Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Maoli Ma
Guifré Molera Calvés
Giuseppe Cimò
Peijin Zhang
Xiong Ming
Peijia Li
Pradyumna Kummamuru
zhanghu Chu
Tianyu Jiang
Bo Xia
Kondo Tetsuro
Fengxian Tong
Pablo de Vicente
Jonathan Quick
Hua Zhang
Zhong Chen
Abstract： The ESA's Mars Express solar corona experiments were performed at two solar conjunctions in the years 2015 and 2017 by a number of radio telescopes in the European VLBI Network. This paper presents the methods to measure the frequency and phase fluctuations of the spacecraft radio signal, and the applications to study the characteristics of the plasma turbulence effects on the signal at a single station and at multiple stations via cross-correlation. The power spectra of the frequency fluctuations observed between 4.9 and 76.3 $\rm R_{s}$ have a power-law shape close to a Kolmogorov spectrum over the frequency interval $ \nu_{lo}< \nu <\nu_{up}$, where the nominal value of $\nu_{lo}$ is set to 3 mHz and $\nu_{up}$ is in the range of 0.03 $\sim$ 0.15 Hz. The RMS of the frequency fluctuations is presented as a function of the heliocentric distance. Furthermore, we analyse the variations of the electron column density fluctuations at solar offsets 4.9 $\rm{R_{s}}$ and 9.9 $\rm{R_{s}}$ and the cross-correlation products between the VLBI stations. The power density of the differential fluctuations between different stations decreases at $\nu < 0.01$ Hz. Finally, the fast flow speeds of solar wind $>700$ $\rm{km~s^{-1}}$ are derived from the cross-correlation of frequency fluctuations at $\nu < 0.01$ Hz. The fast flow speeds of solar wind correspond to the high heliolatitude of the coronal region that the radio rays passed. The VLBI observations and analysis methods can be used to study the electron column density fluctuations and the turbulence at multiple spatial points in the inner solar wind by providing multiple lines of sight between the Earth and the spacecraft.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Maoli Ma
Guifre Molera Calves
Giuseppe Cimo
Ming Xiong
Peijia Li
Jing Kong
Peijin Zhang
Jiansen He
Lijia Liu
Pradyumna Kummamuru
Chuanpeng Hou
Jasper Edwards
Qinghui Liu
Zhong Chen
Zhanghu Chu
De Wu
Xu Zhao
Zhichao Wang
Songtao Han Quanquan Zhi
Yingkai Liu
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.
Peer Review Status:Awaiting Review
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