VLBI data processing on coronal radio-sounding experiments of Mars express

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 ${\mathrm{R}}_{\mathrm{s}}$ 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 ${\mathrm{R}}_{\mathrm{s}}$ and 9.9 ${\mathrm{R}}_{\mathrm{s}}$ 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 $>700$ $\mathrm{km}{\mathrm{s}}^{-1}$ 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.

References in corpus (4)

• Recent progress in astrophysical plasma turbulence from solar wind observations
• Reconstruction of Helio-latitudinal Structure of the Solar Wind Proton Speed and Density
• Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma
• Venus Express radio occultation observed by PRIDE

Cited by in corpus (3)

• Turbulence dynamics and flow speeds in the inner solar corona: Results from radio-sounding experiments by the Akatsuki spacecraft
• A monitoring campaign (2013-2020) of ESA's Mars Express to study interplanetary plasma scintillation
• Detecting the oscillation and propagation of the nascent dynamic solar wind structure at 2.6 solar radii using VLBI radio telescopes