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Current Sheets, Plasmoids and Flux Ropes in the Heliosphere: Part I. 2-D or not 2-D? General and Observational Aspects

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Olga V. Khabarova at Tel Aviv University
Olga V. Khabarova
O. Malandraki at National Observatory of Athens
O. Malandraki
H. V. Malova at Lomonosov Moscow State University
H. V. Malova
Roman Anatolevich Kislov at Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation
Roman Anatolevich Kislov
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Abstract and Figures

Recent accumulation of a critical mass of observational material from different spacecraft complete with the enhanced abilities of numerical methods have led to a boom of studies revealing the high complexity of processes occurring in the heliosphere. Views on the solar wind filling the interplanetary medium have dramatically developed from the beginning of the space era. A 2-D picture of the freely expanding solar corona and non-interacting solar wind structures described as planar or spherically-symmetric objects has dominated for decades. Meanwhile, the scientific community gradually moved to a modern understanding of the importance of the 3-D nature of heliospheric processes and their studies via MHD/kinetic simulations, as well as observations of large-scale flows and streams both in situ and remotely, in white light and/or via interplanetary scintillations. The new 3-D approach has provided an opportunity to understand the dynamics of heliospheric structures and processes that could not even be imagined before within the 2-D paradigm. In this review, we highlight a piece of the puzzle, showing the evolution of views on processes related to current sheets, plasmoids, blobs and flux ropes of various scales and origins in the heliosphere. The first part of the review focuses on introducing these plasma structures, discussing their key properties, and paying special attention to their observations in different space plasmas.
Example of an uncomplicated crossing of a current sheet identified from the plasma and IMF data with a minute resolution observed by the Wind spacecraft at 1 AU on June 25, 2004. 1-minute resolution data from the WIND spacecraft are used. The HCS is shown by the pink stripe. From top to bottom: the IMF strength (B\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B$\end{document}), the horizontal Earth-Sun-aligned IMF component (Bx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{x}$\end{document}), the azimuthal angle of the IMF (Bphi\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{phi}$\end{document}), the solar wind speed (V), the solar wind density (Np), and the plasma beta (the ratio of the plasma pressure to the magnetic field pressure). A classic HCS crossing is identified with the depression in the total B\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B$\end{document} since at least one IMF component becomes zero at the neutral line (in the particular case it is Bx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{x}$\end{document}), the increase in Np, and the increase in the plasma beta are observed at the HCS position. Arrows show dynamics of the corresponding parameters at the current sheet. Typical signatures are as follows: the IMF strength drops, at least one of IMF components crosses zero value, the azimuthal IMF angle and/or clock angle change sharply, the solar wind density and the plasma beta increase sharply, while the solar wind speed may not change. The event is discussed in Zharkova and Khabarova (2012)
Example of an uncomplicated crossing of a current sheet identified from the plasma and IMF data with a minute resolution observed by the Wind spacecraft at 1 AU on June 25, 2004. 1-minute resolution data from the WIND spacecraft are used. The HCS is shown by the pink stripe. From top to bottom: the IMF strength (B\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B$\end{document}), the horizontal Earth-Sun-aligned IMF component (Bx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{x}$\end{document}), the azimuthal angle of the IMF (Bphi\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{phi}$\end{document}), the solar wind speed (V), the solar wind density (Np), and the plasma beta (the ratio of the plasma pressure to the magnetic field pressure). A classic HCS crossing is identified with the depression in the total B\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B$\end{document} since at least one IMF component becomes zero at the neutral line (in the particular case it is Bx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$B_{x}$\end{document}), the increase in Np, and the increase in the plasma beta are observed at the HCS position. Arrows show dynamics of the corresponding parameters at the current sheet. Typical signatures are as follows: the IMF strength drops, at least one of IMF components crosses zero value, the azimuthal IMF angle and/or clock angle change sharply, the solar wind density and the plasma beta increase sharply, while the solar wind speed may not change. The event is discussed in Zharkova and Khabarova (2012)
… 
Stochastic or turbulent magnetic reconnection and reconnection-borne magnetic islands. a) Results of modeling of a reconnecting current sheet affected by turbulence in the presence of the guide field directed perpendicular to the page (adapted from Lazarian et al. 2012 and Kowal et al. 2012). Left panel: magnetic field lines of the opposite direction (shown by blue and red colors) beginning to reconnect stochastically in many places. Central panel: intensity of the electric current (blue – minimal, and yellow – maximal) at the stage of the developed reconnection. Direction of the magnetic field lines is shown by small arrows. Right panel: Magnetic field at the reconnecting current sheet; corresponds to the middle panel. b) 2.5-dimensional fully kinetic implicit particle-in-cell (PIC) simulations explaining observations of magnetic islands and reconnecting current sheets in the solar wind (adapted from Eriksson et al. 2014). Simulations are made in the right handed orthogonal MNL system (M=N×L\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\text{M} = \text{N} \times \text{L}$\end{document}). From top to bottom: out-of-plane (M-component) magnetic field relative to a background finite guide field; L-component of the normalized ion velocity; L-component of the normalized electron velocity; Relative ion density. c) Sketch illustrating the presence of numerous reconnecting small-scale magnetic islands in the 2-D cut perpendicular the HCS. Adapted from Adhikari et al. (2019)
