Aditya-L1 data show a 2024 solar eruption expanded unevenly, not as a symmetric bubble

Indian scientists using the Visible Emission Line Coronagraph (VELC) on the Aditya-L1 solar mission have found that a coronal mass ejection (CME) seen on 5 August 2024 did not expand as a symmetric bubble. The paper, by Saurabh Tripathi, Tanmoy Samanta and Jayant Joshi, is published in The Astrophysical Journal Letters (volume 1009, L24), according to its arXiv record. GKToday dates the publication to 3 November 2026; we read the paper's abstract on arXiv, not the full text.

What the paper reports

The team studied the eruption using VELC's spectra of the Fe XIV 5303 Å coronal line together with images from the Atmospheric Imaging Assembly on NASA's Solar Dynamics Observatory. VELC caught the erupting CME as it crossed its western slit. The abstract says the spectra show coronal dimming and enhanced Doppler velocities during the eruption, and "strongly Doppler-shifted secondary components" tied to the CME front. These appear as two separate emission branches on opposite sides of the line's rest wavelength, a split spectral shape that the authors call bifurcated.

The key measurements, as given in the abstract:

• line-of-sight plasma velocities of up to 218 km/s, "likely a lower limit" because the secondary component reaches the edge of the spectral window;
• a projected radial speed of 1,135 km/s from the imaging data; and
• a sideways speed in the plane of the sky of 692 km/s along the slit, which is lower than the radial speed.

How they interpreted it

To explain the pattern the authors built a simplified three-dimensional model of an expanding, tilted CME shell. Their synthetic spectra show that an inclined CME expanding unevenly sideways can produce a split spectral shape like the one observed, with velocity components along the radial, sideways and line-of-sight directions. They conclude that combining spectroscopy with ultraviolet imaging constrains different parts of a CME's motion during its early stage.

Why it matters

CMEs are clouds of plasma thrown from the Sun that can disturb satellites and power systems if they reach Earth. How a CME grows in the lower corona helps determine its speed and direction, so forecasting models that assume a symmetric bubble may misjudge it. The paper is a single-event study, based on one eruption, and it describes a simplified model; it does not itself present a new forecasting method.

Background

The earlier Aditya-L1 results this season include a separate VELC study of CME-linked broadening of the same coronal line, available on arXiv, and, GKToday reported, a joint analysis with Europe's Proba-3 mission published on 15 October. Aditya-L1 operates around the Sun-Earth L1 region.

Coverage of the paper is thin, so the abstract is the main record of its claims. The authors' model is deliberately simplified: it treats the CME as an expanding, tilted shell, and the match with the observed spectra shows the pattern is possible, not that the model is the only explanation.

What to watch

The authors note that the line-of-sight velocity may be underestimated. Further events observed by VELC, and comparison with other coronagraphs, would show whether uneven expansion is common.