Aditya-L1 Uncovers Asymmetric Expansion of Solar Eruption, Offering New Insights into Space Weather Forecasting

Scientists from the Indian Institute of Astrophysics (IIA), an autonomous institution under the Department of Science and Technology (DST), have reconstructed the three-dimensional structure and dynamics of a solar eruption by combining observations from Aditya-L1’s Visible Emission Line Coronagraph (VELC), NASA’s Solar Dynamics Observatory (SDO) and advanced three-dimensional modelling.

The findings, published in The Astrophysical Journal Letters, demonstrate how the expansion characteristics of CMEs can differ in different directions. Such variations may influence the speed and trajectory of solar eruptions as they travel through interplanetary space towards Earth, potentially affecting the intensity and timing of space-weather disturbances.

Aditya-L1 Provides New Insights into Solar Eruptions

Launched in September 2023, Aditya-L1 is India’s first dedicated space-based solar observatory. Positioned at the Sun–Earth Lagrange Point 1 (L1), the spacecraft provides continuous observations of the Sun and its surrounding atmosphere.

The mission carries seven scientific payloads designed to study different aspects of solar activity. Among them, the Visible Emission Line Coronagraph (VELC) is the primary payload and is designed to observe the solar corona using multiple observational modes.

VELC is an internally occulted coronagraph capable of studying the Sun’s outer atmosphere and capturing the early stages of solar eruptions. Its unique spectroscopic capabilities allow scientists to investigate the movement of hot plasma in the corona, providing information that cannot be obtained from conventional imaging alone.

Study of August 5, 2024, Solar Eruption

The research team examined a Coronal Mass Ejection that occurred on August 5, 2024. The eruption originated from an active region near the western limb of the Sun.

The scientists analysed observations from VELC alongside data collected by the Atmospheric Imaging Assembly (AIA) onboard NASA’s Solar Dynamics Observatory.

Saurabh Tripathi, a PhD student at the Indian Institute of Astrophysics and lead author of the study, explained that the team observed the CME using both Aditya-L1 and NASA’s SDO spacecraft.

The observations revealed an unusual Doppler pattern in the emission detected by VELC, with both blueward-shifted and redward-shifted signals. These shifts indicate plasma moving towards and away from the observer, respectively.

This provided important information about the movement of the expanding solar material along the line of sight.

VELC Detects Uneven Expansion of Coronal Mass Ejection

The observations revealed that the CME did not expand uniformly in all directions. Instead, it developed an asymmetric structure as it moved away from the Sun.

While the AIA instrument onboard NASA’s SDO captured the CME’s movement across the plane of the sky, VELC provided crucial information about the plasma’s motion towards and away from the observer.

Combining these complementary observations enabled researchers to obtain a more comprehensive understanding of the eruption’s three-dimensional movement.

Tanmoy Samanta, a solar astronomer at IIA and corresponding author of the study, explained that the combined observations showed that the CME was not expanding like a simple spherical bubble. Its uneven expansion resulted in an asymmetric shape.

This finding challenges the simplified assumption that solar eruptions expand uniformly in all directions and highlights the importance of studying their three-dimensional structure.

Three-Dimensional Modelling Explains the Unusual Pattern

To understand the unusual spectral signatures detected by VELC, the research team developed a three-dimensional geometric-kinematic model of the expanding CME.

Jayant Joshi of IIA, a co-author of the study, explained that the model was used to investigate how the orientation of the CME and its uneven sideways expansion could produce the observed spectral patterns.

The researchers found that a model assuming symmetrical expansion could not reproduce the Doppler signatures recorded by VELC.

However, a model incorporating an inclined CME axis and asymmetric lateral expansion produced spectral patterns and changes over time that closely matched the actual observations.

This modelling approach helped the scientists reconstruct the three-dimensional geometry and dynamics of the solar eruption using observations from different instruments.

How VELC Studies the Solar Corona

VELC studies the early stages of CMEs through spectroscopy in the 530.3-nanometre green emission line. This emission originates from highly ionised iron atoms present in the solar corona and traces hot coronal plasma at temperatures of approximately 1.8 million Kelvin.

One of VELC’s important capabilities is measuring the Doppler shift, which refers to changes in the wavelength of light caused by the movement of emitting material.

A blueward shift indicates plasma moving towards the observer, while a redward shift indicates movement away from the observer. By measuring these changes, scientists can estimate plasma velocities along the line of sight, particularly in regions close to the solar disk.

This capability makes VELC particularly valuable for studying the early development of solar eruptions, when their structures are evolving rapidly.

The instrument was designed and fabricated by the Indian Institute of Astrophysics at its M.G.K. Menon Laboratory for Space Sciences on the CREST campus in Hosakote, Karnataka, with substantial support from the Indian Space Research Organisation (ISRO).

Significance for Future Space Weather Research

Coronal Mass Ejections are large eruptions of magnetised plasma and magnetic fields from the Sun. When directed towards Earth, they can interact with Earth’s magnetic field and trigger geomagnetic disturbances.

These disturbances can affect satellite operations, radio communications, navigation systems, power infrastructure and other technological networks.

Understanding how CMEs expand and travel through space is therefore essential for improving space-weather monitoring and forecasting.

The latest study demonstrates that information about the three-dimensional motion of solar eruptions can be obtained by combining spectroscopic observations with imaging and modelling techniques.

The research team plans to apply this approach to other CMEs to reconstruct their movement without depending entirely on observations from multiple space-based viewpoints.

This technique could be particularly useful for studying the lower solar corona, where CMEs evolve rapidly and their movement along the line of sight cannot be determined through imaging alone.

The findings highlight the scientific importance of Aditya-L1’s VELC payload and demonstrate how India’s solar mission is contributing to a deeper understanding of solar activity. By improving knowledge of the structure, expansion and movement of solar eruptions, the mission could help advance future space-weather research and forecasting capabilities.