A solar flare erupted from a departing sunspot on September 16, releasing a pulse of X-rays and extreme UV radiation which caused a shortwave radio blackout in Africa and the Middle East. Frequencies below 25 MHz were affected for up to an hour after the flare.
Solar flare strength is measured much like the Richter scale which measures earthquakes. Solar flares are classed A, B, C, M or X where each successive letter corresponds to a 10-fold increase in energy output. A-class solar flares are barely above background radiation emission from the sun.
Spaceweather.com reports that the September 16 solar flare, exploding out of sunspot AR3098, was an M8-class, meaning it was nearly an X-flare, the most powerful kind.
According the UK Met Office Space Weather division, the radio blackout was a “moderate” category R2 (R1 is minor, R5 is extreme) event.
Space weather experts believe that the solar flare could be accompanied by a coronal mass ejection (CME) from the sun’s coronasphere (a shell of million-degree plasma which extends millions of kilometres from the sun’s surface). According to the Met and other space weather forecasters, the CME might cause G1-level (minor) geomagnetic instability over the coming days, resulting in weak power grid fluctuations and minor impact on satellite operations.
But, as we become increasingly reliant on technology and satellites which are less protected from solar activity, such events could spell danger.
This was highlighted on February 4 when 38 of SpaceX’s “Starlink” satellites began falling out of the sky due to a “minor” G1-class geomagnetic storm. SpaceX’s Starlink is a satellite internet constellation aimed at providing internet access to 40 countries and global mobile phone service after 2023.
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An M1-class solar flare triggered a CME and geomagnetic storm. A paper published in the Space Weather journal explains how a seemingly “minor” storm could cause so much damage.
“Although it was only ‘minor,’ the storm pumped almost 1200 gigawatts of energy into Earth’s atmosphere,” explains lead author Tong Dang, from China’s University of Science and Technology. “This extra energy heated Earth’s upper atmosphere and sharply increased aerodynamic drag on the satellites.”
Of the 49 Starlink satellites crowded into the Falcon 9 rocket which launched on February 3, only a quarter survived. The project was given a boost last week when SpaceX launched another Falcon 9 rocket with new Starlink satellites.
The satellites will be stationed in a higher orbit in an attempt to mitigate the atmospheric effects which led to the Starlink mess from earlier in the year.
While solar flares are notoriously difficult (impossible) to predict, scientists warn that powerful flares are going to be more common as the sun enters Solar Cycle 25 and sunspot activity is expected to peak in 2025.
Solar cycles average 11 years in length and have been tracked since Solar Cycle 1 was described in 1755.
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The greatest solar flare incident of the last 500 years occurred about 160 years ago.
On September 1, 1859, Richard Carrington, one of England’s foremost solar astronomers was observing sunspots. While sketching what he saw, Carrington saw two beads of blinding white light appear over the sunspots.
Before dawn the next day, skies all over the planet were bathed in red, green and purple auroras including in the Caribbean. Telegraph systems were disrupted, and their operators electrocuted, setting telegraph papers on fire.
The incident went down in history as the “Carrington Event” and scientists believe that the solar flare was around an X45-class flare, making it the most powerful in recorded history.
Other more recent events involving X-class solar flares show how damaging they can be.
In 1972, a solar flare knocked out long-distance telephone communication across the US. A 1989 solar flare left six million Canadians without power for nine hours. And in 2000, an X5-class solar flare on Bastille Day caused some satellites to short circuit and led to radio blackouts.
As the solar cycle reaches its maximum, space weather scientists warn that things are getting pretty rowdy. In fact, the sun has already been more active than predicted this cycle and there have been several X-class flares unleashed so far this year.
Science Alert reports that we can expect more geomagnetic storms as the cycle reaches its peak, including moderate and strong storms. Strong storms would see a disruption of satellites and navigation systems.
Evrim Yazgin has a Bachelor of Science majoring in mathematical physics and a Master of Science in physics, both from the University of Melbourne.
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