Electromagnetic Simulations of Solar Radio Emissions

• Published in: Journal of geophysical research. Space physics 2019-03, Vol.124 (3), p.1475-1490
• Main Authors: Henri, P., Sgattoni, A., Briand, C., Amiranoff, F., Riconda, C.
• Format: Article
• Language: English
• Subjects: Astrophysics; Computer simulation; Coronal mass ejection; Diagnostic systems; Directivity; Electromagnetic radiation; Electron acceleration; Electron beams; Emissions; Energy conversion efficiency; In situ measurement; Kinetic energy; Parameters; Photovoltaic cells; Physics; Plasma frequencies; Plasma instabilities; Radio emission; Radio waves; Remote observing; Sciences of the Universe; Solar and Stellar Astrophysics; Solar corona; Solar flares; Solar wind; Space Physics; Wave interaction
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2018JA025707

Solar radio emissions are electromagnetic waves emitted in the solar wind as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as interplanetary coronal mass ejections. Different physical mechanisms have been suggested to describe their origin. A good understanding of the emission process would enable to infer the kinetic energy transferred from accelerated electrons to radio waves. Even if the electrostatic case has been extensively studied, full electromagnetic simulations were attempted only recently. In this work, we report large‐scale 2D3V electromagnetic particle‐in‐cell simulations that enable to identify the generation of both electrostatic and electromagnetic waves originated by a succession of plasma instabilities. They confirm that an efficient mechanism to generate solar radio emissions close to T2f, the harmonic of the plasma frequency, is a multistage model based on a succession of nonlinear three‐wave interaction processes. Through a parametric study of the electron beam parameters, we show that (i) the global efficiency of the multistep conversion mechanism from the electron beam kinetic energy to the T2f radio wave is independent of the beam parameters, approximately 10−5 in all tested configurations, while (ii) the directivity of the electromagnetic radio wave strongly depends on the origin electron beam. Those results represent a step forward toward the use of solar wind radio emissions, observed remotely, as a diagnostic for the properties of the electron beam located at the source of the radio emission, and therefore to eventually better characterize remotely electron acceleration mechanisms in space regions not directly accessible to in situ measurements. Key Points We single out the successive steps of the generation mechanisms of solar radio emissions We quantify the energy transferred from energetic particles to radio waves and show it is independent of energetic particles parameters We identify the directivity of the radio emissions and show its strong dependence on energetic particles parameters.