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1. Detection of small magnetic flux ropes from the third and fourth Parker Solar Probe encounters

   https://doi.org/10.1051/0004-6361/202039298  

   Zhao, L.-L.; Zank, G. P.; Hu, Q.; Telloni, D.; Chen, Y.; Adhikari, L.; Nakanotani, M.; Kasper, J. C.; Huang, J.; Bale, S. D.; et al (June 2021, Astronomy & Astrophysics)

   null (Ed.)

   Context. Aims. We systematically search for magnetic flux rope structures in the solar wind to within the closest distance to the Sun of ~0.13 AU, using data from the third and fourth orbits of the Parker Solar Probe. Methods. We extended our previous magnetic helicity-based technique of identifying magnetic flux rope structures. The method was improved upon to incorporate the azimuthal flow, which becomes larger as the spacecraft approaches the Sun. Results. A total of 21 and 34 magnetic flux ropes are identified during the third (21-day period) and fourth (17-day period) orbits of the Parker Solar Probe, respectively. We provide a statistical analysis of the identified structures, including their relation to the streamer belt and heliospheric current sheet crossing. 

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2. Magnetohydrodynamic Simulation of a Coronal Mass Ejection Observed during the Near-radial Alignment of Solar Orbiter and Earth

   https://doi.org/10.3847/1538-4357/adb1ac  

   Singh, Talwinder; Hegde, Dinesha V; Kim, Tae K; Pogorelov, Nikolai V (February 2025, The Astrophysical Journal)

   Abstract Interplanetary coronal mass ejections (ICMEs) are the primary sources of geomagnetic storms at Earth. The negative out-of-ecliptic component (B_z) of magnetic field in the ICME or its associated sheath region is necessary for it to be geoeffective. For this reason, magnetohydrodynamic simulations of CMEs containing data-constrained flux ropes are more suitable for forecasting their geoeffectiveness as compared to hydrodynamic models of the CME. ICMEs observed in situ by radially aligned spacecraft can provide an important setup to validate the physics-based heliospheric modeling of CMEs. In this work, we use the constant-turn flux rope (CTFR) model to study an ICME that was observed in situ by Solar Orbiter (SolO) and at Earth, when they were in a near-radial alignment. This was a stealth CME that erupted on 2020 April 14 and reached Earth on 2020 April 20 with a weak shock and a smoothly rotating magnetic field signature. We found that the CTFR model was able to reproduce the rotating magnetic field signature at both SolO and Earth with very good accuracy. The simulated ICME arrived 5 hr late at SolO and 5 hr ahead at Earth, when compared to the observed ICME. We compare the propagation of the CME front through the inner heliosphere using synthetic J-maps and those observed in the heliospheric imager data and discuss the role of incorrect ambient solar wind background on kinematics of the simulated CME. This study supports the choice of the CTFR model for reproducing the magnetic field of ICMEs. 

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3. Solar Orbiter observations of an ion-scale flux rope confined to a bifurcated solar wind current sheet

   https://doi.org/10.1051/0004-6361/202140949  

   Eastwood, J. P.; Stawarz, J. E.; Phan, T. D.; Laker, R.; Robertson, S.; Zhao, L.-L.; Zank, G. P.; Lavraud, B.; Shay, M. A.; Evans, V.; et al (December 2021, Astronomy & Astrophysics)

   Context. Flux ropes in the solar wind are a key element of heliospheric dynamics and particle acceleration. When associated with current sheets, the primary formation mechanism is magnetic reconnection and flux ropes in current sheets are commonly used as tracers of the reconnection process. Aims. Whilst flux ropes associated with reconnecting current sheets in the solar wind have been reported, their occurrence, size distribution, and lifetime are not well understood. Methods. Here we present and analyse new Solar Orbiter magnetic field data reporting novel observations of a flux rope confined to a bifurcated current sheet in the solar wind. Comparative data and large-scale context is provided by Wind. Results. The Solar Orbiter observations reveal that the flux rope, which does not span the current sheet, is of ion scale, and in a reconnection formation scenario, existed for a prolonged period of time as it was carried out in the reconnection exhaust. Wind is also found to have observed clear signatures of reconnection at what may be the same current sheet, thus demonstrating that reconnection signatures can be found separated by as much as ∼2000 Earth radii, or 0.08 au. Conclusions. The Solar Orbiter observations provide new insight into the hierarchy of scales on which flux ropes can form, and show that they exist down to the ion scale in the solar wind. The context provided by Wind extends the spatial scale over which reconnection signatures have been found at solar wind current sheets. The data suggest the local orientations of the current sheet at Solar Orbiter and Wind are rotated relative to each other, unlike reconnection observed at smaller separations; the implications of this are discussed with reference to patchy vs. continuous reconnection scenarios. 

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4. Magnetic flux rope: What is it?

   https://doi.org/10.1088/1742-6596/2544/1/012002  

   Hu, Qiang (July 2023, Journal of Physics: Conference Series)

   Abstract Magnetic flux rope, a type of magnetic field structure in space plasmas, has been studied for decades through both observational and theoretical means. We provide a brief report on our recent modeling study of its magnetic field configuration based on in-situ spacecraft measurements, focusing on those made for large-scale flux ropes in the interplanetary space. We illustrate the complexity in its field-line topology by presenting two event studies employing a unique analysis method. In particular, we demonstrate the feasibility and challenges for the approach to use two or more in-situ spacecraft datasets. We discuss the implications of our results and offer some thoughts on further advancing the investigation of the nature of the magnetic flux rope. 

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5. Characterization of Magnetic Flux Contents for Two Flux Transfer Events From Both In Situ and Ionospheric Observations

   https://doi.org/10.1029/2023JA032088  

   Wang, Shuo; Zou, Ying; Hu, Qiang; Shi, Xueling; Hasegawa, Hiroshi (February 2024, Journal of Geophysical Research: Space Physics)

   Abstract Flux transfer events (FTEs) are a type of magnetospheric phenomena that exhibit distinctive observational signatures from the in situ spacecraft measurements. They are generally believed to possess a magnetic field configuration of a magnetic flux rope and formed through magnetic reconnection at the dayside magnetopause, sometimes accompanied with enhanced plasma convection in the ionosphere. We examine two FTE intervals under the condition of southward interplanetary magnetic field (IMF) with a dawn‐dusk component. We apply the Grad‐Shafranov (GS) reconstruction method to the in situ measurements by the Magnetospheric Multiscale (MMS) spacecraft to derive the magnetic flux contents associated with the FTE flux ropes. In particular, given a cylindrical magnetic flux rope configuration derived from the GS reconstruction, the magnetic flux content can be characterized by both the toroidal (axial) and poloidal fluxes. We then estimate the amount of magnetic flux (i.e., the reconnection flux) encompassed by the area “opened” in the ionosphere, based on the ground‐based Super Dual Auroral Radar Network (SuperDARN) observations. We find that for event 1, the FTE flux rope is oriented in the approximate dawn‐dusk direction, and the amount of its total poloidal magnetic flux falls within the range of the corresponding reconnection flux. For event 2, the FTE flux rope is oriented in the north‐south direction. Both the FTE flux and the reconnection flux have greater uncertainty. We provide a detailed description about a formation scenario of sequential magnetic reconnection between adjacent field lines based on the FTE flux rope configurations from our results. 

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