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Plasmas are ubiquitous in the universe where most matter is in such a state, constituting stars, the interplanetary, interstellar and intergalactic medium, nebulae, and so forth. In the solar system for instance, a plasma sphere (the Sun) continuously ejects into the interplanetary medium a plasma (the solar wind) that interacts with the plasma (magnetospheres) surrounding the Earth or other planets. This makes the near-Earth environment a perfect astrophysical laboratory to study space plasmas. In plasma physics, magnetic reconnection is a fundamental process omnipresent in astrophysical systems. This unique mechanism converts magnetic energy into kinetic and thermal energy at kinetic scales, accelerating and heating the plasma while allowing a global reconfiguration of the magnetic topology. Spectacularly, changes induced on microscopic scales lead for instance to the drastic large-scale remodeling of a planet's or a star's magnetic field. In the past decades, various space missions have been launched to investigate the in-situ properties of astrophysical plasmas in the Sun-Earth environment, as well as to study the process of magnetic reconnection. They were equipped to unveil new features of their surrounding media, and in that they succeeded, particularly in bringing to light structures that were not observed before, either due to a lack of instrumental resolution or to the absence of previous data. In this manuscript, we focus on structures observed at the Earth's magnetopause and in the solar wind, and of significant importance to the dynamics of their environment. In our approach, we aim to shed light on the physical processes at stake for the formation of these structures, using modeling and statistical analysis to infer their properties and potential formation models. In the first part of the manuscript, we present the investigation of a type of coherent magnetic structure often observed traveling along the Earth's magnetopause and carrying a significant amount of energy, called Flux Transfer Events (FTE). Particularly, a new type of FTE was observed with magnetic reconnection resolved in its core. Such a signature questions the usual model put forward to explain the internal structure of FTEs. Through a statistical analysis of FTE, we were able to better understand their magnetic topology and determine the factors playing a role in their occurrence, gaining insights on how they may be produced through magnetic reconnection at the dayside magnetopause. We also report on observations of similar structures in the solar wind, underlining that the process at work at the magnetopause is probably occurring in the solar wind as well. In the second part of the manuscript, we move from the near-Earth environment to the inner heliosphere, focusing on magnetic switchbacks that are a key feature of the near-Sun solar wind. Magnetic switchbacks are deflections of the magnetic field, sometimes reversing the radial component of the field, and made of accelerated plasma relative to the background solar wind. Through a systematic study of their characteristic scales and orientation, we highlight that switchbacks are probably linked to solar surface features like granulation and supergranulation, and we show that their properties are consistent with a formation through the process of interchange reconnection in the low solar atmosphere. Magnetic reconnection is a common thread of this work, being ubiquitous at the Earth's magnetopause and in the solar wind, and most probably involved in the formation of switchbacks in the low corona as well. In the last part of the manuscript, we describe a new promising approach, based on visual identification, that permits to automatically detect magnetic reconnection exhausts in-situ in the solar wind. An automated detection algorithm may lead to large statistical analysis of reconnection jets in the solar wind, a significant step forward in understanding the process of magnetic reconnection., En physique des plasmas, la reconnexion magnétique est un processus fondamental, omniprésent dans les systèmes astrophysiques. Ce mécanisme remarquable convertit l'énergie magnétique en énergie cinétique et thermique sur des échelles cinétiques, de ce fait accélérant et chauffant le plasma tout en permettant une reconfiguration globale de la topologie du champ magnétique. De façon spectaculaire, les changements induits à l'échelle microscopique conduisent, par exemple, à un remodelage complet et à grande échelle du champ magnétique d'une planète ou d'une étoile. De par son accessibilité, l'environnement proche de la Terre est un parfait laboratoire astrophysique pour étudier les plasmas spatiaux. Ces dernières années, de nombreuses missions spatiales ont été lancées pour étudier les propriétés in situ des plasmas dans l'environnement Soleil-Terre, ainsi que le processus de reconnexion magnétique. Equipées pour dévoiler de nouvelles caractéristiques sur ces milieux, elles ont notamment mis en lumière des structures qui n'avaient pas été observées auparavant de part une résolution instrumentale insuffisante ou une absence de données antérieures. Ce manuscrit se concentre sur des structures observées à la magnétopause terrestre d'une part et dans le vent solaire d'autre part, et qui ont un impact significatif sur leur environnement. Notre approche a pour but d'expliquer les processus de formation en jeu pour ces structures à travers des études statistiques. Dans une première partie, nous étudions des structures magnétiques qui se propagent le long de la magnétopause terrestre, transportant des quantités importantes d'énergie et appelées Evènements de Transfert de Flux (FTE). Plus particulièrement, des FTE d'un nouveau genre ont été observées ces dernières années, présentant une signature de reconnexion magnétique en leur centre. Une telle observation remet en cause les modèles classiquement mis en avant pour expliquer leur structure interne. A travers une étude statistique des FTEs, nous avons pu mieux comprendre leur topologie magnétique et déterminer les facteurs environnementaux jouant un rôle dans leur apparition. Ces analyses nous renseignent sur les mécanismes de formation des FTE qui implique le processus de reconnexion magnétique sur le côté jour de la magnétopause. Nous présentons également des observations de structures similaires dans le vent solaire, soulignant que le processus en jeu à la magnétopause terrestre est probablement également à l'œuvre dans le vent solaire. Dans une seconde partie, nous passons de l'environnement terrestre à l'héliosphère interne, où les switchbacks magnétiques sont omniprésents dans le vent solaire proche du Soleil. Les switchbacks sont des déflections du champs magnétique qui vont jusqu'à renverser sa composante radiale, et qui sont de plus accélérées par rapport au vent solaire de fond. A travers une étude systématique de leurs échelles caractéristiques ainsi que de leur orientation, nous montrons que les switchbacks sont probablement liés à des structures de surfaces tels que la granulation ou la supergranulation. Nous concluons que leurs propriétés sont cohérentes avec une formation dans la basse atmosphère à travers le processus de reconnexion d'interchange. La reconnexion magnétique est un fil conducteur dans ce travail, omniprésente à la magnétopause terrestre et dans le vent solaire, et menant à la formation de structures impactant significativement leur environnement. Dans la dernière partie du manuscrit, nous présentons une nouvelle méthode prometteuse de détection automatique des signatures de jets de reconnexion, inspirée du processus d'identification visuelle de ces jets. Un tel algorithme de détection automatique permet d'envisager des études statistiques de jets de reconnexion observés dans le vent solaire, ce qui serait une avancée importante dans la compréhension du phénomène de la reconnexion magnétique.