Stochastic or turbulent magnetic reconnection and reconnection-borne magnetic islands. a) Results of modeling of a reconnecting current sheet affected by turbulence in the presence of the guide field directed perpendicular to the page (adapted from Lazarian et al. 2012 and Kowal et al. 2012). Left panel: magnetic field lines of the opposite direction (shown by blue and red colors) beginning to reconnect stochastically in many places. Central panel: intensity of the electric current (blue – minimal, and yellow – maximal) at the stage of the developed reconnection. Direction of the magnetic field lines is shown by small arrows. Right panel: Magnetic field at the reconnecting current sheet; corresponds to the middle panel. b) 2.5-dimensional fully kinetic implicit particle-in-cell (PIC) simulations explaining observations of magnetic islands and reconnecting current sheets in the solar wind (adapted from Eriksson et al. 2014). Simulations are made in the right handed orthogonal MNL system (M=N×L\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\text{M} = \text{N} \times \text{L}$\end{document}). From top to bottom: out-of-plane (M-component) magnetic field relative to a background finite guide field; L-component of the normalized ion velocity; L-component of the normalized electron velocity; Relative ion density. c) Sketch illustrating the presence of numerous reconnecting small-scale magnetic islands in the 2-D cut perpendicular the HCS. Adapted from Adhikari et al. (2019)
… 
Evolution of a prominence in the solar corona. a) Twisted and swirled flux rope observed during the course of M 3.6 class on February 24, 2011. Six snapshots from SDO AIA 304 Angstrom taken from 07:28:20 UT to 07:33:32 UT are available as a movie on https://helioviewer.org/. b) 3-D numerical reconstructions of magnetic field lines forming an erupting flux rope, shown at different stages of the eruption process. Magnetic field intensity is indicated by color from deep blue (zero G) to red. There is a magnetic separator in the middle of the flux rope. c) The corresponding map of the vertical velocity. Adapted from Nishida et al. (2013)
Evolution of a prominence in the solar corona. a) Twisted and swirled flux rope observed during the course of M 3.6 class on February 24, 2011. Six snapshots from SDO AIA 304 Angstrom taken from 07:28:20 UT to 07:33:32 UT are available as a movie on https://helioviewer.org/. b) 3-D numerical reconstructions of magnetic field lines forming an erupting flux rope, shown at different stages of the eruption process. Magnetic field intensity is indicated by color from deep blue (zero G) to red. There is a magnetic separator in the middle of the flux rope. c) The corresponding map of the vertical velocity. Adapted from Nishida et al. (2013)
… 
Evolution of understanding of the 3-D nature of ICMEs and their substructure (in sketches). a) Illustration of views on a possible ICME structure (3-D version of Fig. 6 of Chen 2017 based on suggestions from Hundhausen 1999). Reflection of the prolonged discussion of 70th–90th of XX century: “Dome of twisted magnetic field lines vs loop”. Later, the loop was replaced with a twisted flux rope as shown in the right panel. b) Helicity of the ICME magnetic cloud suggested by McComas et al. (1992). c) Multiple ICMEs co-existing in the interplanetary space (adapted from Malandraki et al. 2000). In both cases b) and c) the magnetic cloud is suggested to be an elongated flux rope. d) Fragmentation of kinking, twisting and writhed flux ropes into smaller-scale plasmoids leads to formation of current sheets, plasmoids and magnetic reconnection within ICMEs. From left to right: a typical view on the ICME structure; fragmentation of the magnetic cloud; formation of plasmoids with a complex magnetic helicity separated by small-scale current sheets (grey). Large quasi-stable current sheet is formed between the ICME sheath and the main body of the ICME
Evolution of understanding of the 3-D nature of ICMEs and their substructure (in sketches). a) Illustration of views on a possible ICME structure (3-D version of Fig. 6 of Chen 2017 based on suggestions from Hundhausen 1999). Reflection of the prolonged discussion of 70th–90th of XX century: “Dome of twisted magnetic field lines vs loop”. Later, the loop was replaced with a twisted flux rope as shown in the right panel. b) Helicity of the ICME magnetic cloud suggested by McComas et al. (1992). c) Multiple ICMEs co-existing in the interplanetary space (adapted from Malandraki et al. 2000). In both cases b) and c) the magnetic cloud is suggested to be an elongated flux rope. d) Fragmentation of kinking, twisting and writhed flux ropes into smaller-scale plasmoids leads to formation of current sheets, plasmoids and magnetic reconnection within ICMEs. From left to right: a typical view on the ICME structure; fragmentation of the magnetic cloud; formation of plasmoids with a complex magnetic helicity separated by small-scale current sheets (grey). Large quasi-stable current sheet is formed between the ICME sheath and the main body of the ICME
… 
MHD modeling of propagation of ICMEs in the inner heliosphere. a) One of the pioneering 3-D MHD modeling of ICMEs (adapted from Kataoka et al. 2009). The complexity of magnetic field lines is shown in the ecliptic plane (the Earth’s position is X=215Rs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$X=215~R_{s}$\end{document}, where Rs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$R_{s}$\end{document} is the solar radius). b) Formation of a complex flux rope within an ICME impacted by Alfvenic turbulence (adapted from Manchester and Van Der Holst 2017). The 2-hour-after-launch snapshot. Solar wind speed values are shown by different colors. c) SUSANOO solar wind modeling applied to ICME propagation (adapted from Shiota and Kataoka 2016). The solar wind speed is plotted analogous to b) in the projection onto the ecliptic plane. Magnetic field lines are grey ropes. d) Fractalization and formation of current sheets and magnetic islands within a CME as modeled for 20 hours (left) and 21 hours (right) after shearing begins (adapted from Hosteaux et al. 2018). Magnetic field lines are black and the current density values correspond to the color scale shown in the upper part of the panels
+35
MHD modeling of propagation of ICMEs in the inner heliosphere. a) One of the pioneering 3-D MHD modeling of ICMEs (adapted from Kataoka et al. 2009). The complexity of magnetic field lines is shown in the ecliptic plane (the Earth’s position is X=215Rs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$X=215~R_{s}$\end{document}, where Rs\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$R_{s}$\end{document} is the solar radius). b) Formation of a complex flux rope within an ICME impacted by Alfvenic turbulence (adapted from Manchester and Van Der Holst 2017). The 2-hour-after-launch snapshot. Solar wind speed values are shown by different colors. c) SUSANOO solar wind modeling applied to ICME propagation (adapted from Shiota and Kataoka 2016). The solar wind speed is plotted analogous to b) in the projection onto the ecliptic plane. Magnetic field lines are grey ropes. d) Fractalization and formation of current sheets and magnetic islands within a CME as modeled for 20 hours (left) and 21 hours (right) after shearing begins (adapted from Hosteaux et al. 2018). Magnetic field lines are black and the current density values correspond to the color scale shown in the upper part of the panels
