A recent scientific investigation has revealed how a subtle, hard-to-detect solar eruption can trigger an intense geomagnetic storm on Earth, underscoring new challenges in space weather prediction. Astronomers studied a Stealth Coronal Mass Ejection (CME) that erupted from the Sun on 19 March 2023 and reached Earth roughly three days later, despite showing no conventional warning signs such as X-ray flares or radio bursts.
The findings demonstrate that even weak solar events can have significant terrestrial impacts, complicating efforts to forecast disruptions to satellites, communication systems, navigation networks, and power grids.
Understanding Stealth Coronal Mass Ejections
Coronal Mass Ejections (CMEs) are massive expulsions of plasma and magnetic fields from the Sun that can cause geomagnetic storms upon interacting with Earth’s magnetosphere. While most intense storms are linked to large, visible solar eruptions, around 10% of severe geomagnetic storms originate from weak or “stealth” CMEs that evade routine detection due to current observational limits.
Understanding these stealth events is critical, as they can produce strong geomagnetic effects without any obvious solar surface activity.
The March 2023 Stealth CME Event
In the study, astronomers examined a stealth CME that emerged from a longitudinal filament channel near the Sun’s centre. Unlike typical CMEs, this event occurred without accompanying X-ray flares or radio emissions, making it exceptionally elusive.
Using multi-spacecraft observations from NASA’s Solar Dynamics Observatory (SDO), Solar Orbiter (SolO), STEREO-A, and WIND, researchers traced the CME’s journey from the Sun to Earth and confirmed its role in triggering an intense geomagnetic storm.
Role of Coronal Holes in CME Propagation
Extreme ultraviolet images from SDO revealed the presence of a coronal hole near the CME’s source region. Coronal holes are openings in the Sun’s magnetic field that allow high-speed solar wind to escape.
According to the researchers, the nearby coronal hole likely aided the propagation of the stealth CME, allowing it to travel efficiently through space instead of dissipating near the Sun. This interaction enabled the CME—with its southward magnetic field component and enhanced plasma density—to reach Earth and cause significant geomagnetic disturbances.
Indian Scientists Lead the Investigation
The study was conducted by astronomers at the Indian Institute of Astrophysics (IIA), an autonomous institution under the Department of Science and Technology, Government of India.
Lead author P. Vemareddy explained that such weak CMEs “leave no detectable signatures on the Sun and hence are extremely difficult to identify with current observational sensitivity,” highlighting the need for improved monitoring techniques.
Insights from Interplanetary Observations
The researchers also analysed the interplanetary CME (ICME) using in-situ measurements from spacecraft positioned nearly along the same radial line from the Sun. The ICME was detected without a clear shock or sheath, travelling behind a high-speed solar wind stream.
Observations showed:
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Expansion of the associated magnetic cloud, with radial size increasing from 0.08 AU at Solar Orbiter to 0.18 AU at STEREO-A
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Decreasing velocity and reduced expansion speed during propagation
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Rotation of the magnetic field with right-handed helicity, consistent with the CME’s solar source region
These characteristics explain how a weak solar eruption can still evolve into a geoeffective structure by the time it reaches Earth.
Implications for Space Weather Prediction
The study highlights a critical gap in current space weather forecasting: dangerous geomagnetic storms can be triggered by solar events that leave almost no visible trace at the Sun. The interaction between stealth CMEs and coronal holes adds further complexity to predicting their trajectories and impacts.
Conclusion
This research underscores the importance of multi-spacecraft observations and improved detection methods to identify stealth CMEs and mitigate their potential risks. As reliance on satellite-based technologies grows, understanding and forecasting such subtle solar phenomena will be essential for safeguarding modern infrastructure and advancing space weather preparedness.
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Source: PIB