Context. Solar Orbiter, the new-generation mission dedicated to solar and heliospheric exploration, was successfully launched on February 10, 2020, 04:03 UTC from Cape Canaveral. During its first perihelion passage in June 2020, two successive interplanetary coronal mass ejections (ICMEs), propagating along the heliospheric current sheet (HCS), impacted the spacecraft. Aims. This paper addresses the investigation of the ICMEs encountered by Solar Orbiter on June 7−8, 2020, from both an observational and a modeling perspective. The aim is to provide a full description of those events, their mutual interaction, and their coupling with the ambient solar wind and the HCS. Methods. Data acquired by the MAG magnetometer, the Energetic Particle Detector suite, and the Radio and Plasma Waves instrument are used to provide information on the ICMEs’ magnetic topology configuration, their magnetic connectivity to the Sun, and insights into the heliospheric plasma environment where they travel, respectively. On the modeling side, the Heliospheric Upwind eXtrapolation model, the 3D COronal Rope Ejection technique, and the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) tool are used to complement Solar Orbiter observations of the ambient solar wind and ICMEs, and to simulate the evolution and interaction of the ejecta in the inner heliosphere, respectively. Results. Both data analysis and numerical simulations indicate that the passage of two distinct, dynamically and magnetically interacting (via magnetic reconnection processes) ICMEs at Solar Orbiter is a possible scenario, supported by the numerous similarities between EUHFORIA time series at Solar Orbiter and Solar Orbiter data. Conclusions. The combination of in situ measurements and numerical simulations (together with remote sensing observations of the corona and inner heliosphere) will significantly lead to a deeper understanding of the physical processes occurring during the CME-CME interaction.

Context. Prominence eruptions provide key observations to understand the launch of coronal mass ejections as their cold plasma traces a part of the unstable magnetic configuration. Aims. We select a well observed case to derive observational constraints for eruption models. Methods. We analyze the prominence eruption and loop expansion and contraction observed on 02 March 2015 associated with a GOES M3.7 class flare (SOL2015-03-02T15:27) using the data from Atmospheric Imaging Assembly (AIA) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We study the prominence eruption and the evolution of loops using the time-distance techniques. Results. The source region is a decaying bipolar active region where magnetic flux cancellation is present for several days before the eruption. AIA observations locate the erupting prominence within a flux rope viewed along its local axis direction. We identify and quantify the motion of loops in contraction and expansion located on the side of the erupting flux rope. Finally, RHESSI hard X-ray observations identify the loop top and two foot-point sources. Conclusions. Both AIA and RHESSI observations support the standard model of eruptive flares. The contraction occurs 19 minutes after the start of the prominence eruption indicating that this contraction is not associated with the eruption driver. Rather, this prominence eruption is compatible with an unstable flux rope where the contraction and expansion of the lateral loop is the consequence of a side vortex developing after the flux rope is launched., Comment: 16 pages, 9 figures, 1 table, and appendix

Context. Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs). One property of MCs is the presence of a magnetic flux rope. Is the difference between ICMEs with and without MCs intrinsic or rather due to an observational bias? Aims. As the spacecraft has no relationship with the MC trajectory, the frequency distribution of MCs versus the spacecraft distance to the MCs’ axis is expected to be approximately flat. However, Lepping & Wu (2010, Ann. Geophys., 28, 1539) confirmed that it is a strongly decreasing function of the estimated impact parameter. Is a flux rope more frequently undetected for larger impact parameter? Methods. In order to answer the questions above, we explore the parameter space of flux rope models, especially the aspect ratio, boundary shape, and current distribution. The proposed models are analyzed as MCs by fitting a circular linear force-free field to the magnetic field computed along simulated crossings. Results. We find that the distribution of the twist within the flux rope and the non-detection due to too low field rotation angle or magnitude only weakly affect the expected frequency distribution of MCs versus impact parameter. However, the estimated impact parameter is increasingly biased to lower values as the flux rope cross section is more elongated orthogonally to the crossing trajectory. The observed distribution of MCs is a natural consequence of a flux rope cross section flattened on average by a factor 2 to 3 depending on the magnetic twist profile. However, the faster MCs at 1 AU, with V > 550 km s-1, present an almost uniform distribution of MCs vs. impact parameter, which is consistent with round-shaped flux ropes, in contrast with the slower ones. Conclusions. We conclude that the sampling of MCs at various distances from the axis does not significantly affect their detection. The large part of ICMEs without MCs could be due to a too strict criteria for MCs or to the fact that these ICMEs are encountered outside their flux rope or near the leg region, or they do not contain a flux rope. Fil: Démoulin, Pascal. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia Fil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Janvier, M.. Centre National de la Recherche Scientifique. Observatoire de Paris; Francia