Detecting the oscillation and propagation of the nascent dynamic solar wind structure at 2.6 solar radii using VLBI radio telescopes

TL;DR

This study uses VLBI radio telescopes to observe and analyze the oscillation and propagation of the early-stage solar wind at 2.6 solar radii during a CME event, revealing wave phenomena and velocity variations.

Contribution

It demonstrates high-resolution detection of solar wind oscillations and propagation using ground-based VLBI, providing new insights into solar wind dynamics during CME passage.

Findings

Detection of streamer wave via tangential velocity oscillation

Observation of accelerating fast density structures indicating MHD waves

Validation of ground station-pairs for high-resolution solar wind studies

Abstract

Probing the solar corona is crucial to study the coronal heating and solar wind acceleration. However, the transient and inhomogeneous solar wind flows carry large-amplitude inherent Alfven waves and turbulence, which make detection more difficult. We report the oscillation and propagation of the solar wind at 2.6 solar radii (Rs) by observation of China Tianwen and ESA Mars Express with radio telescopes. The observations were carried out on Oct.9 2021, when one coronal mass ejection (CME) passed across the ray paths of the telescope beams. We obtain the frequency fluctuations (FF) of the spacecraft signals from each individual telescope. Firstly, we visually identify the drift of the frequency spikes at a high spatial resolution of thousands of kilometers along the projected baselines. They are used as traces to estimate the solar wind velocity. Then we perform the cross-correlation analysis on the time series of FF from different telescopes. The velocity variations of solar wind structure along radial and tangential directions during the CME passage are obtained. The oscillation of tangential velocity confirms the detection of streamer wave. Moreover, at the tail of the CME, we detect the propagation of an accelerating fast field-aligned density structure indicating the presence of magnetohydrodynamic waves. This study confirm that the ground station-pairs are able to form particular spatial projection baselines with high resolution and sensitivity to study the detailed propagation of the nascent dynamic solar wind structure.