As the sun moves through its 11-year cycle, it experiences active and quiet periods known as the solar maximum and solar minimum.
While solar maximum can present itself in a host of different ways, a new study has found that microwaves emitted during the solar minimum have largely remained the same for more than half a century.
The discovery is surprising, the researchers say, and could help to provide a clearer understanding of the processes that give rise to sunspots and other solar activity.
While solar maximum can present itself in a host of different ways, a new study has found that microwaves emitted during the solar minimum have largely remained the same for more than half a century. Researchers analyzed data going back to 1957, as illustrated above
THE SOLAR CYCLE
Conventional wisdom holds that solar activity swings back and forth like a simple pendulum.
At one end of the cycle, there is a quiet time with few sunspots and flares.
At the other end, solar max brings high sunspot numbers and frequent solar storms.
It’s a regular rhythm that repeats every 11 years.
Reality is more complicated.
Astronomers have been counting sunspots for centuries, and they have seen that the solar cycle is not perfectly regular.
Astronomers in Japan have been continuously monitoring solar microwaves across four-frequencies since 1957.
This began at the Toyokawa Branch of the Research Institute of Atmospherics, Nagoya University, and was later relocated in 1994 to the NAOj Nobeyama Campus.
In a new study, researchers analyzed the solar microwave data collected during the telescopes’ six decade observation, revealing that the microwave intensities and spectra for solar minimum were the same every time in the last five cycles.
The solar maximums, however, varied in both intensity and spectrum from cycle to cycle.
‘Other than sunspot observations, uniform long-term observations are rare in solar astronomy,’ says lead researcher Masumi Shimojo.
‘It is very meaningful to discover a trend extending beyond a single solar cycle. This is an important step in understanding the creation and amplification of solar magnetic fields, which generate sunspots and other solar activity.’
NASA recently revealed that the sun is heading toward solar minimum.
In this time, certain types of activity, such as sunspots and solar flares will drop – but, it’s also expected to bring the development of long-lived phenomena including coronal holes.
According to NASA, solar minimum could also enhance the effects of space weather, potentially disrupting communications and navigation systems, and even causing space junk to ‘hang around.’
The sun is heading into a period known as solar minimum, during which activity at the surface will ‘change form.’ While sunspots were relatively high back in 2014, they’re now heading toward a low point expected in 2019-2020, according to NASA
The sun follows roughly an 11-year cycle. While sunspots were relatively high back in 2014, they’re now heading toward a low point expected in 2019-2020, according to NASA.
‘This is called solar minimum,’ said Dean Pesnell of NASA’s Goddard Space Flight Center in Greenbelt, MD. ‘And it’s a regular part of the sunspot cycle.’
The change, however, doesn’t mean that activity ceases altogether, the expert explains.
Instead, different types of events tend to take hold.
For instance, ‘during solar minimum we can see the development of long-lived coronal holes,’ Pesnell says.
‘We see these holes throughout the solar cycle, but during solar minimum, they can last for a long time – six months or more.’
These are areas in the sun’s atmosphere where the magnetic field opens up, sending streams of solar particles into space.
HOW SOLAR WIND IS FORMED
The sun and its atmosphere are made of plasma – a mix of positively and negatively charged particles which have separated at extremely high temperatures, that both carries and travels along magnetic field lines.
Material from the corona streams out into space, filling the solar system with the solar wind.
But scientists found that as the plasma travels further away from the sun, things change.
The sun begins to lose magnetic control, forming the boundary that defines the outer corona – the very edge of the sun.
The breakup of the rays is similar to the way water shoots out from a squirt gun.
First, the water is a smooth and unified stream, but it eventually breaks up into droplets, then smaller drops and eventually a fine, misty spray.
A recent Nasa study captured the plasma at the same stage where a stream of water gradually disintegrates into droplets.
If charged particles from solar winds hit Earth’s magnectic field, this can cause problems for satellite and communication equipment.
When the resulting solar wind hits Earth’s magnetic field, it can cause space weather events including geomagnetic storms, auroras, and disruptions to communications and even satellites.
According to NASA, it can even effect the space debris floating around Earth.
The drag experienced as objects circle Earth helps to keep low-Earth orbit clean, the space agency explains.
This is the result of heating by ultraviolet radiation from the sun.
When solar minimum occurs, the upper atmosphere cools down, reducing the drag.
And, NASA explains, this means space junk is more likely to linger.
‘During solar minimum, the sun’s magnetic field weakens and provides less shielding from these cosmic rays,’ Pesnell says.
‘This can pose an increased threat to astronauts travelling through space.’