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Currents in the solar atmosphere and a theory of solar flares

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... The momentum conservation enables this two-fluid model to describe a very low-frequency two-stream instability, which, contrary to conventional presumptions, maintains its characteristic behavior even if the plasma is extremely collisional. This lowfrequency two-stream instability will be referred to as an evacuation instability because it has similarities to an evacuation mechanism proposed long ago by Alfv en and Carlqvist 20 and then elaborated by Carlqvist 21 in the context of density depletion and double-layer formation with the important exceptions that here (i) collisionality is taken into account and (ii) the driver of the evacuation instability is a naturally occurring periodic constriction of the plasma cross section. ...
... The collision terms in Eqs. (18) and (19) can be arbitrarily large without affecting Eq. (20). If the collision effects are neglected and the cross-sectional area A is assumed to be uniform, the system of Eqs. ...
... If the collision effects are neglected and the cross-sectional area A is assumed to be uniform, the system of Eqs. (16)- (20) reduces to Carlqvist's collisionless evacuation mechanism 21 and to the collisionless equations studied by Galeev et al. 35 and by Bulanov and Sasorov. 36 Because collision effects and a constricted A are not considered in Refs. ...
Article
The two-stream instability (Buneman instability) is traditionally derived as a collisionless instability with the presumption that collisions inhibit this instability. We show here via a combination of a collisional two-fluid model and associated experimental observations made in the Caltech plasma jet experiment, that in fact, a low-frequency mode of the two-stream instability is indifferent to collisions. Despite the collision frequency greatly exceeding the growth rate of the instability, the instability can still cause an exponential growth of electron velocity and a rapid depletion of particle density. Nevertheless, high collisionality has an important effect as it enables the development of a double layer when the cross section of the plasma jet is constricted by a kink-instigated Rayleigh–Taylor instability.
... The collision terms in Eqs. (18) and (19) can be arbitrarily large without affecting Eq. (20). ...
... Contrarily, the derivation of the evacuation instability shows that the existence of the instability, i.e., its threshold and growth rate, is indifferent to collisions since the momentum lost by electrons as a result of collisions equals the momentum gained by ions as demonstrated here in adding Eqs. (18) and (19) to obtain Eq. (20). ...
... However, γ a is assumed to be much smaller than k z c s in the calculation that leads to Eq. (42). In other words, equation (42) is 20 This is the author's peer reviewed, accepted manuscript. However, the online version of record will be different from this version once it has been copyedited and typeset. ...
Preprint
The two-stream instability (Buneman instability) is traditionally derived as a collisionless instability with the presumption that collisions inhibit this instability. We show here via a combination of a collisional two-fluid model and associated experimental observations made in the Caltech plasma jet experiment, that in fact, a low frequency mode of the two-stream instability is indifferent to collisions. Despite the collision frequency greatly exceeding the growth rate of the instability, the instability can still cause an exponential growth of electron velocity and a rapid depletion of particle density. High collisionality nevertheless has an important effect as it enables the development of a double layer when the cross-section of the plasma jet is constricted by a kink-instigated Rayleigh-Taylor instability.
... Despite a tremendous effort in understanding the physics of flares, revealing a comprehensive generic model of a flare, consistent with observations remains one of the longest-standing and impactful questions for space weather research. In particular, the so-called standard model of a solar flare (Shibata & Magara 2011), based on a magnetohydrodynamic (MHD) description of the processes of current-sheet development, magnetic field restructuring, and subsequent acceleration of charged particles, captures well the global picture of a flare, but struggles with explaining more specific questions such as what triggers the flare, how the released energy is split between different channels (including manifestations in specific electromagnetic bands), what determines the characteristic timescales, etc. Considering the inductive property of solar atmospheric plasma configurations (i.e. the induction of the magnetic field by electric current systems and vice versa) as a fundamental storage of free magnetic energy, Alfvén & Carlqvist (1967) proposed a flare model based on the analogy with a closed electric circuit. In this model, the disrup-tion of the electric current leads to the explosive release of the whole magnetic energy of the circuit via local Ohmic heating (cf. ...
