Identifying and Quantifying the Role of Magnetic Reconnection in Space Plasma Turbulence

Author(s):  
Jeffersson Andres Agudelo Rueda ◽  
Daniel Verscharen ◽  
Robert Wicks ◽  
Christopher Owen ◽  
Georgios Nicolaou ◽  
...  

<p>One of the outstanding open questions in space plasma physics is the heating problem in the solar corona and the solar wind. In-situ measurements, as well as MHD and kinetic simulations, suggest a relation between the turbulent nature of plasma and the onset of magnetic reconnection as a channel of energy dissipation, particle acceleration and a heating mechanism. It has also been proven that non-linear interactions between counter propagating Alfvén waves drives plasma towards a turbulent state. On the other hand, the interactions between particles and waves becomes stronger at scales near the ion(electron) gyroradious ρi (ρe ), and so turbulence can enhance conditions for reconnection and increase the number of reconnection sites. Therefore, there is a close link between turbulence and reconnection. We use fully kinetic particle in cell (PIC) simulations, able to resolve the kinetic phenomena, to study the onset of reconnection in a 3D simulation box with parameters similar to the solar wind under Alfvénic turbulence. We identify in our simulations characteristic features of reconnection sites as steep gradients of the magnetic field strength alongside with the formation of strong current sheets and inflow-outflow patterns of plasma particles near the diffusion regions. These results will be used to quantify the role reconnection in plasma turbulence.</p>

2021 ◽  
Author(s):  
Anna Tenerani ◽  
Marco Velli ◽  
Lorenzo Matteini

<p>Alfvénic fluctuations represent the dominant contributions to turbulent fluctuations in the solar wind, especially, but not limited to, the fastest streams with velocity of the order of 600-700 km/s. Alfvénic fluctuations can contribute to solar wind heating and acceleration via wave pressure and turbulent heating. Observations show that such fluctuations are characterized by a nearly constant magnetic field amplitude, a condition which remains largely to be understood and that may be an indication of how fluctuations evolve and relax in the expanding solar wind. Interestingly, measurements from Parker Solar Probe have shown the ubiquitous and persistent presence of the so-called switchbacks. These are magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field. The corresponding signature of switchbacks in the velocity field is that of local enhancements in the radial speed (or jets) that display the typical velocity-magnetic field correlation that characterizes Alfvén waves propagating away from the Sun. While there is not yet a general consensus on what is the origin of switchbacks and their connection to coronal activity, a first necessary step to answer these important questions is to understand how they evolve and how long they can persist in the solar wind. Here we investigate the evolution of switchbacks. We address how their evolution is affected by parametric instabilities and the possible role of expansion, by comparing models with the observed radial evolution of the fluctuations’ amplitude. We finally discuss what are the implications of our results for models of switchback generation and related open questions.</p>


2011 ◽  
Vol 172 (1-4) ◽  
pp. 325-342 ◽  
Author(s):  
T. S. Horbury ◽  
R. T. Wicks ◽  
C. H. K. Chen

Author(s):  
Dudok Kh.R.

