Plasmasphere compressed by recent geomagnetic superstorm dramatically slowed recovery

by Riko Seibo
Tokyo, Japan (SPX) Nov 21, 2025

Researchers have detailed how a geomagnetic superstorm on May 10-11, 2024, shrank Earth's plasmasphere, a protective zone of charged particles, to just one-fifth of its normal size. The event, named the Gannon storm or Mother's Day storm, was the most powerful in over twenty years.

Led by Dr. Atsuki Shinbori at Nagoya University's Institute for Space-Earth Environmental Research, the team used data from the Arase satellite, which was ideally positioned to observe the plasmasphere's compression and subsequent slow recovery. This provided the first direct, continuous measurements of the shrinking plasmasphere during such an intense storm.

"We tracked changes in the plasmasphere using the Arase satellite and used ground-based GPS receivers to monitor the ionosphere-the source of charged particles that refill the plasmasphere. Monitoring both layers showed us how dramatically the plasmasphere contracted and why recovery took so long," Dr. Shinbori explained.

The results showed that the outer edge of the plasmasphere dropped from roughly 44,000 km to just 9,600 km above Earth's surface within nine hours. The plasmasphere took more than four days to return to normal, a much lengthier recovery period than observed since Arase began its mission in 2017.

Dr. Shinbori noted, "We found that the storm first caused intense heating near the poles, but later this led to a big drop in charged particles across the ionosphere, which slowed recovery. This prolonged disruption can affect GPS accuracy, interfere with satellite operations, and complicate space weather forecasting."

Auroras appeared at unusually low latitudes as the compressed magnetic field allowed particles to reach areas closer to the equator, including Japan, Mexico, and southern Europe. Typically, auroras are restricted to polar regions, but the strength of the Gannon storm enabled them to be visible much farther south than usual.

The study also documents a 'negative storm' phase, when particle levels in the ionosphere dropped sharply and hindered the plasmasphere's refill. According to Dr. Shinbori, "The negative storm slowed recovery by altering atmospheric chemistry and cutting off the supply of particles to the plasmasphere. This link between negative storms and delayed recovery had never been clearly observed before."

The findings have implications for understanding how energy and particles move during solar storms and for improving forecasts that protect satellites and communications infrastructure. Several satellites experienced electrical problems, GPS outages occurred, and radio links were disrupted during the event.

Research Report:Characteristics of temporal and spatial variation of the electron density in the plasmasphere and ionosphere during the May 2024 super geomagnetic storm