... It is expected that these mechanisms could be divided into three main groups: the modulation of the emitting plasma by MHD oscillations, repetitive magnetic reconnection which is periodically induced by an MHD oscillation, and spontaneous repetitive reconnection (see McLaughlin et al. 2018, for a comprehensive review). Taking the effective inductance (L), capacitance (C), and resistance (R) of coronal plasma configurations into account in the Alfvén's flare model (Alfvén & Carlqvist 1967), oscillatory variations of the electric current in the flare loop (considered as an equivalent LCR-contour) were theoretically predicted as a unique feature of the model, naturally leading to QPP (Zaitsev et al. 1998;Khodachenko et al. 2009;Zimovets et al. 2021). In general, the identification of the mechanism for a QPP requires simultaneous observations at different wavelengths which are associated with thermal and nonthermal emission, i.e., in different spectral bands, providing the crucial information about the release and transport of the flare energy through different layers of the solar atmosphere (Zimovets et al. 2021). ...
... Another possible interpretation of the observed QPP is provided by the equivalent LCR-contour model (Zaitsev et al. 1998;Zaitsev & Stepanov 2008;Khodachenko et al. 2009). In this model, the flaring active region is considered as a closed electric circuit (Alfvén & Carlqvist 1967). In the fully-ionised coronal part, the electric current is guided by the loop-like magnetic field. ...
Article
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We present the first multiwavelength simultaneous detection of quasi-periodic pulsations (QPPs) in a superflare (more than a thousand times stronger than known solar flares) on a cool star, in soft X-rays (SXRs, with XMM-Newton) and white light (WL, with Kepler). It allowed for the first ever analysis of oscillatory processes in a stellar flare simultaneously in thermal and nonthermal emissions, conventionally considered to come from the corona and chromosphere of the star, respectively. The observed QPPs have periods 1.5 ± 0.15 hr (SXR) and 3 ± 0.6 hr (WL), and correlate well with each other. The unique relationship between the observed parameters of QPPs in SXR and WL allowed us to link them with oscillations of the electric current in the flare loop, which directly affect the dynamics of nonthermal electrons and indirectly (via ohmic heating) the thermal plasma. These findings could be considered in favor of the equivalent LCR contour model of a flare loop, at least in the extreme conditions of a stellar superflare.
... Despite a tremendous effort in understanding the physics of flares, revealing a comprehensive generic model of a flare, consistent with observations remains one of the longest-standing and impactful questions for space weather research. In particular, the so-called standard model of a solar flare (Shibata & Magara 2011), based on a magnetohydrodynamic (MHD) description of the processes of current-sheet development, magnetic field restructuring, and subsequent acceleration of charged particles, captures well the global picture of a flare, but struggles with explaining more specific questions such as what triggers the flare, how the released energy is split between different channels (including manifestations in specific electromagnetic bands), what determines the characteristic timescales, etc. Considering the inductive property of solar atmospheric plasma configurations (i.e. the induction of the magnetic field by electric current systems and vice versa) as a fundamental storage of free magnetic energy, Alfvén & Carlqvist (1967) proposed a flare model based on the analogy with a closed electric circuit. In this model, the disrup-tion of the electric current leads to the explosive release of the whole magnetic energy of the circuit via local Ohmic heating (cf. ...
... It is expected that these mechanisms could be divided into three main groups: the modulation of the emitting plasma by MHD oscillations, repetitive magnetic reconnection which is periodically induced by an MHD oscillation, and spontaneous repetitive reconnection (see McLaughlin et al. 2018, for a comprehensive review). Taking the effective inductance (L), capacitance (C), and resistance (R) of coronal plasma configurations into account in the Alfvén's flare model (Alfvén & Carlqvist 1967), oscillatory variations of the electric current in the flare loop (considered as an equivalent LCR-contour) were theoretically predicted as a unique feature of the model, naturally leading to QPP (Zaitsev et al. 1998;Khodachenko et al. 2009;Zimovets et al. 2021). In general, the identification of the mechanism for a QPP requires simultaneous observations at different wavelengths which are associated with thermal and nonthermal emission, i.e., in different spectral bands, providing the crucial information about the release and transport of the flare energy through different layers of the solar atmosphere (Zimovets et al. 2021). ...
... Another possible interpretation of the observed QPP is provided by the equivalent LCR-contour model (Zaitsev et al. 1998;Zaitsev & Stepanov 2008;Khodachenko et al. 2009). In this model, the flaring active region is considered as a closed electric circuit (Alfvén & Carlqvist 1967). In the fully-ionised coronal part, the electric current is guided by the loop-like magnetic field. ...