The article analyzes the role of phraseological constituents in the process of replenishment in the mobile communication terminology. It is noted that phraseological units carry much more information than a single word and should be studied and taken into account in various aspects: cognitive, linguistic and cultural, functional, etc. It is argued that cognitive phraseological units as constituents of the language system are used by native speakers to describe semantic processes and states. It is proved that the deep semantic nature of phraseology has been emerged under the influence of socio-domestic, political and other social phenomena. Some constituents in the professional language through time acquire additional, situational meaning, i.e. new semantic content of constant expressions giving it a special text format. It is suggested that the semantic structure of the phraseological component in professional speech is formed by a set of its semantic elements, which are closely correlated with each other. It is stressed that the components of phraseological semantics, in turn, are divided into semantic components, semantic features that act not only as constituents of the main semantic components of phraseology, but also as a close link between them. Thus, such characteristic features of phraseological constituents as internal form, motivation, imagery, idiomaticity and stability, enable the phraseological units to create semantic transformation. It is argued that the professional language of mobile communication is filled with phraseological constituents, in which the value of the whole combination is not accurate, and sometimes not deduced from the sum of its components, or dominates the value of its components. It is concluded that phraseology is one of the inexhaustible sources of richness and expressiveness of speech, which nourishes the professional subtext of mobile communication, gives it an artistic sounding, filled with components of lexical and syntactic sophistication and completeness. We may sum up that the phraseological constituent is a productive semantic and stylistic means, so metaphor and metonymy are used in various spheres of language, the terminology of mobile communication in particular.Key words: phraseological constituents, internal form, meanings, sences, concept, idiomaticity, metaphor, metonymy. У статті проаналізовано роль фразеологічних конституентів у процесі поповнення терміносистеми мобільний зв’язок. Зазначено, що фразеологізми мають набагато більше інформації в порівнянні з окремим словом та їх слід вивчати й враховувати в різних аспектах: когнітивному, лінгвокультурологічному, функціональному тощо. Стверджується, що когнітивно фразеологічні одиниці як конституенти мовної системи використовуються носіями мови для опису смислових процесів і станів. Доведено, що глибинна семантична природа фразеологізмів полягає в тому, що під впливом соціально-побутових, політичних та інших суспільних явищ деякі конституанти у фаховій мові із часом набувають додаткового, ситуативного смислу, тобто нового смислового наповнення сталим висловам надає спеціальний текстовий форматив. Висунуто припущення, що семан-тичну структуру фразеологічного компонента у фаховому мовленні формує сукупність його семантичних елементів, що знаходяться між собою в тісних кореляціях. Розвинуто думку, що складові частини фразеологічної семантики своєю чергою розчленовуються на семантичні компоненти, семантичні ознаки, що виступають не тільки як конституенти основних семантичних складових частин фразеологізму, але і як тісна сполучна ланка між ними. Таким чином, такі характерні риси фразеологічних конституентів, як внутрішня форма, мотивованість, образність, ідіоматичність і стійкість уможливлюють здатність фразеологізмів до семантичної трансформації. Аргументовано, що фахова мова мобільного зв’язку наповнена фразеологічними конституентами, в яких значення цілого сполучення не точне, а іноді й зовсім не виводиться із суми складових компонентів або домінує над значенням складових частин. Зроблено висновок, що фразеологізми є одним із невичерпних джерел багатства й виразності мовлення, які живлять фахову підмову мобільного зв’язку, надають їй художнього зву-чання, наповнюють компонентами лексичної та синтаксичної витонченості й завершеності. Підсумовано, що фразеологічний конституент є продуктивним семантико-стилістичним засобом, так само як і метафора, метонімія, які використовується в різних сферах мови, зокрема терміносистеми мобільного зв’язку.Ключові слова:фразеологічні значення, внутрішня форма, значення, смисли, концепт, ідіоматичність, метафора, метонімія.


2021 ◽  
Author(s):  
Patricio A. Munoz ◽  
Jörg Büchner ◽  
Neeraj Jain

<p>Turbulence is ubiquitous in solar system plasmas like those of the solar wind and Earth's magnetosheath. Current sheets can be formed out of this turbulence, and eventually magnetic reconnection can take place in them, a process that converts magnetic into particle kinetic energy. This interplay between turbulence and current sheet formation has been extensively analyzed with MHD and hybrid-kinetic models. Those models cover all the range between large Alfvénic scales down to ion-kinetic scales. The consequences of current sheet formation in plasma turbulence that includes electron dynamics has, however, received comparatively less attention. For this sake we carry out 2.5D fully kinetic Particle-in-Cell simulations of kinetic plasma turbulence including both ion and electron spectral ranges. In order to further assess the electron kinetic effects, we also compare our results with hybrid-kinetic simulations including electron inertia in the generalized Ohm's law. We analyze and discuss the electron and ion energization processes in the current sheets and magnetic islands formed in the turbulence. We focus on the electron and ion distribution functions formed in and around those current sheets and their stability properties that are relevant for the micro-instabilities feeding back into the turbulence cascade. We also compare pitch angle distributions and non-Maxwellian features such as heat fluxes with recent in-situ solar wind observations, which demonstrated local particle acceleration processes in reconnecting solar wind current sheets [Khabarova et al., ApJ, 2020].</p>


