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Multi-spacecraft radio observations trace the heliospheric magnetic field

Solar flares accelerate energetic electrons that escape into interplanetary space, guided by the Parker spiral magnetic field, and are responsible for the generation of the interplanetary Type III solar radio bursts. With multiple spacecraft now in orbit around the sun, we are in a unique position of observing the propagation of radio emission through the heliosphere from multiple vantage points.

A recent study by Daniel L. Clarkson and others demonstrates that the magnetic field not only guides the emitting electrons, but also directs radio waves via anisotropic scattering from density irregularities in the magnetized plasma of the interplanetary space.

To study this effect across large distances in the heliosphere, researchers used observations of 20 Type III bursts between ~0.9–0.2 MHz from the Parker Solar Probe, Solar Orbiter, STEREO-A and WIND spacecraft that were distributed around the sun.

To reproduce the observations, the simulations have been made to follow radio-waves. The research is in the journal Scientific Reports.

The simulations show that the radio-waves are guided by the heliospheric magnetic field via anisotropic scattering.

Assuming that the magnetic field guides only the emitting electrons while the radiation is weakly scattered cannot explain the directivity pattern in multi-spacecraft observations without invoking a much steeper curvature of the Parker spiral, the paper concludes.

Therefore, the emitted radio waves are also guided along the interplanetary field due to anisotropic scattering, affecting the radiation received by observers that are spatially separated around the sun.

The eastward deviation of the type III radio burst intensity with decreasing frequency (increasing distance) allows for the magnetic field to be traced to distances greater than that of the emitter path, offering a powerful diagnostic tool for space weather studies and a potentially wide-ranging diagnostic of the magnetic field structure of different astrophysical environments in which radio sources are embedded.