File(s) under permanent embargo
VLBI Data Processing on Coronal Radio-sounding Experiments of Mars Express
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 Rs have a power-law shape close to a Kolmogorov spectrum over the frequency interval νlo < ν < νup, where the nominal value of νlo is set to 3 mHz and νup is in the range of 0.03-0.15 Hz. The rms of the frequency fluctuations is presented as a function of the heliocentric distance. Furthermore, we analyze the variations of the electron column density fluctuations at solar offsets 4.9 Rs and 9.9 Rs and the cross-correlation products between the VLBI stations. The power density of the differential fluctuations between different stations decreases at ν < 0.01 Hz. Finally, the fast flow speeds of solar wind >700 km s-1 are derived from the cross correlation of frequency fluctuations at ν < 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.
History
Publication title
The Astronomical JournalVolume
162Issue
4Article number
141Number
141Pagination
1-13ISSN
0004-6256Department/School
School of Natural SciencesPublisher
Univ Chicago PressPlace of publication
1427 E 60Th St, Chicago, USA, Il, 60637-2954Rights statement
© 2021. The American Astronomical Society. All rights reserved.Repository Status
- Restricted