Coronal flux tube illuminated by strong shock spot: New Year's Eve solar eruption of 2023-Dec-31
Illya Plotnikov, Alexis P. Rouillard, Athanasios Kouloumvakos, Immanuel Jebaraj
TL;DR
This study addresses how coronal shock surfaces in solar eruptions produce radio emissions and energetic particles by linking EUV/white-light observations with a 3D MHD coronal model to synthesize a shock-driven radio spectrum. The authors apply a 2023-12-31 X5 flare/CME event, reconstruct the evolving shock, and map local Alfvén Mach numbers to the emission via the local plasma frequency, identifying a transient high-$M_A$, quasi-perpendicular hotspot near a pseudo-streamer cusp that explains both the EUV precursor and a reverse-drift radio feature. They further show that later interactions between the shock and the heliospheric current sheet reproduce the low-frequency type-II bursts, reinforcing the role of high-$M_A$ regions in particle acceleration. The work demonstrates a robust framework to connect coronal-shock physics with radio signatures and energetic-particle phenomenology, with potential generalization to other events.
Abstract
Powerful solar eruptions are known to produce fast and wide shock waves in the solar corona and inner heliosphere. The relationship between the coronal shock waves, solar energetic particles and different types of radio emission is a subject of long-lasting research activity. In this work, we perform a case study of 31 December 2023 eruption that occurred near eastern limb of the Sun. It produced a X5.0 class X-ray flare, a global EUV wave, a fast $\sim3000$ km/s Coronal Mass Ejection, strong radio emissions (including several type III and type II bursts), solar energetic particles in-situ, and long duration high-energy gamma-ray emission. We employ a technique that combines the reconstructed coronal shock from observations with background coronal MHD simulations to produce shock-mediated synthetic radio spectrum, assuming local emission at plasma frequency. We show that transient high Mach number and quasi-perpendicular coronal shock region explains both a ``hot flux tube'' precursor seen in EUV observations and reverse drifting radio spectral features observed by ground-based facilities. The occurrence of this evanescent strong shock patch was observed when it propagated across pseudo-streamer's cusp where the magnetic field was particularly low. We also find evidence that, at higher coronal altitudes, the low-frequency type II radio burst detected by several spacecraft, is triggered by the interaction of the shock with the heliospheric current sheet. This study provides additional evidence that high-$M_A$ regions of coronal shock surface are instrumental in energetic particle phenomenology.