Spectroscopic signatures of nonuniform lateral expansion of a coronal mass ejection in the low corona with ADITYA-L1/VELC

Abstract

Coronal mass ejections (CMEs) undergo rapid evolution in the low corona (<2R⊙), yet their three-dimensional kinematics remain poorly constrained. We present a spectroscopic and imaging analysis of a CME observed on 2024 August 5 using the Visible Emission Line Coronagraph (VELC) on board ADITYA-L1 and Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observator (SDO). The VELC Fe XIV 5303 Å spectra captured the erupting CME as it crossed the western slit. Space-time maps from single-Gaussian fits reveal coronal dimming and enhanced Doppler velocities during the eruption. Detailed spectral analysis reveals strongly Doppler-shifted secondary components associated with the CME front. These components appear as two spatially separated emission branches on opposite sides of the rest wavelength, producing a distinct bifurcated spectral morphology superposed on the nearly stationary reduced-intensity coronal emission. Double-Gaussian fitting yields line-of-sight (LOS) plasma velocities of up to 218 km s −1, likely a lower limit as the secondary component reaches the edge of spectral window. AIA 211 Å observations measure a projected radial speed of 1135 km s −1, larger than the plane-of-sky (POS) lateral speed of 692 km s −1 along the slit. To interpret the observed CME evolution and spectral structure, we developed a simplified three-dimensional geometric-kinematic model of an expanding axially tilted CME shell. Synthetic spectra from the model show that an inclined CME undergoing asymmetric lateral expansion can produce a bifurcated spectral morphology similar to that observed, with velocity components projected in the radial, POS-lateral, and LOS-lateral directions. Our results demonstrate that combining spectroscopy and EUV imaging constrains different components of CME kinematics during early evolution.