… 
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Space Sci Rev (2021) 217:38
https://doi.org/10.1007/s11214-021-00814-x
Current Sheets, Plasmoids and Flux Ropes
in the Heliosphere
Part I. 2-D or not 2-D? General and Observational Aspects
O. Khabarova1,2 ·O. Malandraki3·H. Malova2,4 ·R. Kislov2·A. Greco5·
R. Bruno6·O. Pezzi7,8,9 ·S. Servidio5·Gang Li10 ·W. Matthaeus11 ·
J. Le Roux10 ·N.E. Engelbrecht12 ·F. Pecora5·L. Zelenyi2·V. Ob ri d k o1·
V. Kuznetsov1
Received: 7 October 2020 / Accepted: 3 March 2021 / Published online: 23 March 2021
© The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract Recent accumulation of a critical mass of observational material from different
spacecraft complete with the enhanced abilities of numerical methods have led to a boom
of studies revealing the high complexity of processes occurring in the heliosphere. Views
on the solar wind filling the interplanetary medium have dramatically developed from the
beginning of the space era. A 2-D picture of the freely expanding solar corona and non-
interacting solar wind structures described as planar or spherically-symmetric objects has
dominated for decades. Meanwhile, the scientific community gradually moved to a modern
understanding of the importance of the 3-D nature of heliospheric processes and their studies
via MHD/kinetic simulations, as well as observations of large-scale flows and streams both
in situ and remotely, in white light and/or via interplanetary scintillations. The new 3-D
approach has provided an opportunity to understand the dynamics of heliospheric structures
O. Khabarova
habarova@izmiran.ru
1Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation
of the Russian Academy of Sciences (IZMIRAN), Moscow, 108840, Russia
2Space Research Institute (IKI) RAS, Moscow, 117997, Russia
3IAASARS, National Observatory of Athens, Penteli, Greece
4Scobeltsyn Nuclear Physics Institute of Lomonosov Moscow State University, Moscow, 119991,
Russia
5Dipartimento di Fisica, Università della Calabria, 87036 Rende (CS), Italy
6Istituto di Astrofisica e Planetologia Spaziali, Istituto Nazionale di Astrofisica (IAPS-INAF),
Roma, Italy
7Gran Sasso Science Institute (GSSI), Viale F. Crispi 7, 67100 L’Aquila, Italy
8INFN, Laboratori Nazionali del Gran Sasso (LNGS), 67100 Assergi, L’Aquila, Italy
9Istituto per la Scienza e Tecnologia dei Plasmi, CNR, Via Amendola 122/D, 70126 Bari, Italy
10 Center for Space Plasma and Aeronomic Research (CSPAR) and Department of Space Science,
University of Alabama in Huntsville, Huntsville, AL 35805, USA
11 Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
12 Centre for Space Research, North-West University, Potchefstroom, 2522, South Africa
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... This suggests the presence of a so-called zero magnetic field surface at the center of each current sheet. Current sheets generated by solar wind turbulence are typically small-scale and short-lived, whereas long-lived, large-scale current sheets are formed at the boundaries of high-speed streams and flows, as well as represent extensions of large-scale neutral lines of the solar magnetic field (see [15][16][17][18]). These discontinuities play a crucial role in solar wind dynamics by inducing instabilities and altering the magnetic field geometry. ...
... Reconnecting current sheets may contribute to plasma heating, particle acceleration, and the generation of waves and secondary coherent structures in their vicinity since current sheets are known to be sites where magnetic reconnection occurs, converting magnetic energy into the kinetic energy of charged particles. This process is considered as a key mechanism for heating and accelerating particles in the solar corona [35] and can similarly be applied to the solar wind [17,21,22]. Ongoing magnetic reconnection increases the turbulence level in the solar wind, which should be evident in the magnetic field spectra. ...
... As the ICME moves further into the solar wind, its parts become increasingly turbulent and intermittent, and the magnetic cloud undergoes internal magnetic reconnection, leading to the formation of more complex twisted flux rope structures. This process is often intensified by the interaction of the ICME with other flows, streams, and large-scale structures in the surrounding solar wind (see [17]). The final sketch on the right represents the state of the ICME as it is typically observed at 1 AU, characterized by significantly entangled flux ropes in a fragmented magnetic cloud, with several strong current sheets inside the ICME sheath. ...
Linking Turbulent Interplanetary Magnetic Field Fluctuations and Current Sheets
Article
Full-text available
  • Nov 2024
The study aims to understand the role of solar wind current sheets (CSs) in shaping the spectrum of turbulent fluctuations and driving dissipation processes in space plasma. Local non-adiabatic heating and acceleration of charged particles in the solar wind is one of the most intriguing challenges in space physics. Leading theories attribute these effects to turbulent heating, often associated with magnetic reconnection at small-scale coherent structures in the solar wind, such as CSs and flux ropes. We identify CSs observed at 1 AU in different types of the solar wind around and within an interplanetary coronal mass ejection (ICME) and analyze the corresponding characteristics of the turbulent cascade. It is found that the spectra of fluctuations of the interplanetary magnetic field may be reshaped due to the CS impact potentially leading to local disruptions in energy transfer along the cascade of turbulent fluctuations. Case studies of the spectra behavior at the peak of the CS number show their steepening at MHD scales, flattening at kinetic scales, and merging of the spectra into a single form, with the break almost disappearing. In the broader vicinity of the CS number peak, the behavior of spectral parameters changes sharply, but not always following the same pattern. The statistical analysis shows a clear correlation between the break frequency and the CS number. These results are consistent with the picture of turbulent reconnection at CSs. The CS occurrence is found to be statistically linked with the increased temperature. In the ICME sheath, there are two CS populations observed in the hottest and coldest plasma.
View
... Sometimes, the intricate configuration within an ICME's flux rope becomes distorted to the extent that it exhibits features like pancaking, writhe, or the formation of internal current sheets (Sturrock et al. 2001;Fan 2005;Török & Kliem 2005;Török et al. 2014;Shaikh et al. 2018Shaikh et al. , 2019Shaikh et al. , 2020Shaikh & Raghav 2022a, 2022bGhag et al. 2023Ghag et al. , 2024bRaghav et al. 2023b;Choraghe et al. 2023). These distortions may even culminate in the fragmentation of the flux rope into multiple large-scale plasmoids (Khabarova et al. 2021). ...
