These explosions, known as coronal mass ejections (CMEs), lift off from the Sun’s outer atmosphere — the corona, and can cause intense geomagnetic storms, and negatively affect astronauts, satellites, and spacecraft.
CMEs and geomagnetic storms
Geomagnetic storms happen when the Earth’s magnetic field is disturbed. The most extreme geomagnetic storms are driven by CMEs.
CMEs really energize the Earth’s magnetic field, says James Spann, Space Weather Lead at NASA. “The impact of a CME on a magnetized body like the Earth can be very catastrophic depending on its size and speed.”
One of the most intense CMEs is believed to have taken place on September 1, 1859 (the Carrington Event), reaching Earth 17.5 hours later and setting off a large geomagnetic storm. Auroras were seen as far south as the Caribbean and telegraph lines caught fire as communications were disrupted at various locations across the world.
For almost a hundred years, scientists have known that the small to moderate CMEs are more likely to happen when the Sun is more active and producing more sunspots, roughly every 11-years. But there has been some doubt as to whether the most extreme events, like the Carrington Event, also follow the solar cycle.
In a new study, a team of researchers led by Mathew Owens, a space physics professor at the University of Reading in the U.K., have found that the most extreme CMEs are also more likely to occur during peak solar activity.
“These are the ones that we worry about the most, but they appear to be more predictable than once thought,” says Owens.
The researchers looked at 150 years of disturbances to the Earth’s magnetic field and picked out the most extreme CMEs to have occurred and compared them to the solar cycles. Dating back to 1749, we have experienced 24 full solar cycles, with the current solar cycle expected to be in the active phase between 2024 and 2026.
The Carrington Event occurred about six months prior to peak solar activity during cycle 10, which is in line with what we found, and since then there have been approximately six geomagnetic storms that would be considered the most extreme, says Owens.
The effects on terrestrial technology
During a geomagnetic storm, changes in magnetic fields induce currents along power lines that can damage transformers and cause power outages. The most serious event happened on March 13, 1989, and left six million people without power in Québec, Canada for nine hours.
The potential impact on society is far greater today due to the vast extent to which we depend on technology, says Howard Singer, Chief Scientist at the NOAA Space Weather Prediction Center. “The number of technological systems that can be affected by space weather just keeps growing.”
Singer is referring to the 60,000 space weather product subscription registrants, some of whom rely on space weather forecasts and alerts to make informed decisions; for example, deciding when not to schedule power grid maintenance or when flights over polar regions need to be redirected. Space weather can even affect farmers who use technology such as GPS to help make decisions regarding how to best manage crops.
The interconnectedness of technological systems makes society especially vulnerable to large geomagnetic storms, as power outages can disrupt the delivery of essential goods and services. “Extreme events are rare, but when they do happen, we better be ready,” says Singer.
One of the main tools for predicting if a CME is headed towards Earth is the coronagraph— an instrument that blocks out the light from the Sun’s photosphere so that the corona and CME can be observed. The fastest CMEs arrive within a day of lifting off the Sun and can take up to four days to reach Earth.
This Article firstly Publish on astronomy.com