Browsing by Author "Monstein, Christian"
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- ItemCoronal Conditions for the Occurrence of Type II Radio Bursts(London : Institute of Physics Publ., 2021) Kouloumvakos, Athanasios; Rouillard, Alexis; Warmuth, Alexander; Magdalenic, Jasmina; Jebaraj, Immanuel. C.; Mann, Gottfried; Vainio, Rami; Monstein, ChristianType II radio bursts are generally observed in association with flare-generated or coronal-mass-ejection-driven shock waves. The exact shock and coronal conditions necessary for the production of type II radio emission are still under debate. Shock waves are important for the acceleration of electrons necessary for the generation of the radio emission. Additionally, the shock geometry and closed field line topology, e.g., quasi-perpendicular shock regions or shocks interacting with streamers, play an important role for the production of the emission. In this study we perform a 3D reconstruction and modeling of a shock wave observed during the 2014 November 5 solar event. We determine the spatial and temporal evolution of the shock properties and examine the conditions responsible for the generation and evolution of type II radio emission. Our results suggest that the formation and evolution of a strong, supercritical, quasi-perpendicular shock wave interacting with a coronal streamer were responsible for producing type II radio emission. We find that the shock wave is subcritical before and supercritical after the start of the type II emission. The shock geometry is mostly quasi-perpendicular throughout the event. Our analysis shows that the radio emission is produced in regions where the supercritical shock develops with an oblique to quasi-perpendicular geometry.
- ItemIdentifying the energy release site in a solar microflare with a jet(Les Ulis : EDP Sciences, 2023) Battaglia, Andrea Francesco; Wang, Wen; Saqri, Jonas; Podladchikova, Tatiana; Veronig, Astrid M.; Collier, Hannah; Dickson, Ewan C. M.; Podladchikova, Olena; Monstein, Christian; Warmuth, Alexander; Schuller, Frédéric; Harra, Louise; Krucker, SämContext. One of the main science questions of the Solar Orbiter and Parker Solar Probe missions deals with understanding how electrons in the lower solar corona are accelerated and how they subsequently access interplanetary space. Aims. We aim to investigate the electron acceleration and energy release sites as well as the manner in which accelerated electrons access the interplanetary space in the case of the SOL2021-02-18T18:05 event, a GOES A8 class microflare associated with a coronal jet. Methods. This study takes advantage of three different vantage points, Solar Orbiter, STEREO-A, and Earth, with observations drawn from eight different instruments, ranging from radio to X-ray. Multi-wavelength timing analysis combined with UV/EUV imagery and X-ray spectroscopy by Solar Orbiter/STIX (Spectrometer/Telescope for Imaging X-rays) is used to investigate the origin of the observed emission during different flare phases. Results. The event under investigation satisfies the classical picture of the onset time of the acceleration of electrons coinciding with the jet and the radio type III bursts. This microflare features prominent hard X-ray (HXR) nonthermal emission down to at least 10 keV and a spectrum that is much harder than usual for a microflare with γ = 2.9 ± 0.3. From Eartha's vantage point, the microflare is seen near the limb, revealing the coronal energy release site above the flare loop in EUV, which, from STIX spectroscopic analysis, turns out to be hot (i.e., at roughly the same temperature of the flare). Moreover, this region is moving toward higher altitudes over time (∼30akmas-1). During the flare, the same region spatially coincides with the origin of the coronal jet. Three-dimensional (3D) stereoscopic reconstructions of the propagating jet highlight that the ejected plasma moves along a curved trajectory. Conclusions. Within the framework of the interchange reconnection model, we conclude that the energy release site observed above-The-loop corresponds to the electron acceleration site, corroborating that interchange reconnection is a viable candidate for particle acceleration in the low corona on field lines open to interplanetary space.