... In fact, this kind of wave has rarely been considered in the context of ICME magnetic clouds; hence, we still do not have adequate plasma observations at kinetic scales. Several studies, mostly numerical, have addressed this topic, suggesting that discontinuities and small-scale current sheets (Khabarova et al. 2021) that are candidates for reconnection events might be regions where dissipative phenomena are at work with consequent plasma heating and acceleration. To date, there have been no reports of the existence of KAWs within the ICME flux ropes featuring low plasma beta. ...
... The yellow-shaded portion indicates the current sheet crossover region. 2011 October 25) (Foullon et al. 2007;Owens 2009;Adhikari et al. 2019;Khabarova et al. 2021). In this context, to validate our findings, we conducted a comparative analysis using data derived from the WSA-ENLIL solar wind simulation. ...
Observation of Kinetic Alfvén Waves inside an Interplanetary Coronal Mass Ejection Magnetic Cloud at 1 au
Article
Full-text available
  • Apr 2024
  • ASTROPHYS J
Recent advancements have significantly enhanced our grasp of interplanetary coronal mass ejections (ICMEs) in the heliosphere. These observations have uncovered complex kinematics and structural deformations in ICMEs, hinting at the possible generation of magnetohydrodynamic (MHD) and kinetic-scale waves. While MHD-scale waves in magnetic clouds have been explored, understanding the dynamics of kinetic-scale mode waves remains challenging. This article demonstrates the first in situ observation of kinetic Alfvén waves (KAWs) within an ICME's magnetic cloud, notably near the heliospheric current sheet-ICME interaction region, close to the reconnection exhaust. Analysis indicates a distinctive negative bump in the estimated normalized magnetic helicity (σ m = −0.38) around the gyrofrequency spread, indicating a right-handed polarization of the wave. Furthermore, examination across flow angle (θ VB) within the frequency domain reveals a specific zone (90°-135°) showcasing negative helicity fluctuations, confirming the presence of KAWs. Moreover, we noted a significant rise in temperature anisotropy in the vicinity, indicating the role of KAWs in plasma heating. Identifying KAW challenges established notions about ordered magnetic clouds and raises questions about energy transfer processes within these structures. This finding opens the door to a deeper understanding of energy transfer mechanisms within traditionally nondissipative regions and invites further exploration of low-beta plasma heating and the interactions between waves and particles in magnetic clouds. Unified Astronomy Thesaurus concepts: Magnetohydrodynamics (1964); Interplanetary turbulence (830)
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... In plasma turbulence, stable structures may permeate the system and travel undisturbed over long timescales, as one would expect in stellar winds (Borovsky 2008;Pecora et al. 2019) and accretion flows (Ripperda et al. 2020;Nathanail et al. 2022). These patterns, known as "plasmoids" or "magnetic vortices" for their geometrical resemblance to hydrodynamical vortices, might be a crucial element of particle energization and dissipation (Drake et al. 2010;Petropoulou et al. 2016;Khabarova et al. 2021;El Mellah et al. 2022). Despite intense investigations, very little is known about their internal structure (Allanson et al. 2016;Lukin et al. 2018), mostly because of the coupling between large scales and characteristic plasma length scales. ...
... While this 2D approximation differs qualitatively from the (more complex and expensive) 3D case, it may still provide insights into some relaxation processes characteristic of magnetized astrophysical plasmas. Indeed, these equilibria might also be relevant for full 3D anisotropic settings, in cases where an external field effectively reduces the dimensionality of turbulence (Shebalin et al. 1983;Chernoglazov et al. 2021;Khabarova et al. 2021;Ripperda et al. 2022). In such a general case, which will motivate future investigations, the KVR model can acquire a weak dependency along the magnetic field coordinate, say z, as typical of solar flux ropes. ...
Long-lived Equilibria in Kinetic Astrophysical Plasma Turbulence
Article
Full-text available
  • Aug 2024
Turbulence in classical fluids is characterized by persistent structures that emerge from the chaotic landscape. We investigate the analogous process in fully kinetic plasma turbulence by using high-resolution, direct numerical simulations in two spatial dimensions. We observe the formation of long-lived vortices with a profile typical of macroscopic, magnetically dominated force-free states. Inspired by the Harris pinch model for inhomogeneous equilibria, we describe these metastable solutions with a self-consistent kinetic model in a cylindrical coordinate system centered on a representative vortex, starting from an explicit form of the particle velocity distribution function. Such new equilibria can be simplified to a Gold–Hoyle solution of the modified force-free state. Turbulence is mediated by the long-lived structures, accompanied by transients in which such vortices merge and form self-similarly new metastable equilibria. This process can be relevant to the comprehension of various astrophysical phenomena, going from the formation of plasmoids in the vicinity of massive compact objects to the emergence of coherent structures in the heliosphere.
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... During this process, the stored magnetic energy converts into heat, kinetic energy, and radiation. Several theoretical studies have been conducted to understand the activities of small-to large-scale magnetic structures in the solar atmosphere, such as solar flares, jets, spicules, filament eruptions, coronal mass ejection, and space plasma (e.g., Shibata et al. 1995;Yokoyama & Shibata 1995;Shibata 1999;Priest & Forbes 2000;Yamada et al. 2010;Ding et al. 2011;Chen 2011;Shibata & Magara 2011;Hesse & Cassak 2020;Khabarova et al. 2021). However, direct observation of magnetic reconnection in the solar atmosphere remains elusive. ...
