An Analysis of a Coronal Mass Ejection Leading Edge by Means of Multi-Spacecraft-in-Beam Phase Scintillation

TL;DR

The paper demonstrates that a multi-spacecraft-in-beam approach, using simultaneous MEX and TIW radio signals observed at a single VLBI antenna, can resolve the leading-edge structure of a CME via phase scintillation. By combining phase-residual analyses, cross-correlation across ray-paths, and echo-delay-based localization, the study links radio-propagation perturbations to CME density enhancements, turbulence regimes, and TEC changes, while corroborating with LASCO coronagraph imagery. The results show strong inter-spacecraft correlations during CME passage, reveal a shift in turbulence from pre-CME to CME conditions, and provide a first-order constraint on the CME’s location along the radio ray-path with velocity estimates around 755 ± 227 km s$^{-1}$. This technique offers complementary, line-of-sight-derived plasma diagnostics that can augment solar monitoring and space-weather forecasting, especially when integrated with future missions and coronagraphs.%

Abstract

A Coronal Mass Ejection (CME) was detected crossing the radio signals transmitted by the Mars Express (MEX) and Tianwen-1 (TIW) spacecraft at a solar elongation of $4.4^{o}$. The impact of the CME was clearly identifiable in the spacecraft signal SNR, Doppler noise and phase residuals observed at the University of Tasmania's Very Long Baseline Interferometry (VLBI) antenna in Ceduna, South Australia. The residual phases observed from the spacecraft were highly correlated with each other during the transit of the CME across the radio ray-path despite the spacecraft signals having substantially different Doppler trends. We analyse the auto- and cross-correlations between the spacecraft phase residuals, finding time-lags ranging between 3.18-14.43 seconds depending on whether the imprinted fluctuations were stronger on the uplink or the downlink radio ray-paths. We also examine the temporal evolution of the phase fluctuations to probe the finer structure of the CME and demonstrate that there was a clear difference in the turbulence regime of the CME leading edge and the background solar wind conditions several hours prior to the CME radio occultation. Finally, autocorrelation of the MEX two-way radio Doppler noise data from Ceduna and closed-loop Doppler data from ESA's New Norcia ground station antenna were used to constrain the location of the CME impact along the radio ray-path \add{to a region 0.2 AU from the Sun, at a heliospheric longitude consistent with CME origin at the Sun. The results presented demonstrate the potential of the multi-spacecraft-in-beam technique for studying CME structures in great detail, and providing measurements that complement the capabilities of future solar monitoring instruments.

Figures (11)

• Figure 1: Diagram of the multi-spacecraft-in-beam observing configuration. Note that the example spatial ordering of the spacecraft and radio antennas in the diagram is not necessarily reflective of ordering in the actual experiment.
• Figure 2: A compound image of the CME event on 3$^{rd}$ December 2023 at 06:54:07. The image overlay displays capture from SECCHI EUVI (171 Angstroms) (centre), LASCO C2 (inner) and C3 (outer) coronagraphs. The classic three-part CME structure is annotated.
• Figure 3: LASCO C2 and C3 CME leading edge height-time plot (measurements from the SOHO LASCO CME Catalogue).
• Figure 4: SNR (A), residual frequency (10-second sample rate) (B) and residual phase (C) from MEX (blue) and TIW (red) spacecraft observed at Ceduna on December $3^{rd}$ 2023.
• Figure 5: Example extracted phases and associated polynomial fits for MEX (A) and TIW (B), residual phase UserColor for MEX and TIW after removal of respective polynomial fits (C) and the difference between MEX and TIW phase residuals (D).