Preprint
Full-text available
We present the first multi-wavelength simultaneous detection of QPP in a superflare (more than a thousand times stronger than known solar flares) on a cool star, in soft X-rays (SXR, with XMM-Newton) and white light (WL, with Kepler). It allowed for the first-ever analysis of oscillatory processes in a stellar flare simultaneously in thermal and non-thermal emissions, conventionally considered to come from the corona and chromosphere of the star, respectively. The observed QPP have periods 1.5±0.151.5 \pm 0.15 hours (SXR) and 3±0.63 \pm 0.6 hours (WL), and correlate well with each other. The unique relationship between the observed parameters of QPP in SXR and WL allowed us to link them with oscillations of the electric current in the flare loop, which directly affect the dynamics of non-thermal electrons and indirectly (via Ohmic heating) the thermal plasma. These findings could be considered in favour of the equivalent LCR-contour model of a flare loop, at least in the extreme conditions of a stellar superflare.
... Впервые идея представить токонесущую петлю как аналог замкнутого электрического контура с замыканием токов под фотосферой была сформулирована в 1967 году (Alfven, Carlqvist, 1967). Концепция базировалась на первых измерениях вертикальных электрических токов в фотосфере, выполненных А.Б. ...
... Также из рис. 2 следует отсутствие резких изменений величины распределенного тока во время вспышек. В то же время многие модели предполагают непосредственное участие электрических токов и токовых слоев во вспышечном процессе (Alfven, Carlqvist, 1967;Parker, 1973;Sokolov, Kosovichev, 1978;Heyvaerts et al., 1977;Priest, Forbes, 2002;Sui, Holman, 2003;Li et al., 2018). Это несоответствие может быть объяснено высокой индуктивностью токопроводящей петли (Alfven, Carlqvist, 1967;Khodachenko et al., 2003) и, следовательно, медленным откликом системы крупномасштабных электрических токов на события в верхних слоях солнечной атмосферы. ...
... В то же время многие модели предполагают непосредственное участие электрических токов и токовых слоев во вспышечном процессе (Alfven, Carlqvist, 1967;Parker, 1973;Sokolov, Kosovichev, 1978;Heyvaerts et al., 1977;Priest, Forbes, 2002;Sui, Holman, 2003;Li et al., 2018). Это несоответствие может быть объяснено высокой индуктивностью токопроводящей петли (Alfven, Carlqvist, 1967;Khodachenko et al., 2003) и, следовательно, медленным откликом системы крупномасштабных электрических токов на события в верхних слоях солнечной атмосферы. 00:00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 ...
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Используя магнитограммы компонент вектора магнитного поля на уровне фотосферы, получаемые инструментом Helioseismic and Magnetic Imager (HMI), установленным на борту космического аппарата Solar Dynamics Observatory (SDO), вычислены вертикальные электрические токи для активной области NOAA 12192 за период с 22 по 25 октября 2014 года с временным разрешением 12 минут. Выявлено наличие в исследуемой активной области (АО) крупномасштабной токовой структуры – распределенного электрического тока, имеющего абсолютные значения в диапазоне (40–90)·1012 А. Предполагается, что распределенный ток охватывает всю АО, и, выходя в верхние слои солнечной атмосферы в одной части области, замыкается через хромосферу и корону на оставшейся ее части. Для проверки этого предположения проанализирована связь временных изменений величины распределенного тока с уровнем корональной активности, а также с интенсивностью ультрафиолетового излучения (УФ) АО в диапазонах длин волн 1600 Å, 304 Å, 193 Å и 94 Å. Показано, что: 1) Временные интервалы максимумов величины распределенного тока совпадают по времени с повышенной вспышечной активностью АО. Отсутствие резких изменений величины распределенного тока во время вспышек может быть объяснено высокой индуктивностью токонесущих петель. 2) Грубая оценка магнитной энергии, выносимой распределенным током в корону, дает для АО NOAA 12192 значения 1033–1034 эрг. Только небольшой объем этой энергии реализуется во время вспышечных процессов в АО, большая ее часть тратится на иные диссипативные процессы в короне. 3) Сравнение временных вариаций интенсивности излучения в канале 193 Å с динамикой распределенного тока в АО показывает хорошую взаимосвязь этих величин (коэффициент корреляции k = 0.63). В то же время отсутствует корреляции между величиной распределенного тока и интенсивностью УФ-излучения в диапазонах 1600 Å, 304 Å и 94 Å. 4) Полученные нами результаты, возможно, могут объясняться концепцией LRC-контура токонесущей корональной петли, предложенной в 1967 году Альфвеном и Карлквистом и развитой в работах В.В. Зайцева, А.В. Степанова и др. Согласно данной модели, крупномасштабные электрические токи должны существовать в верхних слоях солнечной атмосферы и принимать участие в нагреве коронального вещества.