Formation of Jet-driven Forced Reconnection Region and Associated Plasma Blobs in a Prominence Segment
Preprint
  • Feb 2025
We use data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the most likely formation of a forced reconnection region and associated plasma blobs, triggered by jet-like structures in a prominence segment. Around 05:44 UT on December 16th^{th}, 2017, hot jet-like structures lifted from a nearby active region and fell obliquely on one side of the prominence segment with velocities of ≈\approx45--65 km s−1^{-1}. These eruptions compressed the boundaries of the prominence and flux rope, forming an elongated reconnection region with inflow velocities of 47--52 km s−1^{-1} and 36--49 km s−1^{-1} in the projected plane. A thin, elongated reconnection region was formed, with multiple magnetic plasma blobs propagating bidirectionally at velocities of 91--178 km s−1^{-1}. These dense blobs, associated with ongoing reconnection, may also be linked to the onset of Kelvin-Helmholtz (K-H) instability. The blobs are attributed to plasmoids, moving at slower speeds (91--178 km s−1^{-1}) due to the high density in the prominence segment. The dimensionless reconnection rate varied from 0.57--0.28, 0.53--0.26, and 0.41--0.20, indicating reconnection rate enhancement and supporting the forced reconnection scenario. After reconnection, the prominence plasma heated to 6 MK, releasing significant thermal energy (≈\approx5.4×\times1027^{27} erg), which drained cool prominence plasma and heated it to coronal temperatures. The ubiquity of jets and outflows in the solar atmosphere makes the aforementioned of reconnection and possible co-existence of K-H instability potentially important for the magnetic energy release and heating in the solar atmosphere.
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... During this process, the stored magnetic energy converts into heat, kinetic energy, and radiation. Several theoretical studies have been conducted to understand the activities of small-to large-scale magnetic structures in the solar atmosphere, such as solar flares, jets, spicules, filament eruptions, coronal mass ejection, and space plasma (e.g., Shibata et al. 1995;Yokoyama & Shibata 1995;Shibata 1999;Priest & Forbes 2000;Yamada et al. 2010;Ding et al. 2011;Chen 2011;Shibata & Magara 2011;Hesse & Cassak 2020;Khabarova et al. 2021). However, direct observation of magnetic reconnection in the solar atmosphere remains elusive. ...
Formation of Jet-driven Forced Reconnection Region and Associated Plasma Blobs in a Prominence Segment
Article
Full-text available
  • Feb 2025
We use data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study 1 the most likely formation of a forced reconnection region and associated plasma blobs, triggered by jet-like structures 2 in a prominence segment. Around 05:44 UT on December 16 th , 2017, hot jet-like structures lifted from a nearby active 3 region and fell obliquely on one side of the prominence segment with velocities of ≈45-65 km s −1. These eruptions 4 compressed the boundaries of the prominence and flux rope, forming an elongated reconnection region with inflow 5 velocities of 47-52 km s −1 and 36-49 km s −1 in the projected plane. A thin, elongated reconnection region was formed, 6 with multiple magnetic plasma blobs propagating bidirectionally at velocities of 91-178 km s −1. These dense blobs, 7 associated with ongoing reconnection, may also be linked to the onset of Kelvin-Helmholtz (K-H) instability. The 8 blobs are attributed to plasmoids, moving at slower speeds (91-178 km s −1) due to the high density in the prominence 9 segment. The dimensionless reconnection rate varied from 0.57-0.28, 0.53-0.26, and 0.41-0.20, indicating reconnection 10 rate enhancement and supporting the forced reconnection scenario. After reconnection, the prominence plasma heated 11 to 6 MK, releasing significant thermal energy (≈5.4×10 27 erg), which drained cool prominence plasma and heated 12 it to coronal temperatures. The ubiquity of jets and outflows in the solar atmosphere makes the aforementioned of 13 reconnection and possible coexistence of K-H instability potentially important for the magnetic energy release and 14 heating in the solar atmosphere. 15
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... The other source of accelerated particles is shocks associated with stream interaction regions representing borders of high-speed flows from coronal holes. There are also mechanisms accelerating particles to MeV energies locally in the solar wind by magnetic reconnection (48). ...
Trends in childhood leukemia incidence in urban countries and their relation to environmental factors, including space weather
Article
Full-text available
  • May 2024
Leukemia is the most common cancer in children. Its incidence has been increasing worldwide since 1910th, suggesting the presence of common sources of the disease, most likely related to people’s lifestyle and environment. Understanding the relationship between childhood leukemia and environmental conditions is critical to preventing the disease. This discussion article examines established potentially-carcinogenic environmental factors, such as vehicle emissions and fires, alongside space weather-related parameters like cosmic rays and the geomagnetic field. To discern the primary contributor, we analyze trends and annual variations in leukemia incidence among 0-14-year-olds in the United States, Canada, Australia, and Russia from 1990 to 2018. Comparisons are drawn with the number of vehicles (representing gasoline emissions) and fire-affected land areas (indicative of fire-related pollutants), with novel data for Russia introduced for the first time. While childhood leukemia incidence is rising in all countries under study, the rate of increase in Russia is twice that of other nations, possibly due to a delayed surge in the country’s vehicle fleet compared to others. This trend in Russia may offer insights into past leukemia levels in the USA, Canada, and Australia. Our findings highlight vehicular emissions as the most substantial environmental hazard for children among the factors examined. We also advocate for the consideration of potential modulation of carcinogenic effects arising from variations in cosmic ray intensity, as well as the protective role of the geomagnetic field. To support the idea, we provide examples of potential space weather effects at both local and global scales. The additional analysis includes statistical data from 49 countries and underscores the significance of the magnetic field dip in the South Atlantic Anomaly in contributing to a peak in childhood leukemia incidence in Peru, Ecuador and Chile. We emphasize the importance of collectively assessing all potentially carcinogenic factors for the successful future predictions of childhood leukemia risk in each country.
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... SMFRs have been observed abundantly in record proximity to the Sun in Parker Solar Probe (PSP) observations (Zhao et al. 2020Chen et al. 2021;Pecora et al. 2021a;Chen & Hu 2022). There is evidence that SMFRs trap, exclude, and accelerate energetic particles (Khabarova & Zank 2017;Zhao et al. 2018;Khabarova et al. 2021;Pecora et al. 2021b;Pezzi et al. 2021;Van Eck et al. 2022;Le Roux 2023). The major open questions regarding SMFRs can be separated as (1) whether SMFRs originate from the Sun or form continuously within the solar wind and (2) whether the SMFRs undergo significant evolution within the solar wind besides the effects of solar wind expansion. ...
