Solar Flare: Radio Blackouts Hit US

A sunspot on the surface of our volatile star exploded yesterday, sending an extremely powerful solar flare flashing through space towards the Earth.

The flare, which hit an X7.1-class in strength, is the second-strongest solar flare we have seen so far this solar cycle, and sparked shortwave radio blackouts over Hawaii and the Pacific Ocean.

The explosion from sunspot AR3842 also resulted in a large plume of solar plasma—also known as a coronal mass ejection, or CME—being flung in our direction.

This may trigger geomagnetic storms when it arrives on October 5, according to preliminary NASA modeling.

Solar flares are immensely powerful flashes of X-rays and ultraviolet radiation that occur in areas of the sun where the magnetic fields are especially strong and complex, typically around sunspots.

The sun goes through an 11-year solar cycle of magnetic activity, with the solar maximum being the period in the cycle when the sun is at its most active, resulting in an increased number of sunspots, solar flares, and CMEs.

“There is a whole range of solar flare sizes, with large solar flares really only happening around solar maximum. Sunspots and therefore solar flares come and go over an 11-year cycle of activity, with the next maximum predicted to occur in mid-2025,” Peter T. Gallagher, a professor of astronomy and astrophysics at the Dublin Institute for Advanced Studies in Ireland, told Newsweek.

Solar flares are ranked between A, B, C, M and X, with each class being ten times more powerful than the previous one. X-class flares are the most powerful and most rare, and can cause more severe impacts to Earth.

At an X7.1-class, this flare was the second-most powerful of this solar cycle—Solar Cycle 25—so far, after the X8.7 flare on May 14 this year.

This most recent flare is the 25th most powerful since 1996, while the May flare was the 17th most powerful. The top 5 most powerful flares all occurred around the maximum of Solar Cycle 23, with November 2003 seeing an X40+ flare.

Powerful solar flares can result in widespread radio blackouts, long-lasting radiation storms, and damage to satellites, spacecraft, and even power grids on Earth.

These radio blackouts are caused due to solar flares’ effects on the Earth’s ionosphere, which is filled with charged particles that reflect radio signals around the planet, playing a key role in radio transmission.

During a solar flare, the intense X-rays and UV radiation increase the ionization levels in this region, causing it to start absorbing high-frequency radio waves, especially those in the HF band, or 3 to 30 MHz. This absorption leads to a sudden loss of signal, causing radio blackouts, particularly on the side of the Earth facing the sun.

The CME associated with this recent flare is expected to arrive at our planet on October 5, though the degree to which it will collide with our magnetic field and how strong it will be is yet to be determined.

If powerful enough, however, it could trigger geomagnetic storms and spark the northern lights being seen across the U.S.

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about solar flares? Let us know via science@newsweek.com.