Nagoya University-led study finds Earth's atmosphere dominated particles in May 2024 geomagnetic storm

During the May 10 and 11, 2024 solar superstorm, a chain of eruptions from a large sunspot sent magnetized plasma toward Earth. The combined plasma clouds struck the magnetosphere and drove the SYM-H geomagnetic index to -518 nanotesla, the second-largest recorded disturbance since 1981. A Nagoya University-led team reported that the storm also produced the strongest magnetic disturbance ever measured in Earth's ring current, a belt of charged particles circling the planet thousands of kilometers above the equator.

The evidence comes from direct satellite measurements of ring-current composition during an extreme geomagnetic storm, a measurement the study describes as unprecedented for a disturbance of this size. Scientists compared signatures of ions from the solar wind with ions lifted from Earth's ionosphere, the charged upper atmosphere. They found solar-wind particles contributed very little, while atmospheric ions dominated the current. The study design is a single-event satellite measurement campaign, effectively a sample size of one extreme storm; its key limitation is that it captures one storm, not a population of storms.

For decades, scientists have debated whether ring-current particles come mainly from the solar wind or Earth's ionosphere, with both known to contribute during storms. The May 2024 result challenges the expectation that an especially dense solar wind would keep solar particles important in an extreme event. Because atmospheric ions such as oxygen are heavier than solar-wind hydrogen, they may have helped intensify the magnetic disturbance and pushed the ring current unusually close to Earth. The finding reframes geomagnetic storms as interactions between space weather and Earth's own atmosphere.

The stakes are practical because extreme geomagnetic storms can endanger spacecraft, disturb GPS and communications, and induce currents that affect power grids. The source says some super or extreme storms are not just impressive light shows but pose radiation risks and can cause power outages. The finding identifies Earth's atmospheric ions as a physical input that storm models need to represent, alongside solar-wind forecasts, when assessing how severe a geomagnetic disturbance may become. It also strengthens the case for a proposed Japanese satellite mission to study how atmospheric particles enter space and influence storms.