Axial Flux Evolution of Small-scale Magnetic Flux Ropes from 0.06 to 10 au
Article
Full-text available
  • Apr 2024
Small-scale magnetic flux ropes (SMFRs) fill much of the solar wind, but their origin and evolution are debated. We apply our recently developed, improved Grad–Shafranov algorithm for the detection and reconstruction of SMFRs to data from Parker Solar Probe, Solar Orbiter, Wind, and Voyager 1 and 2 to detect events from 0.06 to 10 au. We observe that the axial flux density is the same for SMFRs of all sizes at a fixed heliocentric distance but decreases with distance owing to solar wind expansion. Additionally, using the difference in speed between SMFRs, we find that the vast majority of SMFRs will make contact with others at least once during the 100 hr transit to 1 au. Such contact would allow SMFRs to undergo magnetic reconnection, allowing for processes such as merging via the coalescence instability. Furthermore, we observe that the number of SMFRs with higher axial flux increases significantly with distance from the Sun. Axial flux is conserved under solar wind expansion, but the observation can be explained by a model in which SMFRs undergo turbulent evolution by stochastically merging to produce larger SMFRs. This is supported by the observed log-normal axial flux distribution. Lastly, we derive the global number of SMFRs above 10 ¹⁵ Mx near the Sun to investigate whether SMFRs begin their journey as small-scale solar ejections or are continuously generated within the outer corona and solar wind.
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Directional discontinuities in the inner heliosphere from Parker Solar Probe and Solar Orbiter observations
Article
Full-text available
  • Sep 2024
Context. Directional discontinuities (DDs) are common structures in the solar wind plasma and are among the most important discontinuities besides shock waves. The Parker Solar Probe and Solar Orbiter spacecraft currently provide whole new insight into the inner heliosphere in spatial coverage and timescales. Aims. We search for DDs and classify them into subgroups of tangential (TD) and rotational (RD) discontinuities. The analysis of the DD thicknesses allows us to test different theories about their origin and evolution. Methods. We applied an automatic algorithm to select discontinuities between heliocentric distances of 0.06–1.01 AU. The method uses the spatial rotation of the magnetic field to identify the DDs and minimum variance analysis to determine the normal vector of the discontinuity surface. A classification into TDs and RDs was carried out using the magnetic field data and the Walén test in both the spacecraft and the deHoffmann–Teller frame. Results. With strict conditions, we found more than 140 000 DDs in the time intervals. We find that the spatial density of DDs decreases with increasing radial distance from the Sun in the innermost heliosphere. The comprehensive analysis revealed that most of the DD, for which the normal component of the magnetic field is small are in fact TDs, regardless of the jump in field magnitude. After the classification, we were able to determine the radial thickness evolution for the TDs and RDs separately. We found that the thickness of RDs decreases from 0.06 to 0.30 AU, and beyond this (0.30–1.01 AU) it increases with the local ion inertial length. This characteristic scaling is present for TDs throughout between 0.06 and 1.01 AU. Conclusions. Our results give us a simple classification tool for future studies of DDs, that is based only on magnetic field measurements. After we analyzed the DD thickness, we observationally confirmed that RDs are produced by Alfvén-wave steepening, while the TDs are most likely the boundaries of flux tubes.
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Флуктуации электрического и магнитного полей в плазменном слое хвоста магнитосферы земли по данным MMS
Article
  • Jun 2024
Проведен статистический анализ спектров флуктуаций электрического и магнитного поля в плазменном слое хвоста магнитосферы Земли по данным спутников миссии Multiscale Magnetosphere Mission (MMS) за 2017–2022 гг. при небольших скоростях движения плазмы. Рассмотрены результаты измерений комплекса аппаратуры FIELDS. Выделены трехчасовые интервалы, во время которых спутники находились внутри плазменного слоя и плазменный параметр β был больше единицы. Проведен анализ более ста тысяч спектров флуктуаций электрического поля прибором EDP/DCE и магнитного поля прибором FGM. Из рассмотрения были исключены интервалы со скоростями плазмы свыше 100 км/с. Для каждого интервала определены показатели наклонов спектров в частотном диапазоне 0.014–16 Гц. Выявлено, что величины показателей спектров существенно отличаются для электрического и магнитного поля. Получены зависимости показателей спектров от усредненных по интервалу уровней флуктуаций электрического и магнитного полей.
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Turbulence and particle energization in twisted flux ropes under solar-wind conditions
Article
Full-text available
  • Mar 2024
Context. The mechanisms regulating the transport and energization of charged particles in space and astrophysical plasmas are still debated. Plasma turbulence is known to be a powerful particle accelerator. Large-scale structures, including flux ropes and plasmoids, may contribute to confining particles and lead to fast particle energization. These structures may also modify the properties of the turbulent, nonlinear transfer across scales. Aims. We aim to investigate how large-scale flux ropes are perturbed and, simultaneously, how they influence the nonlinear transfer of turbulent energy toward smaller scales. We then intend to address how these structures affect particle transport and energization. Methods. We adopted magnetohydrodynamic simulations perturbing a large-scale flux rope in solar-wind conditions and possibly triggering turbulence. Then, we employed test-particle methods to investigate particle transport and energization in the perturbed flux rope. Results. The large-scale helical flux rope inhibits the turbulent cascade toward smaller scales, especially if the amplitude of the initial perturbations is not large (∼5%). In this case, particle transport is inhibited inside the structure. Fast particle acceleration occurs in association with phases of trapped motion within the large-scale flux rope.
