The sources of widespread solar energetic particle events - A comprehensive combined modeling and observational approach

• Applicant: Professor Dr. Bernd Heber, since 1/2021
• Subject Area: Astrophysics and Astronomy ; Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 399903456

Solar Energetic Particle (SEP) are accelerated by magnetic reconnection processes at the Sun and/or by shocks. A subgroup of these SEP events are the so-called widespread events which show extremely wide longitudinal particle spreads in the heliosphere up to 360 degrees. Because of their wide particle distributions, up to longitudes far separated from the parent activity regions at the Sun, these events are of special interest in terms of space weather and the underlying processes need to be identified. Different mechanisms are under discussion: On the one hand, the particle transport, i.e. strong perpendicular diffusion during the outward propagation of the particles may be responsible for the wide spreads. On the other hand, a large injection region, e.g. a wide range, over which the particles enter the open magnetic field regime of the interplanetary medium, could be the reason. Such a large injection region could point to specific magnetic field configurations, however, a larger acceleration region such as a shock would serve as well. As large SEP events often show not only a solar flare but also an accompanying Coronal Mass Ejection (CME), which can drive a shock, such a large acceleration region, apart from the point-like flaring region, might be present. In-situ measurements of SEP events are recorded by a fleet of spacecraft, e.g. situated in the Earth's orbit. To infer the acceleration and injection processes, multi-wavelength remote-sensing observations are employed. To bridge the gap between the injection sites and the in-situ measurements, transport models are used which characterize the particle propagation. As each SEP event is determined by the interplay of acceleration, injection, and transport processes, respectively, a comprehensive and combined analysis is needed to disentangle the different ingredients and to identify the drivers of the extraordinary wide particle spreads. In the proposed study we will focus on near-relativistic widespread electron events observed at 1 AU simultaneously close to Earth as well as at the two STEREO spacecraft. We will use a state of the art transport model to reproduce the multi-spacecraft observations of specific widespread events. By employing a combined observational and modeling approach we will identify the main drivers of the wide spreads for each analyzed event. Furthermore, we investigate if a point source together with strong perpendicular transport can explain such observations or if a certain width of the injection region is needed for all of these extreme events. Finally, we will analyze if different types of widespread events exist or if always a combination of certain processes must be involved.

• DFG Programme: Research Grants
• International Connection: South Africa, Switzerland
• Co-Investigator: Dr. Andreas Klassen
• Cooperation Partners: Dr. Frederic Effenberger; Ruhann Steyn; Professor Dr. Roelf Du Toit Strauss
• Ehemalige Antragstellerin: Dr. Nina Gieseler, until 12/2020