... The power is typically 3-5 × 10 18 erg/s, so that the accumulated energy W during the growth phase (about 1 h) becomes about 5 × 10 22 ergs (or 5 × 10 15 J); note that W = (1/2)I 2 H = 5 × 10 22 ergs for the about L = 100 H, I = 10 7 A (cf. Alfven, 1981). ...
... This loop UL current can unload its magnetic energy when it is disrupted; a loop current system as the source of flare energy was suggested by Alfven (1950Alfven ( , 1981. Chen and Krall (2003) estimated the current intensity to be 10 11 A in launching a prominence to become a coronal mass ejection (CME). ...
... In terms of the current line approach, one of the important future problems is instabilities of the current loop. (Alfven and Carlqvist, 1967) and Alfven (1981) suggested that the formation of the double layer is related to the process of the loop current disruption; the presence of the double layer is confirmed in the process of auroral electron acceleration (Karlsson, 2012). ...
Article
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Auroral substorms and solar flares are basically various manifestations of electromagnetic energy dissipation processes, so it is useful to consider both phenomena in terms of a chain of processes, consisting of power supply (dynamo), transmission (currents/circuits), and dissipation (auroral substorms, solar flares), the electric current approach. In this short review, we briefly describe both phenomena together on the basis of the chain process. It is shown that the introduction of a dynamo process in this consideration provides a step-by-step way of studying both phenomena. It is shown that (a) both the solar wind–magnetosphere dynamo and a photospheric dynamo proposed by Lee et al. (1995) have enough power to accumulate enough energy for the explosive features of both phenomena, respectively. (b) For substorms, the power is accumulated in the inner magnetosphere and inflates it, and for flares, the power is likely to be accumulated in a loop current along and above two-ribbon flares. (c) For substorms, the energy release (unloading) process deflates the inner magnetosphere, resulting in an earthward electric field, and for flares, the disruption of the loop current suggested by Alfven (1950) may be responsible for the energy release.
... For illustrative purposes, when discussing semi-quantitative aspects of the impulsive phase of a flare, the following numbers are chosen, reflecting a moderately large flare: total energy 10 24 J, power 10 21 W and rate of precipitation N = 10 36 s −1 of electrons with energy ε = 10 keV ≈ 10 −15 J. The current, which has long been known from vector magnetograms [Alfvén and Carlqvist, 1967], is taken to be I = 10 11 A, and the EMF to be Φ = 10 10 V, such that the power is IΦ = ε N. ...
... The sudden turning on of a resistance in the corona was referred to as "current interruption" by Alfvén and Carlqvist [1967], who assumed the resistance to be due to a double layer. However, the sudden turning on of a region of enhanced resistance, R c , in a currentcarrying coronal loop causes the current to be partly redirected around the the resistive region [Melrose, 1995;Parker, 1996]. ...
Preprint
Roles played by the currents in the impulsive phase of a solar flare and in a coronal mass ejection (CME) are reviewed. Solar flares are magnetic explosions: magnetic energy stored in unneutralized currents in coronal loops is released into energetic electrons in the impulsive phase and into mass motion in a CME. The energy release is due to a change in current configuration effectively reducing the net current path. A flare is driven by the electromotive force (EMF) due to the changing magnetic flux. The EMF drives a flare-associated current whose cross-field closure is achieved by redirection along field lines to the chromosphere and back. The essential roles that currents play are obscured in the "standard" model and are described incorrectly in circuit models. A semi-quantitative treatment of the energy and the EMF is provided by a multi-current model, in which the currents are constant and the change in the current paths is described by time-dependent inductances. There is no self-consistent model that includes the intrinsic time dependence, the EMF, the flare-associated current and the internal energy transport during a flare. The current, through magnetic helicity, plays an important role in a CME, with twist converted into writhe allowing the kink instability plus reconnection to lead to a new closed loop, and with the current-current force accelerating the CME through the torus instability.