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Unusual enhancement of ~ 30 MeV proton flux in an ICME sheath region
Article
Full-text available
  • Dec 2021
  • EARTH PLANETS SPACE
In gradual Solar Energetic Particle (SEP) events, shock waves driven by coronal mass ejections (CMEs) play a major role in accelerating particles, and the energetic particle flux enhances substantially when the shock front passes by the observer. Such enhancements are historically referred to as Energetic Storm Particle (ESP) events, but it remains unclear why ESP time profiles vary significantly from event to event. In some cases, energetic protons are not even clearly associated with shocks. Here, we report an unusual, short-duration proton event detected on 5 June 2011 in the compressed sheath region bounded by an interplanetary shock and the leading edge of the interplanetary CME (or ICME) that was driving the shock. While < 10 MeV protons were detected already at the shock front, the higher-energy (> 30 MeV) protons were detected about four hours after the shock arrival, apparently correlated with a turbulent magnetic cavity embedded in the ICME sheath region.
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Predictability of the variable solar-terrestrial coupling
Preprint
Full-text available
  • Jan 2021
In October 2017, the Scientific Committee on Solar-Terrestrial Physics (SCOSTEP) Bureau established a committee for the design of SCOSTEP's Next Scientific Program (NSP). The NSP committee members and authors of this paper, decided from the very beginning of their deliberations that the predictability of the Sun-Earth System from a few hours to centuries is a timely scientific topic, combining the interests of different topical communities in a relevant way. Accordingly, the NSP was christened PRESTO – Predictability of the variable Solar-Terrestrial coupling. This paper presents a detailed account of PRESTO; we show the key milestones of the PRESTO roadmap for the next five years, review the current state of the art and discuss future studies required for the most effective development of solar-terrestrial physics.
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The origin of reconnection-mediated transient brightenings in the solar transition region
Article
Full-text available
  • Mar 2021
  • Nat. Astron.
The ultraviolet emission from the solar transition region is dominated by dynamic, low-lying magnetic loops. The enhanced spatial and temporal resolution of the solar observation satellite Interface Region Imaging Spectrograph (IRIS) has made it possible to study these structures in fine detail. IRIS has observed ‘transient brightenings’ in these loops, associated with strong excess line broadenings1,2 providing important clues to the mechanisms that heat the solar atmosphere. However, the physical origin of the brightenings is debated. The line broadenings have been variously interpreted as signatures of nanoflares³, magneto-hydrodynamic turbulence⁴, plasmoid instabilities⁵ and magneto-acoustic shocks⁶. Here we use IRIS slit-jaw images and spectral data, and the Atmospheric Imaging Assembly of the Solar Dynamics Observatory spacecraft, to show that the brightenings are consistent with magnetic-reconnection-mediated impulsive heating at field-line braiding sites in multi-stranded transition-region loops. The spectroscopic observations present evidence for preferential heating of heavy ions from the transition region and we show that this is consistent with ion cyclotron turbulence caused by strong currents at the reconnection sites. Time-dependent differential emission measure distributions are used to determine the heating frequency7–9 and to identify pockets of faintly emitting ‘super-hot’ plasma. The observations we present and the techniques we demonstrate open up a new avenue of diagnostics for reconnection-mediated energy release in solar plasma.
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Investigating 1st and 2nd order Fermi acceleration of energetic particles by small-scale magnetic flux ropes at 1AU
Article
Full-text available
  • Sep 2020
A new telegrapher-type Parker transport equation was derived from the existing underlying focused transport equation to model the acceleration of energetic particles by contracting and reconnecting small-scale magnetic flux ropes (SMFRs) in the large-scale solar wind. Time-dependent and steady-state analytical solutions were found that unify all SMFR acceleration mechanisms present in the transport equation, showing that SMFR acceleration by the parallel reconnection electric field in the mixed spatial and momentum derivative transport term is constrained by and requires the presence of 2nd order Fermi SMFR acceleration. We explore the potential of these solutions in reproducing energetic proton flux enhancements and spectral evolution between ∼50 keV-5 MeV in dynamic SMFR regions near large-scale reconnecting current sheets in the solar wind at 1 AU. It is shown that both 2nd order Fermi SMFR acceleration involving the variance in SMFR compression and incompressible parallel shear flow, and 1st order SMFR Fermi acceleration due to mean SMFR compression are both workable options in reproducing observed flux amplification factors when using reasonable SMFR parameters. However, the predicted substantial quantitative differences in the spatial evolution of the accelerated spectra through the SMFR region might provide a diagnostic to distinguish between 1st and 2nd order Fermi SMFR acceleration in observations.
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Thin Current Sheets of Sub‐ion Scales observed by MAVEN in the Martian Magnetotail
Article
Full-text available
Plain Language Summary We investigate the structure of cross‐tail current sheets (CSs) in the Martian magnetotail. The CSs play a crucial role in the conversion of magnetic energy into kinetic and thermal energy of plasma particles via magnetic reconnection. Signatures of magnetic reconnection were reported in the Martian magnetotail, but the mechanisms leading to reconnection onset are still unknown. Previous observations in the Earth magnetotail showed that the stretching of the CS magnetic configuration leads to formation of thin CS embedded into a thicker one. Such multiscale configuration can be a source of free energy for excitation of ion tearing mode. The development of this mode can generate X‐type and/or O‐type magnetic configuration and trigger reconnection. By using MAVEN spacecraft observations, we reported the formation of multiscale CS structure in the Martian magnetotail with the inner super thin current sheet (STCS) having a half‐thickness much less than proton gyroradius. We showed that the STCS can be in the metastable state. Thus, the CS thinning and the formation of STCS can lead to a new metastable equilibrium, in which the CS undergoes topological changes enabling the process of fast magnetic reconnection.
