The Effect of the Parametric Decay Instability on the Morphology of Coronal Type III Radio Bursts

The nonlinear evolution of Alfv\'en waves in the solar corona leads to the generation of Alfv\'enic turbulence. This description of the Alfv\'en waves involves parametric instabilities where the parent wave decays into slow mode waves giving rise to density fluctuations. These density fluctuations, in turn, play a crucial role in the modulation of the dynamic spectrum of type III radio bursts, which are observed at the fundamental of local plasma frequency and are sensitive to the local density. During observations of such radio bursts, fine structures are detected across different temporal ranges. In this study, we examine density fluctuations generated through the parametric decay instability (PDI) of Alfv\'en waves as a mechanism to generate striations in the dynamic spectrum of type III radio bursts using magnetohydrodynamic simulations of the solar corona. An Alfv\'en wave is injected into the quiet solar wind by perturbing the transverse magnetic field and velocity components which subsequently undergo the PDI instability. The type III burst is modelled as a fast-moving radiation source that samples the background solar wind as it propagates to emit radio waves. We find the simulated dynamic spectrum to contain striations directly affected by the multi-scale density fluctuations in the wind.
Comment: Accepted for publication in The Astrophysical Journal Letters, PSP focus issue