How the 2024 solar superstorm drained Earth's radiation belt

In May 2024, Earth encountered its most potent geomagnetic storm since the Halloween storms of 2003. This superstorm left night skies illuminated with vibrant auroras and caused disruptions to certain infrastructure, such as GPS signals utilized by farming machinery. Satellite observations disclosed a significant loss of high-energy electrons from Earth's outer Van Allen radiation belt during the storm.

Researchers Xingzhi Lyu and colleagues have now conducted an exhaustive examination of the mechanism behind this rapid electron transport, with vital ramifications for future space weather predictions. Their findings are published in the journal AGU Advances.

The Van Allen radiation belts are donut-shaped bands that encircle our planet, containing energetic electrons and protons—predominantly originating from the solar wind—trapped by Earth's magnetosphere. Geomagnetic storms can alter the magnetosphere, triggering abrupt shifts in electron behavior within the outer radiation belt, which may pose threats to satellites.

Despite extensive research on these hazards, the mechanisms of rapid electron transport in the radiation belts during exceptionally intense storms have remained elusive. The May 2024 superstorm offered a unique opportunity to study this phenomenon. The scientists analyzed data from the Japan Aerospace Exploration Agency's Arase satellite, determining the drastic reduction of electrons within the outer radiation belt during the superstorm.

To investigate the underlying physical processes responsible for the swift electron loss, they employed the Versatile Electron Radiation Belt (VERB) model, which is specifically designed to mimic radiation belt dynamics. They discovered that two previously documented processes were the main culprits of electron loss: magnetopause shadowing, which transported electrons outward and expelled them into space, and local wave scattering, which moved electrons inward into Earth's upper atmosphere.

The relative contribution of each process varied across different areas of Earth's magnetic field. Crucially, for the simulations to precisely replicate the real-world extreme electron loss, the commencement of sudden, outward electron transport linked with magnetopause shadowing had to transpire almost simultaneously with a substantial compression of Earth's magnetosphere that occurred during the superstorm.

This compression was then followed by local wave scattering. Conventional models of electron transport frequently utilized in space weather forecasting fail to accurately encapsulate the tightly coupled timing of superstorm dynamics and electron transport processes unveiled in this study. The new insights could aid in refining models, potentially leading to more accurate superstorm forecasting and risk assessment.