The sun is an enigma for humans. The star is in an active state sometimes, while there is a lull in its activity at other intervals.
The star, which is in the middle of its 11-year long cycle (Solar Cycle 25), is witnessing a surge in activities currently.
In the last week only, it exuded three solar flares, 18 coronal mass ejections, and one geomagnetic storm, as per India Today.
As the sun nears its peak of the solar cycle, which is likely to happen in 2025, there will be a rise in sunspots. Sunspots are ‘dark, planet-sized regions’ that appear on the sun’s surface. They are cooler than other parts of the Sun’s surface, and hence appear dark.
Moreover, solar flares and coronal mass ejections (giant eruptions on the sun) also increase during the solar cycle. “These eruptions send powerful bursts of energy and material into space,” which can have effects on the earth, as per the National Aeronautics and Space Administration (NASA).
However, there are times when the sunspots disappear completely making the sun ‘quiet’.
What happens when the sun goes quiet? Let’s take a closer look.
Does the sun sleep?
Dubbed as ‘grand minima’, the quiet phase of the sun is marked by a decline in solar radiation and particulate output, notes India Today.
During the 11-year solar cycle, the sun’s powerful magnetic field undergoes changes affecting the amount of activity on its surface.
At the end of the cycle, the magnetic field turns turtle which means the sun’s north and south poles switch places.
Even though we know what happens to the sun’s surface during the quiet period, there is not much information about its polar and interior regions.
The Indian researchers have shed some light on this.
Indian researchers’ study
Center of Excellence in Space Sciences researchers at the Indian Institute of Science Education and Research (IISER), Kolkata have revealed what happens when there is a lull in the sun’s activities.
The study published in the journal Monthly Notices of the Royal Astronomical Society has found that when the sun appears to be ‘asleep’ there are still ‘churnings in the polar and interior regions’, reports India Today.
The internal dynamo mechanism of the 4.6 billion-year-old sun also continues to work during these quiet periods.
The research conducted by IISER PhD student Chitradeep Saha, Sanghita Chandra and Professor Dibyendu Nandy has discovered that the magnetic fields in the sun’s interior continue to operate during the quiet period, as per India Today.
There is ‘gradual decay’ of the polar field during solar grand minima periods, finds the study.
“Our 10,000-year-long computer simulations shed light on the dynamics that go on in the solar interior (convection zone) and at the polar regions even when there are critically low number of sunspot eruptions on the solar surface for a prolonged period known as grand solar minimum. The ceaseless plasma motion and turbulent fluctuations in the convection zone eventually help the star regain its regular magnetic activity again,” Chitradeep Saha, lead author of the paper told India Today.
Grand solar minimum
During the grand solar minimum, the usual 11-year solar cycle is impacted leading to virtually no sunspots on the star for several decades, reports New Scientist magazine.
The reduced solar activity during the previous Cycle 24 has sparked concern among the experts that in the next few decades we could reach the grand solar minimum.
Cycle 24 was one of the ‘weakest sunspot and magnetic activity cycles in more than a century’, Edward Guinan, an astronomer at Villanova University, told Astronomy magazine.
“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,” Guinan added.
Known as the Maunder minimum, the last grand minimum occurred from 1645 to 1715 when the sunspot activity reduced drastically.
It coincided with the worst European winters of the ‘little ice age’ in the Northern Hemisphere, according to New Scientist.
However, experts say the solar minimum would not result in another ice age again.
“The warming caused by the greenhouse gas emissions from the human burning of fossil fuels is six times greater than the possible decades-long cooling from a prolonged grand solar minimum,” says NASA’s Global Climate Change blog.
The Sun goes through regular cycles of high & low activity. This cycle affects the frequency of space weather events, but it doesn’t have a major effect on Earth’s climate — even an extended minimum wouldn’t have a significant effect on global temperature. https://t.co/t2Fw58ZBVt
— NASA Sun & Space (@NASASun) May 18, 2020
“Even if a grand solar minimum were to last a century, global temperatures would continue to warm. Because more factors than just variations in the sun’s output change global temperatures on earth, the most dominant of those today being the warming coming from human-induced greenhouse gas emissions,” NASA stated.
With inputs from agencies
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