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The Evolution of Inverted Magnetic Fields Through the Inner Heliosphere
Article
Full-text available
  • May 2020
  • MON NOT R ASTRON SOC
Local inversions are often observed in the heliospheric magnetic field (HMF), but their origins and evolution are not yet fully understood. Parker Solar Probe has recently observed rapid, Alfvénic, HMF inversions in the inner heliosphere, known as ‘switchbacks’, which have been interpreted as the possible remnants of coronal jets. It has also been suggested that inverted HMF may be produced by near-Sun interchange reconnection; a key process in mechanisms proposed for slow solar wind release. These cases suggest that the source of inverted HMF is near the Sun, and it follows that these inversions would gradually decay and straighten as they propagate out through the heliosphere. Alternatively, HMF inversions could form during solar wind transit, through phenomena such velocity shears, draping over ejecta, or waves and turbulence. Such processes are expected to lead to a qualitatively radial evolution of inverted HMF structures. Using Helios measurements spanning 0.3–1 au, we examine the occurrence rate of inverted HMF, as well as other magnetic field morphologies, as a function of radial distance r, and find that it continually increases. This trend may be explained by inverted HMF observed between 0.3 and 1 au being primarily driven by one or more of the above in-transit processes, rather than created at the Sun. We make suggestions as to the relative importance of these different processes based on the evolution of the magnetic field properties associated with inverted HMF. We also explore alternative explanations outside of our suggested driving processes which may lead to the observed trend.
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An Alternative Interpretation of Impulsive SEP Events Occurring on 1999 January 9–10
Article
  • Sep 2020
  • ASTROPHYS J
We have examined two impulsive solar energetic particle events that occurred on 1999 January 9–10 (earlier event A and later event B). Both events showed earlier velocity dispersion and later intensity dropout of ions. In particular, in event A, the dropout repeated five times. Through the onset time analysis of solar particles, we find that only at higher energies (>0.2 MeV nucleon ⁻¹ for heavy ions and >2.8 keV for electrons) can the analysis provide a consistent path length of ions and electrons. The path length in event A is larger than that in event B. In contrast, at lower energies, the analysis fails to predict the distribution of first arrival of solar particles. The divergence between observation and prediction would increase if the interplanetary scattering of ions were taken into account. We then focus on the lower-energy region, where a negative correlation of ion intensities with plasma β is displayed. We have found that the repeated dropout of ions can be caused by the magnetic reconnection acceleration in the solar wind. In addition, we have discovered an isolated proton dropout event in which a sharply anisotropic pitch-angle distribution of low-energy electrons is also seen. Our observation is consistent with the prediction of Tautz et al. that a minimum power spectral density component parallel to the magnetic field can reduce the magnetic mirroring effect, preventing electron scattering through 90°.
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Pitch-angle distribution of accelerated electrons in 3D current sheets with magnetic islands
Article
  • Feb 2021
Aims. This research aims to explore variations of electron pitch-angle distributions (PADs) during spacecraft crossing of reconnecting current sheets (RCSs) with magnetic islands. Our results can benchmark the sampled characteristic features with realistic PADs derived from in situ observations. Methods. Particle motion is simulated in 2.5D Harris-type RCSs using the particle-in-cell method and considering the plasma feedback to electromagnetic fields induced by accelerated particles. We evaluate particle energy gains and PADs in different locations with virtual spacecraft passing the current sheet while moving in the different directions. The RCS parameters are comparable to heliosphere and solar wind conditions. Results. The energy gains and the PADs of particles would change depending on the specific topology of the magnetic fields. In addition, the observed PADs also depend on the crossing paths of the spacecraft. When the guiding field is weak, the bi-directional electron beams (strahls) are mainly present inside the islands and are located just above or below the X-nullpoints in the inflow regions. The magnetic field relaxation near the X-nullpoint alters the PADs towards 90°. As the guiding field becomes larger, the regions with bi-directional strahls are compressed towards small areas in the exhausts of RCSs. Mono-directional strahls are quasi-parallel to the magnetic field lines near the X-nullpoint due to the dominant Fermi-type magnetic curvature-drift acceleration. Meanwhile, the high-energy electrons confined inside magnetic islands create PADs of around 90°. Conclusions. Our results link the electron PADs to local magnetic structures and the directions of spacecraft crossings. This can help to explain a variety of the PAD features reported in recent observations in the solar wind and the Earth’s magnetosphere.
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Identification of coherent structures in space plasmas: The magnetic helicity-PVI method
Article
  • Nov 2020
Context. Plasma turbulence can be viewed as a magnetic landscape populated by large- and small-scale coherent structures. In this complex network, large helical magnetic tubes might be separated by small-scale magnetic reconnection events (current sheets). However, the identification of these magnetic structures in a continuous stream of data has always been a challenging task. Aims. Here, we present a method that is able to characterize both the large- and small-scale structures of the turbulent solar wind, based on the combined use of a filtered magnetic helicity ( H m ) and the partial variance of increments (PVI). Methods. This simple, single-spacecraft technique was first validated via direct numerical simulations of plasma turbulence and then applied to data from the Parker Solar Probe mission. Results. This novel analysis, combining H m and PVI methods, reveals that a large number of flux tubes populate the solar wind and continuously merge in contact regions where magnetic reconnection and particle acceleration may occur.
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Scattering of strahl electrons in the solar wind between 0.3 and 1 au: Helios observations
Article
  • Jul 2019
  • MON NOT R ASTRON SOC
Electron velocity distribution functions in the solar wind according to standard models consist of four components, of which three are symmetric – the core, the halo, and the superhalo, and one is magnetic field-aligned, beam-like population, referred to as the strahl. We analysed in situ measurements provided by the two Helios spacecrafts to study the behaviour of the last, the strahl electron population, in the inner Solar system between 0.3 and 1 au. The strahl is characterized with a pitch-angle width (PAW) depending on electron energy and evolving with radial distance. We find different behaviour of the strahl electrons for solar wind separated into types by the core electron beta parallel value (βec∥). For the low-βec∥ solar wind the strahl component is more pronounced, and the variation of PAW is electron energy dependent. At low energies a slight focusing over distance is observed, and the strahl PAW measured at 0.34 au agrees with the width predicted by a collisionless focusing model. The broadening observed for higher energy strahl electrons during expansion can be described by an exponential relation, which points towards an energy-dependent scattering mechanism. In the high-βec∥ solar wind the strahl appears broader in consistence with the high-βec∥ plasma being more unstable with respect to kinetic instabilities. Finally we extrapolate our observations to the distance of 0.16 au, predicting the strahl PAWs in the low-βec∥ solar wind to be ∼29° for all energies, and in the high-βec∥ solar wind a bit broader, ranging between 37° and 65°.
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