Quasi-harmonic faraday-rotation fluctuations of radio waves when sounding the outer solar corona

Faraday rotation fluctuations of MESSENGER radio signals through the equatorial lower corona near solar minimum

“…The FRF power spectrum (Figures and ) showed a power law form similar to that found in the HELIOS studies [ Efimov et al ., ; Bird , ; Efimov et al ., ]. We found it useful to separate the data analysis frame with the transient event from those showing only the general background fluctuation spectrum.…”

“…The 3.3 mHz peak corresponds to intermittent quasi‐harmonic oscillations of ~5 min period reported by Efimov et al . [] and Chashei et al . [] for FRF observations beyond 3 R ⊙ .…”

“…[] point out that the energy of Alfvén waves propagating in a turbulent medium can be transferred to other wave modes (i.e., magnetosonic) and may appear as a first harmonic peak in the power spectrum [see also Jensen , ]. Harmonic power spectral features are found in the earlier studies of HELIOS, e.g., 6–7 mHz enhancement [ Efimov et al ., , Figure 3] and 12–15 mHz [e.g., Bird , , Figure 12; Efimov et al ., , Figure 1]. The FR imprint of millihertz wave‐like activity in the lower corona is unequivocal, but further study is required to clarify FRF physical significance and relation to solar wind acceleration mechanisms.…”

“…[] and Efimov et al . [] described intermittent segments of quasi‐harmonic FRF along with power spectral wave‐scale organization generally consistent with the energy cascade concept. One particularly interesting feature was the presence of 5 min wave‐like oscillations in FR that appeared in up to 25% of the recordings obtained at heliocentric solar offsets above 3 R ⊙ .…”

The energy spectrum of spacecraft radio signals in the caustic shadow zone of the Sun: A new diagnostic of the solar coronal plasma

“…in solving an inverse problem, but also in solving a direct problem that implies predicting the propagation effects on spacecraft signals from knowledge of coronal plasma characteristics. When acted upon by large-scale inhomogeneities of the Sun's corona, radio waves undergo refraction, a regular frequency shift and Faraday rotation (Efimov et al, 2000;Efimov and Rudash, 2002). Statistical inhomogeneities of the corona modulate, in a random fashion, the frequency, phase and amplitude and can lead to a broadening of the energy spectrum of radio waves (Yakovlev et al, 1974;Efimov et al, 1978).…”