Rare solar radiation storm hits Earth: S4 level details

In an exceptional astronomical event, unprecedented in scientific records for many years, scientists from the Solar Astronomy Laboratory at the Space Research Institute of the Russian Academy of Sciences observed solar radiation storm classified as level S4. This storm has begun directly impacting the space environment surrounding Earth, registering a level of disturbance not seen for more than two solar cycles.

Storm details and measurement levels

The research team explained that monitoring instruments recorded a sudden and sharp jump in the solar proton flux, exceeding 10,000 flux units. Scientists confirmed that the storm reaching level S4 is unprecedented in nearly two decades. It is scientifically known that the solar radiation storm scale theoretically ends at level S5, a limit that has never been actually recorded in the history of modern astronomical observations. The historical record remains at approximately 40,000 flux units, recorded in the last century.

X-class solar flare

These violent cosmic disturbances follow a massive solar flare that occurred last Sunday, classified as an X-class flare, the most powerful and influential category in the solar flare classification. This flare, the first of its kind since early 2026, unleashed a torrent of charged particles toward Earth, registering the highest flow rate in the last ten years. Laboratory experts indicated that this event raises profound scientific questions, especially since overall solar activity appeared to be below levels that could explain such a powerful burst of radiation.

Expected impacts of S4 category storms

Scientifically, radiation storms of level S4 are classified as "severe" and have significant impacts on space technology and activities. According to international space weather monitoring standards, this level of radiation can cause problems with satellite memory systems and disrupt star trackers used by spacecraft for navigation, potentially leading to temporary loss of control. These storms also pose a radiation hazard to astronauts in space and often disrupt high-frequency (HF) radio communications in polar regions, affecting air and sea traffic in those areas.

Solar cycle 25 and unprecedented activity

Scientists have described the confluence of physical conditions that directed this burst of radiation toward Earth as an "extremely rare coincidence." This event occurred within the context of Solar Cycle 25, which officially began in December 2019. Solar cycles are a natural process that recurs approximately every 11 years, during which the Sun's magnetic poles reverse their positions. The current cycle has proven to be more active and turbulent than predicted by space-based weather models, registering an unexpected peak in intensity. This underscores the critical importance of developing space weather early warning systems to protect Earth's technological infrastructure.