... He labelled the basic unit of impulsive energy release a 'nanoflare' and proposed that large X-ray-producing solar flares are swarms of nanoflares, each of which is too small to be resolved by existing observational methods. On the other hand, Alfvén and Carlqvist 10 and Carlqvist 11 proposed a related but somewhat different model, wherein a double layer forms in a solar magnetic flux tube when the electric current density becomes very large and exceeds some threshold. The electric field associated with the double layer would accelerate particles to high energy. ...
... This can be explained by two associated effects: (1) the development of a kinetic instability when the electron drift velocity v d = J axial /ne, where J axial is the axial current density, n is the electron density and e is the electron charge, associated with electric current exceeds a characteristic wave velocity, such as Alfvén velocity, and (2) a geometric stretching effect. When the electron drift velocity exceeds a threshold, waves are destabilized and increase the local effective electrical resistivity 10,21 . The fastest-growing ideal MHD instabilities are incompressible 18 , which means that the volume of the kinking loop segment must remain constant during the kinking. ...
Article
Full-text available
Solar flares are intense bursts of electromagnetic radiation accompanied by energetic particles and hard X-rays. They occur when magnetic flux loops erupt in the solar atmosphere. Solar observations detect energetic particles and hard X-rays but cannot reveal the generating mechanism because the particle acceleration happens at a scale smaller than the observation resolution. Thus, details of the cross-scale physics that explain the generation of energetic particles and hard X-rays remain a mystery. Here, we present observations from a laboratory experiment that simulates solar coronal loop physics. Transient, localized 7.6-keV X-ray bursts and a several-kilovolt voltage spike are observed in braided magnetic flux ropes of a 2-eV plasma when the braid strand radius is choked down to be at the kinetic scale by either magnetohydrodynamic (MHD) kink or magnetic Rayleigh–Taylor instabilities. This sequence of observations reveals a cross-scale coupling from MHD to non-MHD physics that is likely responsible for generating solar energetic particles and X-ray bursts. All the essential components of this mechanism have been separately observed in the solar corona.
... The space plasma witnesses DLs with a potential drop of about 10 9 -10 11 V [55]. For instance, in the solar atmosphere, DLs are generated by thin current filaments that penetrate it (solar atmosphere) [55], [58]. Nonrelativistic DLs have been theorized by Langmuir [59] and Block [60]. ...
... Chen et al. [64] describe the first direct measurement of how energy from electro-magnetic waves in space is transferred to particles. The studies of Alfvn and Carlqvist [58] on the nature and formation of double-layer is highly informative. According to him, DLs are self-protecting entities in space plasma that encompass intense electric fields between them. ...
Article
Solar radiation, along with cosmic radiation, ionizes the Earth's atmosphere and creates a dense layer known as the ionosphere. By considering weakly relativistic degenerate plasma in the planetary ionosphere, we have studied the formation and nature of the solitary structure, electrostatic double layers (DLs), and so on. As we have considered weak relativistic degeneracy, only electrons get accelerated and are the key to stationary structures. We have implemented Sagdeev's pseudopotential method, standard Gardner equation, and accordingly identified regimes where the solitary formation and DLs may be observed. We have studied the parametric influences on solitons and DLs. Furthermore, we extended our investigation to the oscillatory Rossby solitons in the ionospheric plasma. The results may help interpret many high-energy atmospheric observations in the ionospheric plasma.
... Controversy has existed regarding whether the electric current and magnetic forces are important. A point of view that the electric current and resulting magnetic forces are neither fundamental nor important has been advocated by Parker (1996Parker ( , 2001Parker ( , 2007 who asserted that the magnetic field rather than the electric current is fundamental and objected to the electric current point of view invoked here and previously by Alfvén and Carlqvist (1967), Alfvén (1986), andMelrose (1995). In the author's opinion this dispute is analogous to arguing in mechanics whether acceleration or velocity is the more fundamental quantity, that is, the "prime mover"; arguing that magnetic field is the prime mover is like arguing that velocity is the prime mover driving acceleration. ...
