On Friday night, May 10, 2024, an enormous G5 solar storm struck planet Earth after five coronal mass ejections (CMEs) moving at varying speeds through the solar system converged over the planet. The aurora borealis was observed all across North America, with reports as far south as Florida, Hawai’i, Mexico, and even the Caribbean. The aurora also visited California, where onlookers in the Angeles National Forest above the marine layer we able to observe pillars of red light to the north. A Kp Index of about 8.67 or higher is needed to observe the aurora borealis with the naked eye at 34° latitude and reduced light pollution.
How does it work?
The sun goes through 11-year cycles of sunspot activity that can observed over decades by satellite instrumentation. When sunspot activity peaks, a phenomena known as a coronal mass ejections (CMEs) can occur several times per Earth day. When the 11-year cycle bottoms out, days or even weeks can pass without any CMEs from the sun.
Since the sun spins, it creates its own magnetic field just like Earth. The insides of the sun are so hot and pressurized that the magnetic field lines within the sun can become tangled up and kinked. When they kink, excess energy can get trapped in small area, and this excess energy will push outward towards the sun’s surface. If it is strong enough, it’ll blast through the sun’s surface in a massive explosion that can become larger than the planet Jupiter in a matter of minutes. These explosions are called coronal mass ejections, or CMEs for short. In the process, positively charged protons get blasted out into outer space.
A coronal mass ejection (CME) also sends out a magnetic flux, which are shockwaves in the magnetic field. Combined with the charged protons, the two will race off into space at anywhere between 1,000,000 MPH and 5,000,000 MPH in velocity depending on how severe the CME was. Once the CMEs leave the surface of the sun, they are called solar storms. Solar storms can overwhelm the Earth’s magnetic field and excite gasses in the upper atmosphere. This process is what causes the aurora.
On Wednesday morning, May 8th at around 8:00 UTC, two CMEs ejected from the sun and began racing right towards planet Earth. Later in the day Wednesday, another two average-strength CMEs exploded from the sun, also headed in the Earth’s direction. Finally, on Thursday morning, an extremely powerful CME occurred moving much faster than the rest. When CMEs leave the sun, an entire quarter of the solar system can be impacted, so it isn’t unusual for any planet to be hit by one. What was unusual this time, however, was that all 5 CMEs converged simultaneously over planet Earth leading to what is now the strongest solar storm of the generation. This animation from the University of Reading shows what multiple solar storms converging over the Earth (black dot) looks like:
Solar storms of this magnitude have a return period of about once every 20 years. What made Friday’s event so special was that it occurred during a new moon which helped lower light levels. Additionally, a marine cloud deck in place over the coastal valleys drastically lowered light pollution in upper Eaton Canyon.
A mad rush to Mount Wilson on Saturday night by thousands of spectators hoping to catch a glimpse did not yield any result, as the solar storm had already passed. Indeed, Friday night was the only night to view the northern lights in Los Angeles County.
“The aurora borealis was a no show up from Mt. Wilson tonight [Saturday]. It was a rowdy scene, and if I had known it would be so insanely attended, I would have probably stayed home. When we finally did get out it was a funeral procession of hundreds of cars the entire way down [the Angeles Crest Highway.]”
– Facebook user
Here are some photographs of the event in and around upper Eaton Canyon:
