A geomagnetic superstorm is one of the most extreme forms of space weather, created when the Sun sends enormous bursts of energy and charged particles toward Earth. These powerful events rarely occur, typically appearing only once every 20-25 years. On May 10-11, 2024, Earth was hit by the strongest event of this kind in more than two decades, known as the Gannon storm or Mother's Day storm.
A research effort led by Dr. Atsuki Shinbori of Nagoya University's Institute for Space-Earth Environmental Research gathered direct observations during the storm and produced the first detailed view of how such an event squeezes Earth's plasmasphere (a protective region of charged particles surrounding the planet). The results, published in Earth, Planets and Space, show how both the plasmasphere and the ionosphere respond during intense solar disturbances and offer insight that can improve predictions of satellite disruptions, GPS problems, and communication issues caused by extreme space weather.
Arase Satellite Captures a Rare Plasmasphere Collapse
Launched by the Japan Aerospace Exploration Agency (JAXA) in 2016, the Arase satellite travels through Earth's plasmasphere and measures plasma waves and magnetic fields. During the May 2024 superstorm, it happened to be in an ideal position to record the severe compression of the plasmasphere and the long, slow recovery that followed. This marked the first time scientists had continuous, direct data showing the plasmasphere contracting to such a low altitude during a superstorm.
"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.
Superstorm Pushes Plasmasphere to Record-Low Altitudes
The plasmasphere works with Earth's magnetic field to help block harmful charged particles from the Sun and deep space, offering natural protection for satellites and other technology. Under normal conditions, this region stretches far from Earth, but the May storm forced its outer edge inward from about 44,000 km above the surface to only 9,600 km.
The storm formed after several major eruptions on the Sun released billions of tons of charged particles toward Earth. Within just nine hours, the plasmasphere was compressed to roughly one-fifth of its usual size. Its recovery was unusually slow, requiring more than four days to refill, which is the longest recovery time recorded since Arase began monitoring the region in 2017.
"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," Dr. Shinbori noted.
Superstorm Pushes Auroras Farther Toward the Equator
During the peak of the storm, the Sun's activity compressed Earth's magnetic field so strongly that charged particles were able to travel much farther along magnetic field lines toward the equator. As a result, vivid auroras appeared in places that rarely experience them.
Auroras normally occur near the poles because Earth's magnetic field channels solar particles into the atmosphere there. This storm was powerful enough to shift the auroral zone far beyond its usual location near the Arctic and Antarctic circles, producing displays in mid-latitude regions such as Japan, Mexico, and southern Europe -- areas where auroras are seldom seen. Stronger geomagnetic storms allow the lights to reach increasingly equatorial regions.
Negative Storms Slow the Plasmasphere's Return to Normal
About an hour after the superstorm arrived, charged particles surged through Earth's upper atmosphere at high latitudes and flowed toward the polar cap. As the storm weakened, the plasmasphere began to replenish with particles supplied by the ionosphere.
This refill process usually takes only a day or two, but in this case the recovery stretched out to four days because of a phenomenon known as a negative storm. In a negative storm, particle levels in the ionosphere drop sharply over large areas when intense heating alters atmospheric chemistry. This reduces oxygen ions that help create hydrogen particles needed to restore the plasmasphere. Negative storms are invisible and can only be detected using satellites.
"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," Dr. Shinbori said.
Why These Findings Matter for Space Weather and Technology
These results provide a clearer understanding of how the plasmasphere changes during a severe solar storm and how energy moves through this region of space. Several satellites experienced electrical problems or stopped transmitting data during the event, GPS signals became less accurate, and radio communications were disrupted. Knowing how long Earth's plasma layer takes to recover from such disturbances is essential for predicting future space weather and for protecting the technology that relies on stable conditions in near-Earth space.
