a novel physical mechanism, namely that a ‘solar tsunami’ occurring in the sun’s interior shear-fluid layer can trigger new cycle’s magnetic flux emergence at high latitudes, a few weeks after the cessation of old cycles’ flux emergence near the equator.”
In a statement, Dikpati said, “We have observed the sunspot cycle for hundreds of years, but it’s been a mystery what mechanism could transport a signal from the equator, where the cycle ends, to the sun’s mid-latitudes, where the next cycle begins, in such a relatively short amount of time.”
With the expected end next spring to the current solar cycle and the birth of its successor, McIntosh said scientists will have the chance to observe a terminator event as it unfolds. If it arrives as predicted, he said, the results “could revolutionize our understanding of the solar interior and the process that creates sunspots and shape the sunspot cycle.”