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Die Quellen von weit-ausgebreiteten solaren energiereichen Teilchen-Ereignissen - Ein umfassender Ansatz, der Modellierung und Beobachtung kombiniert

Antragsteller Professor Dr. Bernd Heber, seit 1/2021
Fachliche Zuordnung Astrophysik und Astronomie
Kern- und Elementarteilchenphysik, Quantenmechanik, Relativitätstheorie, Felder
Förderung Förderung von 2018 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 399903456
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

The main mechanisms that produce SEE events, which spread over broad longitudinal distances in interplanetary space, are still under discussion and subject to intensive research. We refer to them as widespread SEE events. The objective of our project is to combine extensive particle transport modeling with detailed analysis of spacecraft observations to infer the physical processes under discussion. This approach allows us to test different potential scenarios that are i) a wide particle injection region close to the Sun and ii) a transport mechanism that distributes particles perpendicular to the mean IMF. Most likely, a combination of these processes is required to explain the observation over large distances, which can also be tested by our approach. The launch of SolO in combination with existing spacecraft Wind and STEREO-A has opened up new possibilities for the study of widespread SEE events. In the time period from February 2020 to June 2022, we identified 18 time periods for which a significant particle increase could be observed for SolO and STEREO-A or Wind. However, only ten of these events show widespread characteristics and fulfill the requirements for our transport modeling, e.g., an unambiguous source location could be identified. For the purpose of our extensive transport modeling, a two-dimensional transport equation is solved numerically. For the numerical implementation, we adopt a SDE scheme, because the ”classical” finite difference implementation produces large uncertainties. For the comparison of transport simulation and observation, commonly the zero’th and first moment of particle populations with respect to the magnetic field, referred to as pitch-angle distributions, are determined. However, we could show that these moments strongly depend on the limitation in the pitch-angle coverage for particle telescopes with only four fixed viewing directions, such as the STEREO SEPT and SolO EPT. This limitation makes the original approach questionable. Thus, we adopt the method suggested by Agueda et al. [2009] combining the modeling with a suitable model of the measuring process of the corresponding instrument to allow for meaningful comparison of transport simulation and measurements. This method is based on so-called Green’s functions of the two-dimensional transport model, a forward convolution of these Green’s functions with the particle injection functions, and a minimization with respect to the observations. Our automized Green’s function minimization implementation usually takes 30 to 120 minutes to obtain the likeliest transport simulation with respect to the observation, and the assumptions of the model. Because this procedure only had previously only been implemented for a one-dimensional transport model, our implementation for a two-dimensional transport model opens up new possibilities for SEE event studies involving transport modeling in the future. We validate our transport modeling scheme by applying it to a previously analyzed combined transport modeling approach of the widespread electron event on 14 August 2010 in Dröge et al. [2016] and obtain very similar results to their transport modeling. We applied our transport modeling scheme to three widespread events of our event list. For the event on 28 October 2021 our transport modeling scheme does obtain a set of transport parameters that is in decent agreement with the general features of the observation. Thus, we conclude that for the widespread event on 28 October 2021 a combination of particles escaping the Sun over a larger longitudinal region with a standard deviation of 22◦ , and an efficient transport perpendicular with a relative strength α = 0.1 with respect to the radial mean free path λr = 0.05 AU to the IMF are present. For the events on 22 and 28 May in 2021, the results of our transport modeling scheme did not reproduce the most important observational features. Potentially, because the assumptions made in our transport model are too simplistic. Thus, for these events, we can not conclude any information on the source of the widespread observation.

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