2021 ◽  
Author(s):  
Jeffersson Andres Agudelo Rueda ◽  
Daniel Verscharen ◽  
Robert T Wicks ◽  
Christopher J Owen ◽  
Georgios Nicolaou ◽  
...  

<p>Heating and energy dissipation in the solar wind remain important open questions. Turbulence and reconnection are two candidate processes to account for the energy transport to subproton scales at which, in collisionless plasmas, the energy ultimately dissipates. Understanding the effects of small-scale reconnection events in the energy cascade requires the identification of these events in observational data as well as in 3D simulations. We use an explicit fully kinetic particle-in-cell code to simulate 3D small scale magnetic reconnection events forming in anisotropic and Alfvénic decaying turbulence. We define a set of indicators to find reconnection sites in our simulation based on intensity thresholds.  According to the application of these indicators, we identify the occurrence of reconnection events in the simulation domain and analyse one of these events in detail. The event is highly dynamic and asymmetric. We study the profiles of plasma and magnetic-field fluctuations recorded along artificial-spacecraft trajectories passing near and through the reconnection region as well as the energy exchange between particles and fields during this event. Our results suggest the presence of particle heating and acceleration related to asymmetric small-scale reconnection of magnetic flux tubes produced by the anisotropic Alfvénic turbulent cascade in the solar wind. These events are related to current structures of order a few ion inertial lengths in size.</p>


2020 ◽  
Author(s):  
Jan Deca

<p>All lunar swirls are known to be co-located with crustal magnetic anomalies (LMAs). Not all LMAs can be associated with albedo markings, making swirls, and their possible connection with the former, an intriguing puzzle yet to be solved.</p><p>Given favorable conditions, an LMA can deflect the solar wind enough to form a mini-magnetosphere that partially (and possibly only temporarily) shields the underlying lunar regolith. Recent modeling efforts have shown that the resulting energy flux pattern to the surface is consistent with the underlying albedo (swirl) patterns. In particular, coupling a fully kinetic particle-in-cell code with a downward-continued magnetic field model based on orbital-altitude observations, we are able to produce a pattern similar to Reiner Gamma’s alternating bright and dark bands, but only when integrating over the full lunar orbit. Although consistent with the solar-wind standoff hypothesis for the origin of swirls, the match is not perfect. A combination of reasons could be the cause.</p><p>Here we discuss some of the unexplained discrepancies between the flux profile and the surface brightness and why the Reiner Gamma swirl region should be a prime target for future low-orbiting spacecraft or even landers/rovers, and we consider the potential role of human exploration.</p>


2010 ◽  
Vol 28 (5) ◽  
pp. 1075-1100 ◽  
Author(s):  
U. Taubenschuss ◽  
N. V. Erkaev ◽  
H. K. Biernat ◽  
C. J. Farrugia ◽  
C. Möstl ◽  
...  

