On Mother’s Day weekend in May 2024, Earth was struck by one of the most powerful geomagnetic storms in recent decades, turning night skies across the planet into brilliant curtains of green, red and purple light. Auroras were reported unusually far from the polar regions, appearing over places including Mississippi, northern Italy, the Himalayas and Queensland, Australia. Now, a new study suggests that the spectacle was powered by an exceptionally complex chain of solar eruptions: not one or two coronal mass ejections, but 10 separate blasts that merged and accelerated as they traveled toward Earth.
Coronal mass ejections, or CMEs, are immense clouds of magnetized plasma expelled from the sun’s outer atmosphere. They can contain billions of tons of charged particles and travel through interplanetary space at hundreds or even thousands of miles per second. When a CME reaches Earth, its magnetic field can interact with the planet’s magnetosphere, the protective region shaped by Earth’s own magnetic field. If the incoming magnetic field is oriented favorably, it can transfer large amounts of energy into near-Earth space, triggering a geomagnetic storm and driving charged particles toward the upper atmosphere, where they produce auroras.
The May 2024 event was already considered extraordinary. It occurred during solar maximum, the most active phase of the sun’s approximately 11-year magnetic cycle, when sunspots, flares and CMEs become more frequent. The resulting storm reached a level not seen in roughly two decades, and some scientists suggested that the associated auroral display may have been among the strongest observed in the past 500 years. The new analysis, led by space physicists at the University of Iowa, provides a detailed explanation for why the storm became so powerful.
Researchers determined that the eruptions occurred over a period of four days. The first seven CMEs interacted and merged as they moved away from the sun, creating a much larger and more coherent magnetic structure. Two additional eruptions later combined with each other before catching up with the already consolidated cloud. Finally, a tenth CME launched at an extraordinary speed of nearly 1,000 miles per second and slammed into the expanding structure, compressing and pushing it toward Earth.
The result was not simply a series of separate solar storms arriving one after another. Instead, the eruptions behaved like a turbulent convoy in space, with later, faster clouds overtaking earlier ones. As the CMEs collided, their magnetic fields and plasma interacted, producing a larger and more energetic compound structure. This process, known as CME interaction or cannibalism, can alter the speed, density and magnetic orientation of the resulting cloud, making its effects at Earth difficult to predict using models designed for isolated eruptions.
Evidence for the event came from NASA’s Wind spacecraft, which measures the solar wind near the point where it encounters Earth’s magnetic environment. The solar wind is a continuous flow of charged particles from the sun, but it is often dramatically disturbed by CMEs. Wind recorded four magnetic clouds passing the spacecraft, leading scientists initially to suspect that only a small number of eruptions had reached Earth. However, the researchers noticed that the solar wind following the clouds was moving at more than twice its typical speed. That unusually fast flow suggested that additional eruptions had been hidden within the larger, interacting structure.
To reconstruct the full sequence, the team combined spacecraft observations with magnetohydrodynamic, or MHD, modeling. MHD simulations describe the behavior of electrically conducting fluids such as solar plasma while accounting for magnetic fields. By modeling the sun’s surface activity and the propagation of the eruptions through interplanetary space, the researchers were able to reproduce the observations recorded near Earth. Their simulations indicated that 10 CMEs were needed to explain the timing, speed and magnetic structure of the material that ultimately struck the planet.
“This was unique,” says Shirsh Soni, a postdoctoral research fellow in the University of Iowa’s Department of Physics and Astronomy and the study’s corresponding author. According to the researchers, no previous event had been documented with current observational and simulation techniques in which 10 CMEs erupted and merged into a single, Earth-directed disturbance. The findings show that the largest geomagnetic storms may be shaped not only by the properties of an individual CME, but also by the history of its interactions with other eruptions during its journey.
The discovery has important implications for space-weather forecasting. Strong geomagnetic storms can produce spectacular auroras, but they can also disrupt satellite operations, radio communications, navigation systems and electrical infrastructure. In May 2024, the storm prompted concerns about satellite drag and technological systems operating in space and on the ground. “Most of the space weather models we have are for individual eruptions,” Soni explains. The researchers argue that future forecasting systems must account for multiple CMEs, their collisions and the way later eruptions can recharge or reshape a magnetic cloud before it reaches Earth.
The study, titled “Comprehensive MHD modelling of ten successive CMEs driving a historic geomagnetic storm — the 2024 Mother’s Day event,” was published in The Astrophysical Journal. Its authors say that understanding how solar eruptions merge could provide earlier and more reliable warnings before the sun’s next major outburst arrives. The sun is expected to move eventually into a quieter phase of its activity cycle, but solar maximum will return. When it does, the lessons of the Mother’s Day storm could help scientists determine whether a seemingly ordinary eruption is actually part of a much larger and faster-moving solar superstorm.
Subject of Research: Solar coronal mass ejections and geomagnetic storms
Article Title: Comprehensive MHD modelling of ten successive CMEs driving a historic geomagnetic storm — the 2024 Mother’s Day event
News Publication Date: 7-Aug-2026
Web References: NASA’s Wind mission: https://wind.nasa.gov/ ; NASA overview of the May 2024 solar storm: https://science.nasa.gov/science-research/heliophysics/how-nasa-tracked-the-most-intense-solar-storm-in-decades/ ; Shirsh Soni, University of Iowa: https://physics.uiowa.edu/people/shirsh-lata-soni
References: The Astrophysical Journal; Shirsh Soni, Anwesha Maharana, Sanchita Pal and Stefaan Poedts
Image Credits: Shirsh Soni, University of Iowa
Keywords
Solar storm, coronal mass ejection, geomagnetic storm, aurora, space weather, solar maximum, magnetosphere, solar plasma, MHD modeling, NASA Wind
