The May 2024 geomagnetic superstorm provided scientists with an unprecedented opportunity to observe Earth's protective plasma shield collapsing in real time.
Japan's Arase satellite, positioned perfectly in orbit during the Mother's Day storm, captured the first continuous direct measurements of the plasmasphere shrinking to one-fifth its normal size.
This historic dataset from JAXA's mission revealed why the recovery process stretched to more than four days, far exceeding typical timelines.
Researchers from Nagoya University's Institute for Space-Earth Environmental Research, led by Dr. Atsuki Shinbori, published their findings in Earth, Planets and Space after analyzing data from the strongest geomagnetic event in over 20 years.
The study combines satellite observations with ground-based GPS measurements to explain how both the plasmasphere and ionosphere responded during extreme solar activity, offering critical insights for protecting satellites, navigation systems, and communication networks from future space weather events.
How Did the Arase Satellite Witness This Historic Event
Launched by the Japan Aerospace Exploration Agency in December 2016, the Arase satellite orbits through Earth's plasmasphere, measuring plasma waves and magnetic fields with nine specialized scientific instruments.
During the superstorm on May 10 and 11, 2024, the satellite happened to be positioned ideally to record the dramatic compression and exceptionally slow recovery of the plasmasphere.
Previous storms lacked this level of continuous direct observation at such low altitudes during peak intensity.
The spacecraft travels in an elliptical orbit with an apogee of about 32,000 kilometers, passing directly through the region where the plasmasphere boundary collapsed during the storm.
This orbital path allowed Arase to measure plasma density, temperature, and electromagnetic waves continuously as the protective layer contracted and then gradually rebuilt.
Scientists combined this satellite data with measurements from more than 5,800 ground-based GPS receivers worldwide to track ionospheric changes that affected the plasmasphere's recovery rate.
Did you know?
Over a period of approximately 100,000 years, Earth's orbit transitions from being nearly a perfect circle (low eccentricity) to a more stretched-out oval (high eccentricity) and back again.
What Caused the Plasmasphere to Shrink by 80 Percent
The plasmasphere normally extends from about 1,000 kilometers above Earth's surface to approximately 44,000 kilometers into space, forming a protective barrier of cold dense plasma trapped by Earth's magnetic field.
During the Mother's Day superstorm, a series of powerful coronal mass ejections from the Sun launched billions of tons of charged particles toward our planet at speeds exceeding 1,000 kilometers per second.
When this solar material collided with Earth's magnetosphere, it compressed the magnetic field lines and forced the plasmasphere's outer boundary inward.
In just nine hours, the plasmasphere contracted from its typical 44,000-kilometer radius down to only 9,600 kilometers above Earth's surface.
This represented an 80 percent reduction in the protective layer's normal extent, exposing satellites in medium Earth orbit to higher levels of energetic particles and radiation.
The compression occurred as the storm injected intense energy into the magnetosphere, creating electric fields that pushed plasma away from the equatorial region and temporarily disrupted the delicate balance maintaining the plasmasphere's structure.
Why Did Recovery Take Four Days Instead of Two
Under normal circumstances, the plasmasphere refills within one to two days after a geomagnetic storm subsides, as charged particles from the ionosphere flow upward along magnetic field lines to replenish the depleted region.
However, Arase's measurements revealed that recovery from the May 2024 superstorm required more than four days, the longest refilling period documented since the satellite began operations in 2017.
The culprit behind this extended timeline was a phenomenon called a negative ionospheric storm.
Dr. Shinbori's team discovered that approximately one hour after the storm began, intense heating near Earth's poles altered the upper atmosphere's chemical composition.
This heating decreased the ratio between atomic oxygen and molecular nitrogen, which in turn reduced the production of oxygen ions that normally generate hydrogen particles needed to refill the plasmasphere.
The negative storm created a widespread depletion of charged particles across the ionosphere, essentially cutting off the supply of material that would flow upward to restore the plasmasphere to its pre-storm configuration.
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What Made Auroras Appear at Such Low Latitudes
Auroras typically occur within narrow bands near the Arctic and Antarctic circles, roughly 60 to 70 degrees latitude, where Earth's magnetic field guides solar particles into the upper atmosphere.
During the May 2024 superstorm, however, spectacular auroral displays were photographed as far south as Mexico, Japan, and southern Europe, regions located at latitudes between 25 and 40 degrees, where auroras are extremely rare.
The compression of Earth's magnetic field during the storm's most intense phase allowed charged particles to travel much farther along field lines toward the equator.
As the solar wind compressed the magnetosphere, the auroral oval expanded dramatically southward on the nightside of Earth and northward in the southern hemisphere.
Observers in central Japan witnessed vivid red auroras, caused by oxygen atoms at higher altitudes emitting light at a 630-nanometer wavelength, while green auroras from lower altitude oxygen emissions appeared across northern Europe.
These low-latitude auroras served as visible evidence of how severely the geomagnetic storm had disrupted Earth's normal magnetic field configuration and plasma environment.
How Will This Discovery Improve Space Weather Forecasting
The connection between negative ionospheric storms and delayed plasmasphere recovery had never been clearly observed and documented before this event, making the Arase data invaluable for improving space weather prediction models.
During the four-day recovery period, several satellites experienced electrical anomalies or temporarily stopped transmitting data, GPS positioning errors reached up to 70 meters in some regions, and high-frequency radio communications were disrupted.
Understanding the chemical processes that slow plasmasphere refilling helps forecasters predict how long these disruptions might persist after future superstorms.
Space weather forecasting relies on models that simulate how Earth's magnetosphere, plasmasphere, and ionosphere respond to solar activity.
By incorporating the observed relationship between atmospheric heating, chemical composition changes, and plasmasphere recovery rates, scientists can provide more accurate warnings about the duration of GPS degradation, satellite vulnerabilities, and communication blackouts.
With global infrastructure increasingly dependent on space-based systems, and with solar activity approaching the maximum phase of its 11-year cycle, these improved predictions will help operators take protective measures before, during, and after severe geomagnetic storms.
The May 2024 Mother's Day superstorm served as a natural laboratory for studying extreme space weather conditions that occur only once or twice per solar cycle.
As the Sun continues its approach toward solar maximum expected in late 2025, scientists anticipate additional opportunities to test and refine their understanding of how Earth's plasma environment responds to powerful solar eruptions.
The Arase satellite remains operational and positioned to capture future events, building a comprehensive dataset that will strengthen our ability to forecast, mitigate, and adapt to the challenges posed by an active Sun.
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