... This setting to 0 of the electron inertia is consistent with treatments of ideal perfect conductors and fails to take into account physics taking place on the length scale of the electron skin depth d e ¼ c/ω pe and on the timescale of the electron plasma and cyclotron frequencies ω pe , ω ce . This model of a large inductive voltage drop leading to oppositely directed ion and electron accelerations is closely related to the double layer concept proposed by Alfvén (1986) to describe the explosive inductive mechanism described by Alfvén and Carlqvist (1967) and by Jacobsen and Carlqvist (1964). The mechanism is explosive because all inductive energy of an initially zero resistance system is dissipated at the localized small segment of an inductive circuit where the electrical resistance becomes finite for some reason. ...
Article
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A comprehensive overview of two decades of Caltech experiments relevant to solar corona physics is presented. The extent to which the experiments scale to the solar corona, the basic configurations and operation, and the importance of the magnetic force J × B common to all the experiments is discussed. Summaries are given of the various configurations used, the main observations, and interpretations of these observations, including new models developed to provide these interpretations. Topics include observations and explanations for flux rope self‐collimation, axial flows along flux ropes, eruption of arched flux ropes, strapping magnetic fields that inhibit eruption, the torus instability, and effects such as X‐ray emission of a kink‐driven secondary Rayleigh‐Taylor instability.
... [27][28][29][30][31] The GE with negative third order nonlinear term can be considered as a model equation to explain the physics of formation of double layers (which are formed due to net potential differences of electrostatic fields) observed in experiment [10][11][12] and in astrophysical plasma. [32][33][34][35][36][37][38][39] Presence of negative ions qualitatively modify the IAW group dynamics. The wave group dynamics are usually studied by the nonlinear Schrödinger equation (NLSE) or related model equations. ...
... The polarity of the double layer depends on the sign of 2 . The double layer solution given by (32) can also be considered as the kink (anti-kink) or non-dissipative shock waves. 60) ...
... The existence of strong electric currents owing to complex magnetic fields was noticed already several decades ago (Severnyi 1965;Alfvén & Carlqvist 1967). Although concerns were raised against the realism and feasibility of the calculation of these currents (Wilkinson et al. 1992;Parker 1996), when appropriate spectropolarimetric observations became commonplace, strong indications occurred that the inferred currents from Ampere's law are reasonably realistic and reflect true physical characteristics (Leka et al. 1996;Semel & Skumanich 1998;Wheatland 2000;Georgoulis et al. 2012). ...
Article
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We study the evolution of electric currents during the emergence of magnetic flux in the solar photosphere and the differences exhibited between solar active regions of different Hale complexity classes. A sample of 59 active regions was analyzed using a method based on image segmentation and error analysis to determine the total amount of nonneutralized electric current along their magnetic polarity inversion lines. The time series of the total unsigned nonneutralized electric current, I NN,tot , exhibit intricate structure in the form of distinct peaks and valleys. This information is largely missing in the respective time series of the total unsigned vertical electric current I z . Active regions with δ -spots stand out, exhibiting a 1.9 times higher flux emergence rate and 2.6 times higher I NN,tot increase. The median value of their peak I NN,tot is equal to 3.6 × 10 ¹² A, which is more than three times higher than that of the other regions of the sample. An automated detection algorithm was also developed to pinpoint the injection events of nonneutralized electric current. The injection rates and duration of these events were higher with increasing complexity of active regions, with regions containing δ -spots exhibiting the strongest and longest events. These events do not necessarily coincide with increasing magnetic flux, although they exhibit moderate correlation. We conclude that net electric currents are injected during flux emergence but are also shaped drastically by the incurred photospheric evolution as active regions grow and evolve.
... Among these solutions, the purely real solution of physical interest is the double layer solution when α 3 < 0. Physically this mean the negative ions are able to build up the effect of charge separation that is required to maintain and support the electric field for double layer structures. The net potential differences of electrostatic field are responsible for this kind of structure [45]. Titan's ionosphere (where negative ion plasma exists) consists of carbon bearing organic materials [2,3] and these interact with the double layer structures. ...
