Tracing the Heliospheric Magnetic Field via Anisotropic Radio-Wave Scattering

Sep 15, 2026

Astrophysical radio sources are embedded in turbulent magnetised environments. In the 1 MHz sky, solar radio bursts are the brightest sources, produced by electrons travelling along magnetic field lines from the Sun through the heliosphere. Using multi-vantage-point type III observations and anisotropic radio-wave propagation simulations, the interplanetary field structure is shown to be encoded in radio emission directivity, enabling disentanglement of anisotropic scattering from electron motion and unveiling emission source locations, consistent with the Parker field.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages14

Reading Time35 min

AccessFree to download

Abstract

Introduction

arXiv :2503 .22553v1 [ astro-ph . SR] 28 Mar 2025 Tracing the Heliospheric Magnetic Field via Anisotropic Radio-Wave Scattering Daniel L. Clarkson 1,* , Eduard P. Kontar 1 , Nicolina Chrysaphi2,1 , A. Gordon Emslie3 , Natasha L. S. Jeffrey4 , Vratislav Krupar5,6 , and Antonio Vecchio7,8 1 School of Physics and Astronomy, University of Glasgow, G12 8QQ, United Kingdom 2 Sorbonne Universit , ´Ecole Polytechnique, Institut Polytechnique de Paris, CNRS, Laboratoire de Physique des Plasmas (LPP), 4 Place Jussieu, 75005 Paris, France 3 Department of Physics & Astronomy, Western Kentucky University, Bowling Green, KY 42101, USA 4 Department of Mathematics, Physics & Electrical Engineering, Northumbria University, Newcastle upon Tyne, NE1 8ST, United Kingdom 5 Goddard Planetary Heliophysics Institute, University of Maryland, Baltimore County, Baltimore, MD 21250, USA 6 Heliospheric Physics Laboratory, Heliophysics Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 7 Radboud Radio Lab-Department of Astrophysics, Radboud University, Nijmegen, The Netherlands 8 LESIA, Observatoire de Paris, Universit PSL, CNRS, Sorbonne Universit, Universit de Paris, 5 place Jules Janssen, 92195 Meudon, France * [daniel.clarkson@glasgow.ac.uk](daniel.clarkson@glasgow.ac.uk) ABSTRACT Astrophysical radio sources are embedded in turbulent magnetised environments. In the 1 MHz sky, solar radio bursts are the brightest sources, produced by electrons travelling along magnetic field lines from the Sun through the heliosphere. We demonstrate that the magnetic field not only guides the emitting electrons, but also directs radio waves via anisotropic scattering from density irregularities in the magnetised plasma. Using multi-vantage-point type III solar radio burst observations and anisotropic radio wave propagation simulations, we show that the interplanetary field structure is encoded in the observed radio emission directivity, and that large-scale turbulent channelling of radio waves is present over large distances, even for relatively weak anisotropy in the embedded density fluctuations. Tracing the radio emission at many frequencies (distances), the effects of anisotropic scattering can be disentangled from the electron motion along the interplanetary magnetic field, and the emission source locations are unveiled. Our analysis suggests that magnetic field structures within turbulent media could be reconstructed using radio observations and is found consistent with the Parker field, offering a novel method for remotely diagnosing the large-scale field structure in the heliosphere and other astrophysical plasmas. Introduction The majority of astrophysical radio sources are found in turbulent and magnetised environments (e.g., the intergalactic medium, pulsar nebulae, stellar coronae, and planetary magnetospheres) . As the emitted radio waves propagate through such background media, they can scatter both elastically and inelastically from ambient density inhomogeneities, resulting in a variety of effects such as shifts in apparent position and angular broadening. Radio wave propagation effects offer not only unique diagnostics (e.g., using plasma dispersion and scattering of fast radio bursts to determine distances 1 ) but also enormous challenges (e.g., effecting a seeing limitation2 ) . Despite decades of observations, the details of particle transport from the Sun through the heliosphere remains a largely open question in space physics3. During solar (and stellar) flares, energetic electrons are ubiquitously accelerated4–6, and some of these electrons escape into interplanetary space7–10 along the guiding magnetic field lines of the Parker spiral 11. These electrons are responsible for the generation of so-called type III solar radio bursts, in which electromagnetic radiation at radio frequencies is generated via plasma emission processes near the local plasma frequency fpe (MHz) ≃ 8.9 × 10−3n1p/2 and/or its

FAQs

How do type III solar radio bursts relate to the heliospheric magnetic field?

Type III bursts are produced by electrons traveling along guiding magnetic field lines in the heliosphere, and the radio-wave emission directionality reflects the interplanetary field structure.

What role does anisotropic radio-wave scattering play in the observations?

Anisotropic scattering from density irregularities directs radio waves preferentially along the magnetic-field direction, so apparent source locations from triangulation differ from intrinsic emission locations.

How can scattering effects be separated from electron motion?

By tracing radio emission at many frequencies (and thus different distances), the analysis disentangles anisotropic scattering signatures from electron transport along the interplanetary magnetic field.

Sep 15, 2026

Uploaded by Quinn Holloway