The solar flares accelerate energy electrons that escape the interplanetary space, guided by the spiral magnetic field of Parker, and are responsible for the generation of interplanetary solar radio explosions type III. With multiple spacecraft now in orbit around the sun (see for example Musset et al 2021), we are in a unique position to observe the spread of radio broadcasting through the Helosphere from multiple points of view.
Recent study by Clarksson et al (https://www.nature.com/articles/s41598-025-95270-w) Show that the magnetic field not only guides the emitting electrons, but also directs the radio waves through the anisotropic dispersion of density irregularities in the magnetized plasma of the interplanetary space.
Figure 1. General description of a burst type III observed by four spacecraft. (a) Dynamic spectra. (b) Time profiles at four frequencies with escalated intensity at 1 au. (c) Panel intensity peaks (B) and directivity adjustment. (d) Lengths of the maximum tight intensity. The symbols show the positions of the spacecraft in the helosphere.
To study this effect through large distances in the helosphere, we use observations of 20 bursts type III between ~ 0.9-0.2 mhz of the Parker solar probe, the solar orbiter, the aesthetics and the wind spaceship that were distributed around the sun. Figure 1 shows an example event in which the same explosion is observed by the spacecraft separated by ~ 180 degrees, with the brightest intensity observed by the solar orbiter. The intensity distribution is considered by adjusting the maximum flows in each spacecraft (climbing to 1 au) for a given frequency with the equation (see eg Musset et al 2021),
\[I_{sc} = I_0\exp{\left(-\frac{1-\cos{(\theta_{sc}-\theta_0)}}{\Delta\mu}\right)},\]
where $ \ theta_0 $ gives the maximum adjusted intensity angle, and $ \ Delta \ mu $ describes the width of the directivity pattern (Figure 1c). In each event studied, we find a longitudinal change east of the maximum adjusted intensity and characterize the deviation for $ \ delta \ theta = \ theta_0 – \ theta_0 (0.9 \, \ mathrm {mhz}) $. Figure 2 shows that between 0.9-0.2 MHz, the peak has changed in -30 degrees on average. If the radiation propagates free of dispersion with any angular deviation only produced through the emitter movement along the Parker spiral, then said scenario would require a unrealistic solar wind rate of ~ 50 km s $^{-1} $, inconsistent with the measurements in situ.
Figure 2. Deviation in the length of the maximum intensity adjusted from 0.9 MHz. (A) It fits the observation data (gray). The red lines show the average and standard deviation. The blue and green bands show the deviation due to cases without dispersion. (b) Simulation data using different turbulence scale factors.
To reproduce the strong variation of 1 au flow with heliocentric length, we include a helium magnetic field model in the spiral -shaped of Parker to the simulation frame described by Kontar et al. 2023with an extension in the sun wind speeds between 340-420 km s $^{-1} $ and a scale of the turbulence amplitude $ (0.5-2) \ Times $. The resulting photons are dispersed in a wide range of heliocentric lengths, however, there is a different channeling along the field direction (Figure 3). We find that for typical heliospherical conditions, the results of the simulation reproduce the average deviation of ~ 30 degrees between 0.9-0.2 MHz (Figure 2b) with a propagation of ~ 10 degrees depending on the speed of the solar wind or the turbulence conditions.
Figure 3. Polar graphics of the propagation of simulated photons averaged in time in the helosphere to (a) a fundamental issuer (blue star) and (b) a harmonic issuer (green star). Colored histograms show the positions of the photons with the average wave vector in a given location shown by the black arrows. The box shows the approximate directivity at a distance where the dispersion rate is significantly lower.
Conclusion
Assuming that the magnetic field guides only the emitting electrons, while the radiation is weakly dispersed cannot explain the directivity pattern in the observations of several space spaces without invoking a much more pronounced curvature of the Parker’s spiral. We show that the radio broadcast waves They are also guided along the interplanetary field due to anisotropic dispersion, which affects the radiation received by observers who are spatially separated around the Sun. The deviation to the east of the intensity of Ráfaga of Radio Type III with a decreasing frequency (increasing distance) allows the magnetic field to be trace at distances greater than that of the emitter route, offering a powerful diagnostic tool for studies for studies Spatial meteorological and a potentially broad diagnosis of the structure of the magnetic field of the different astrophysical environments in which radio sources are wrapped.
Based on the recent article By Clarksson, DL, et al. Heliospheric magnetic field tracking through the dispersion of anisotropic radio radio, SCI REP 15, 11335 (2025). DOI: 10.1038/S41598-025-95270-W
References:
Clarksson, DL, et al., SCI REP 15, 11335 (2025)
MUSSET, S. et al., 2021, Astronomy and Astrophysics, 656, A34
Kontar, Ep, et al. 2023, APJ, 956, 112
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