Magnetic Field Geometry and Anisotropic Scattering Effects on Solar Radio Burst Observations

TL;DR

This paper investigates how anisotropic turbulence and magnetic field geometry in the solar corona influence the observed properties of solar radio bursts, explaining source motions, bifurcations, and temporal broadening effects.

Contribution

It introduces a novel simulation approach incorporating anisotropic scattering and magnetic field structures to explain complex radio burst observations.

Findings

Sources move along magnetic field lines, not density gradients.

Anisotropic scattering causes source bifurcation into two components.

Scattering reduces the apparent frequency drift rate of fine structures.

Abstract

The fine structures of solar radio bursts reveal complex dynamics in the corona, yet the observed characteristics of these sub-second bursts are additionally complicated by radio wave scattering in the turbulent solar corona. We examine the impact of anisotropic turbulence in radio-wave propagation simulations with non-radial magnetic field structures in shaping the morphology, time-characteristics, and source position of fine structures. The apparent sources are found to move along the direction of the magnetic-field lines and not along the density gradient, whereas the major axis of the scattered source is perpendicular to the local magnetic field (the scattering anisotropy axis). Using a dipolar magnetic field structure of an active region, we reproduce observed radio fine structure source motion parallel to the solar limb associated with a coronal loop and provide a natural explanation for puzzling observations of solar radio burst position motions with LOFAR. Furthermore, the anisotropy aligned with a dipolar magnetic field causes the apparent source images to bifurcate into two distinct components, with characteristic sizes smaller than in unmagnetized media. The temporal broadening induced by scattering reduces the observed frequency drift rate of fine structures, depending on the contribution of scattering to the time profile. The findings underscore the role of magnetic field geometry and anisotropic scattering for the interpretation of solar radio bursts and highlight that anisotropic scattering produces more than a single source.