A powerful solar flare spat out from the sun sparked radio blackouts across South America and the mid-Atlantic Ocean on Saturday.
The sunspot responsible for the "very strong" X4.5-class flare-named sunspot AR3825-also ejected a large plume of solar plasma, which is headed in the direction of Earth.
When this coronal mass ejection (CME) hits the atmosphere, it is expected to spark G3-class geomagnetic storms, leading to the northern lights being visible as far south as California, Missouri and Colorado, according to spaceweather.com.
Solar flares and CMEs occur when the magnetic energy built up in the sun's atmosphere is suddenly released, usually near sunspots. Solar flares are powerful bursts of radiation-including X-rays and ultraviolet (UV) light emanating from the sun-while CMEs are enormous chunks of solar plasma and magnetic field.
The radiation from solar flares can cause radio blackouts because of their impact on Earth's ionosphere, which is a layer of the atmosphere filled with charged particles. This layer is important for communication, as it reflects high-frequency radio waves, allowing long-distance communications. Increased intensity of X-rays and UV radiation causes a surge in ionization in the ionosphere, which causes the ionosphere to absorb high-frequency radio waves rather than reflecting them, resulting in radio signals degrading or completely fading out.
"The Earth's ionosphere is a region of our atmosphere between 80 and 600 km above the Earth's surface. The ionosphere is very sensitive to X-rays from the sun and during a flare, X-rays can light up the ionosphere, causing a so-called ionospheric disturbance," Peter T. Gallagher, a professor of astronomy and astrophysics at the Dublin Institute for Advanced Studies in Ireland, told Newsweek.
"The ionosphere is used in radio-based communications to reflect or allow the transmission of radio waves, but radio communications can be blacked out when the ionosphere is disturbed by X-rays from a solar flare."
The September 14 radio blackout resulted in ham radio operators and mariners seeing a loss of signal at frequencies below 30 MHz for as long as a half-hour.
The strength of the solar flare determines the extent of the blackout. Flares are classified into categories ranging between A, B, C, M and X, with X the most powerful. At X4.5, this weekend's flare was one of the most powerful forms. The most powerful flare ever recorded was detected in 2003, and estimated to be about X45.
The CME released at the same time as the X4.5 flare is heading toward Earth and is expected to hit our magnetic field later Monday.
"Periods of G3 [Strong] geomagnetic storms are likely on 16 Sep 2024 due to coronal hole influences and the anticipated arrival of a CME associated with an X4.5 flare at 14/1529 UTC from AR3825," NOAA's Space Weather Prediction Center said in a forecast. "Aurora may be visible as low as Pennsylvania to Iowa to Oregon."
Geomagnetic storms are categorized on a scale of G1 to G5, with G5 storms the most powerful and most uncommon. The G5 storm that caused auroras to be seen across much of the U.S. on May 10 was the first since 2003, during the same storms that sparked the X45 flare.
Charged particles in the CME are funneled by Earth's magnetic field toward the polar regions, where they interact with gases like oxygen and nitrogen, causing light emissions known as the aurora. More powerful geomagnetic storms result in auroras being seen at much lower latitudes than usual. The auroras take on different colors depending on the type of gas involved in the collisions, with oxygen usually giving off green or red light, while nitrogen can produce blue or purplish hues.