Local weather alerts are familiar warnings for potentially dangerous conditions, but an alert that puts all of Earth on warning is rare.

On May 31, the U.S. Naval Research Laboratory’s (NRL) space-based instrumentation captured real-time observations of a powerful coronal mass ejection (CME) that erupted from the sun, initiating a “severe geomagnetic storm” alert for Earth.

“Our observations demonstrated that the eruption was a so-called ‘halo CME,” meaning it was Earth-directed, with our preliminary analysis of the data showing an apparent velocity of over 1,700 kilometers per second for the event,” stated Karl Battams, Ph.D., computational scientist for NRL’s Heliospheric Science Division.

A geomagnetic storm is a major disturbance of Earth’s magnetosphere that’s caused by the highly efficient transfer of energy from the solar wind into our planet’s surrounding space environment. These disruptions are primarily driven by sustained periods of high-speed solar wind and, crucially, a southward-directed solar wind magnetic field that can peel away Earth’s field on the day side of the magnetosphere. Energy from the solar wind can open Earth’s magnetic shield.

The National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center classified the recent solar storm as G4, the second-highest classification on its five-level geomagnetic scale.

Powerful storms such as this are typically associated with CMEs. The repercussions can range from temporary outages and data corruption to permanent damage to satellites, increased atmospheric drag on low-Earth orbit spacecraft altering their trajectories, and disruptions to high-frequency radio communications.

“Such disturbances can compromise situational awareness, hinder command and control, affect precision-guided systems, and even impact the electrical power grid, directly affecting military readiness and operational effectiveness,” Battams said.

CMEs are colossal expulsions of plasma and magnetic field from the sun’s corona, often carrying billions of tons of material. While CMEs generally take several days to reach Earth, the most intense events have been observed to arrive in as little as 18 hours.

“CMEs are the explosive release of mass from the sun’s low corona and are a primary driver of space weather, playing a central role in understanding the conditions of Earth’s magnetosphere, ionosphere, and thermosphere,” explained Arnaud Thernisien, Ph.D., a research physicist from the Advanced Sensor Technology Section within NRL’s Space Science Division.

The May 30 event saw a relatively slow but powerful solar flare erupt from the Earth-facing side of the sun. The energy released blasted a CME directly toward Earth, leading to the geomagnetic storm that has produced auroras as far south as New Mexico.

NRL’s space-based instrumentation, operating on NASA and NOAA spacecraft, provided vital real-time observations of this event. Notably, NRL’s venerable Large Angle Spectrometric Coronagraph (LASCO), which has been in operation since 1996, and the Compact Coronagraph 1 (CCOR-1), launched in 2024, both relayed critical data.

Such observations are paramount for operational space weather monitoring, allowing forecasters to predict the timing of the event’s arrival at Earth and the potential geomagnetic storm it could induce. While precisely predicting the severity, exact timing, or duration of a geomagnetic storm remains challenging, these advance warnings are vital for enabling the Department of Defense (DoD) and other agencies to prepare.

The potential impacts of severe geomagnetic storms on DoD and Department of the Navy missions are significant and far-reaching. These events can disrupt or degrade critical systems and capabilities, including satellite communications, Global Positioning System (GPS) navigation and timing, and various remote sensing systems.

“NRL has been a pioneer in heliophysics and space weather research since the very inception of the field, dating back to the first discovery of CMEs through NRL space-based observations in 1971,” Battams said. “Since then, NRL has consistently maintained its position at the forefront of coronal imaging with a portfolio of groundbreaking instrumentation that has driven heliospheric and space weather studies.”

This includes:

• LASCO coronagraphs operating on the joint ESA-NASA Solar and Heliospheric Observatory (SOHO) mission since 1996
• Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument packages on the twin NASA Solar Terrestrial Relations Observatory (STEREO) spacecraft since 2006
• Wide-Field Imager for Parker Solar Probe (WISPR) instrument on NASA Parker Solar Probe (PSP) since 2018
• Solar Orbiter Heliospheric Imager (SoloHI) on ESA’s Solar Orbiter mission since 2019
• NOAA’s CCOR-1, designed and built by NRL, operating on NOAA’s GOES-19 since 2024

These assets, particularly instruments like LASCO and CCOR-1, are indispensable for providing the crucial real-time imagery necessary for forecasters to analyze and assess CMEs, determine Earth-impact likelihood, and issue timely warnings.

“They form the backbone of our ability to anticipate and mitigate the effects of space weather. As the G4 severe geomagnetic storm watch continues, the public and critical infrastructure operators are encouraged to visit NOAA’s Space Weather Prediction Center for the latest information and updates,” Thernisien said.

The journey of the CME, from its fierce eruption on the sun to its arrival at Earth, approximately one million miles away, highlights the dynamic nature of our solar system and the ongoing importance of NRL’s vital contributions to heliophysics research and space weather preparedness.

The data collected from events such as this will be instrumental in future research, further enhancing our understanding and predictive capabilities and ultimately bolstering the resilience of national security and critical infrastructure.