Abstract. We investigate the propagation of magnetic clouds (MCs) through the inner heliosphere using 2.5-D ideal magnetohydrodynamic (MHD) simulations. A numerical solution is obtained on a spherical grid, either in a meridional plane or in an equatorial plane, by using a Roe-type approximate Riemann solver in the frame of a finite volume approach. The structured background solar wind is simulated for a solar activity minimum phase. In the frame of MC propagation, special emphasis is placed on the role of the initial magnetic handedness of the MC's force-free magnetic field because this parameter strongly influences the efficiency of magnetic reconnection between the MC's magnetic field and the interplanetary magnetic field. Magnetic clouds with an axis oriented perpendicular to the equatorial plane develop into an elliptic shape, and the ellipse drifts into azimuthal direction. A new feature seen in our simulations is an additional tilt of the ellipse with respect to the direction of propagation as a direct consequence of magnetic reconnection. During propagation in a meridional plane, the initial circular cross section develops a concave-outward shape. Depending on the initial handedness, the cloud's magnetic field may reconnect along its backside flanks to the ambient interplanetary magnetic field (IMF), thereby losing magnetic flux to the IMF. Such a process in combination with a structured ambient solar wind has never been analyzed in detail before. Furthermore, we address the topics of force-free magnetic field conservation and the development of equatorward flows ahead of a concave-outward shaped MC. Detailed profiles are presented for the radial evolution of magnetoplasma and geometrical parameters. The principal features seen in our MHD simulations are in good agreement with in-situ measurements performed by spacecraft. The 2.5-D studies presented here may serve as a basis under more simple geometrical conditions to understand more complicated effects seen in 3-D simulations.


2014 ◽  
Vol 21 (6) ◽  
pp. 1075-1083 ◽  
Author(s):  
H. Comişel ◽  
Y. Narita ◽  
U. Motschmann

Abstract. Wavevector anisotropy of ion-scale plasma turbulence is studied at various values of ion beta. Two complementary methods are used. One is multi-point measurements of magnetic field in the near-Earth solar wind as provided by the Cluster spacecraft mission, and the other is hybrid numerical simulation of two-dimensional plasma turbulence. Both methods demonstrate that the wavevector anisotropy is reduced with increasing values of ion beta. Furthermore, the numerical simulation study shows the existence of a scaling law between ion beta and the wavevector anisotropy of the fluctuating magnetic field that is controlled by the thermal or hybrid particle-in-cell simulation noise. Likewise, there is weak evidence that the power-law scaling can be extended to the turbulent fluctuating cascade. This fact can be used to construct a diagnostic tool to determine or to constrain ion beta using multi-point magnetic field measurements in space.


2015 ◽  
Vol 33 (4) ◽  
pp. 457-470 ◽  
Author(s):  
V. Zharkova ◽  
O. Khabarova

Abstract. Particles of fast solar wind in the vicinity of the heliospheric current sheet (HCS) or in a front of interplanetary coronal mass ejections (ICMEs) often reveal very peculiar energy or velocity profiles, density distributions with double or triple peaks, and well-defined streams of electrons occurring around or far away from these events. In order to interpret the parameters of energetic particles (both ions and electrons) measured by the WIND spacecraft during the HCS crossings, a comparison of the data was carried out with 3-D particle-in-cell (PIC) simulations for the relevant magnetic topology (Zharkova and Khabarova, 2012). The simulations showed that all the observed particle-energy distributions, densities, ion peak velocities, electron pitch angles and directivities can be fitted with the same model if the heliospheric current sheet is in a status of continuous magnetic reconnection. In this paper we present further observations of the solar-wind particles being accelerated to rather higher energies while passing through the HCS and the evidence that this acceleration happens well before the appearance of the corotating interacting region (CIR), which passes through the spacecraft position hours later. We show that the measured particle characteristics (ion velocity, electron pitch angles and the distance at which electrons are turned from the HCS) are in agreement with the simulations of additional particle acceleration in a reconnecting HCS with a strong guiding field as measured by WIND. A few examples are also presented showing additional acceleration of solar-wind particles during their passage through current sheets formed in a front of ICMEs. This additional acceleration at the ICME current sheets can explain the anticorrelation of ion and electron fluxes frequently observed around the ICME's leading front. Furthermore, it may provide a plausible explanation of the appearance of bidirectional "strahls" (field-aligned most energetic suprathermal electrons) at the leading edge of ICMEs as energetic electrons generated during a magnetic reconnection at the ICME-front current sheet.


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