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

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.

16 pages, 12 figures. Accepted in The Astrophysical Journal

References in corpus (10)

• Dynamics of electron beams in the inhomogeneous solar corona plasma
• Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer
• An Anisotropic Density Turbulence Model from the Sun to 1 au Derived From Radio Observations
• Sub-second time evolution of Type III solar radio burst sources at fundamental and harmonic frequencies
• Radio Echo in the Turbulent Corona and Simulations of Solar Drift-Pair Radio Bursts
• Solar Fast Drifting Radio Bursts in an X1.3 Flare on 2014 April 25
• LOFAR observations of radio burst source sizes and scattering in the solar corona
• First Frequency-Time-Resolved Imaging Spectroscopy Observations of Solar Radio Spikes
• Solar Radio Spikes and Type IIIb Striae Manifestations of Sub-second Electron Acceleration Triggered by a Coronal Mass Ejection
• The frequency ratio and time delay of solar radio emissions with fundamental and harmonic components