Speaker
Description
Sub-second fine structures of solar radio bursts reveal complex dynamics in the corona, yet their observed features are additionally complicated by radio-wave scattering in the turbulent corona. LOFAR imaging of individual fine structures during a single event revealed puzzling, non-radial motions of apparent sources at superluminal speeds and rapid expansion on millisecond timescales. We examine how anisotropic turbulence and non-radial magnetic field structures shape the morphology, timing, and source positions of these fine structures using radio-wave propagation simulations. We find that apparent source motion follows magnetic field lines rather than the density gradient, and that the major axis of the scattered source is perpendicular to the local field. Using a dipolar magnetic field model of an active region, we reproduce the observed source motion parallel to the solar limb, providing a natural explanation for the LOFAR observations. The observed fine structure drift-rate is also influenced by the source location within the field structure, due to variations in temporal broadening. Strong 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 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.
