New Delhi: Astronomers have investigated a Coronal Mass Ejection that travelled from the Sun to Earth in March 2023, revealing how even subtle solar eruptions can trigger intense geomagnetic storms and complicate space weather forecasting.
The study found that the CME propagated through a coronal hole – an opening in the Sun’s magnetic field lines – allowing solar wind streams to escape and significantly influence Earth’s near-space environment.
Understanding Coronal Mass Ejection and Its Impact on Space Weather
A Coronal Mass Ejection (CME) refers to a powerful expulsion of plasma and magnetic fields from the Sun’s atmosphere. Such events can cause geomagnetic storms that disrupt satellites, communication networks, navigation systems, and power grids on Earth.
However, scientists note that nearly 10% of intense geomagnetic storms are not linked to obvious large-scale solar eruptions, but instead originate from weak or stealth CMEs that often go undetected due to current observational limitations.
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Stealth Coronal Mass Ejection Behind March 2023 Geomagnetic Storm
In the recent study, astronomers examined a stealth Coronal Mass Ejection that occurred on 19 March 2023 and led to an intense geomagnetic storm on Earth approximately three days later.
Using multi-spacecraft observations from NASA missions, researchers identified that even weak CMEs with southward magnetic field components and enhanced plasma density can have significant effects on Earth’s space environment.
The CME originated from the eruption of a longitudinal filament channel near the centre of the Sun. Unlike conventional strong CMEs, this event was not accompanied by X-ray flares or radio bursts, making it exceptionally difficult to detect with standard solar monitoring techniques.
Role of Coronal Holes in CME Propagation
The stealth CME was investigated by researchers at the Indian Institute of Astrophysics (IIA), an autonomous institution under the Department of Science and Technology (DST), Government of India.
According to lead author P Vemareddy, such weak CMEs leave minimal detectable signatures on the Sun, posing major challenges for space weather prediction.
The team analysed data from multiple spacecraft, including NASA’s Solar Dynamics Observatory (SDO), Solar Orbiter (SolO), STEREO-A, and WIND.
Extreme Ultraviolet images from SDO revealed the presence of a coronal hole near the CME’s source region. When CMEs erupt close to coronal holes, they can be carried by high-speed solar wind streams.
Researchers found that the nearby coronal hole likely enabled the CME to travel efficiently from the Sun to Earth, rather than dissipating close to the solar surface.
Tracking the Interplanetary Coronal Mass Ejection
The study examined the radial evolution of the interplanetary Coronal Mass Ejection (ICME) using in situ observations from SolO, STEREO-A, and WIND, which were nearly aligned radially from the Sun.
The ICME travelled behind a high-speed solar wind stream and was detected without a distinct shock or sheath structure.
Observations showed that the associated magnetic cloud expanded as it propagated, with decreasing velocity, increasing radial size – from 0.08 AU at SolO to 0.18 AU at STEREO-A – and reduced expansion speed.
The magnetic field exhibited rotation during its journey, with right-handed helicity consistent with the CME’s solar source region.
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Geomagnetic Storm Modelling Confirms CME Impact
Enhanced plasma density was observed near the boundaries of the magnetic cloud within the ICME. Researchers modelled the geomagnetic storm intensity using parameters such as solar wind velocity, plasma density, magnetic field orientation, and electric fields.
The modelled results closely matched observed geomagnetic indices, particularly when variations in solar wind density and electric fields were included.
The findings demonstrate that a subtle Coronal Mass Ejection, despite being inconspicuous near the Sun, can evolve dynamically through the heliosphere and drive intense geomagnetic storms on Earth.
This evolving behaviour underscores the growing challenges in forecasting space weather impacts arising from stealth CMEs.
The study was published in The Astrophysical Journal under the title “An Intense Geomagnetic Storm Originated from Stealth Coronal Mass Ejection: Remote and In Situ Observations by Near Radially Aligned Spacecraft”.
The paper was authored by P Vemareddy of IIA and K Selva Bharathi of IISER Tirupati, an MSc internship student at IIA.