Article
The nonlinear dynamics of three-dimensional ion acoustic waves near critical density in plasmas consisting of electrons, positive and negative ions in the presence of a uniform external magnetic field are investigated. In the weak nonlinear and dispersive limit, the nonlinear wave is shown to be governed by a Gard-ner-Zakharov-Kuznetsov (GZK) equation, which is also shown to be integrable in the sense of Painlevé only on the traveling wave frame. The invariant Painlevé analysis provides the analytical solutions in the closed form of solitary, cnoidal, double layer and bipolar structures. The Lyapunov stability analysis shows that the stationary solitary structure is always unstable due to the three-dimensional effect. Finally, the stability of one-dimensional solitary wave has been checked in the transverse direction and the regions of stability (and instability) have been separated in terms of parameters. The results are in qualitative agreement with the observations in magnetized plasmas with negative ions.
... The existence of strong electric currents owing to complex magnetic fields was noticed already several decades ago (Severnyi 1965;Alfvén & Carlqvist 1967). Although concerns were raised against the realism and feasibility of calculation of these currents (Parker 1996;Wilkinson et al. 1992), when appropriate spectropolarimetric observations became commonplace, strong indications occurred that the inferred currents from Ampere's law are reasonably realistic and reflect true physical characteristics (Leka et al. 1996;Semel & Skumanich 1998;Wheatland 2000;Georgoulis et al. 2012). ...
Preprint
Full-text available
We study the evolution of electric currents during the emergence of magnetic flux in the solar photosphere and the differences exhibited between solar active regions of different Hale complexity classes. A sample of 59 active regions was analyzed using a method based on image segmentation and error analysis to determine the total amount of non-neutralized electric current along their magnetic polarity inversion lines. The time series of the total unsigned non-neutralized electric current, INN,totI_{NN,tot}, exhibit intricate structure in the form of distinct peaks and valleys. This information is largely missing in the respective time series of the total unsigned vertical electric current IzI_z. Active regions with δ\delta- spots stand out, exhibiting 1.9 times higher flux emergence rate and 2.6 times higher INN,totI_{NN,tot} increase. The median value of their peak INN,totI_{NN,tot} is equal to 3.610123.6\cdot10^12 A, which is more than three times higher than that of the other regions of the sample. An automated detection algorithm was also developed to pinpoint the injection events of non-neutralized electric current. The injection rates and duration of these events were higher with increasing complexity of active regions, with regions containing δ\delta-spots exhibiting the strongest and longest events. These events do not necessarily coincide with increasing magnetic flux, although they exhibit moderate correlation. We conclude that net electric currents are injected during flux emergence, but are also shaped drastically by the incurred photospheric evolution, as active regions grow and evolve.
... An electromotive force (EMF) that drives the circuit is generated in the convection zone by turbulent convective flows. As a result of the EMF, a current flows through the coronal loop as one component of the electric circuit (analogous to an illustration of Alfvén & Carlqvist 1967). In the corresponding electric circuit, Ionson (1984) shows that a coronal loop of length L in which the mean Alfvén speed is 〈V a 〉 can be described by lumped parameters characterizing the equivalent inductance, capacitance, and resistance of the circuit. ...
Article
The efficiency of coronal heating ε (cor) in a star can be quantified by L X / L bol , i.e., the ratio of X-ray luminosity to bolometric luminosity. The efficiency of chromospheric heating in the same star ε (chr) is typically assumed to be proportional to L (H α )/ L bol or L (Ca K)/ L bol where the lines H α and Ca K are often the two strongest emission lines in the visible spectrum: the constant of proportionality ( η = ε (chr)/[ L (H α )/ L bol ] > 1) includes contributions from many other lines emitted by the chromosphere. In the case of the quiet Sun, it has been known for decades that, in the Sun, the efficiency of chromospheric heating is larger by a factor of ε (chr)/ ε (cor) > 10 than the efficiency of coronal heating. Over the intervening years, data pertaining to ε (cor) and ε (chr) have been estimated for an increasingly large sample of main-sequence stars with spectral types later than the Sun. These data suggest that among M dwarfs, the efficiency ratio ε (chr)/ ε (cor) may in some stars become smaller than in the solar case. The effect of this is such that the value of ε (cor) may become comparable to the value of ε (chr). Here, we seek to understand why coronal heating may be >10 times more efficient (relative to chromospheric heating) in certain M dwarfs than in the Sun. Using data on coronal loop properties in flaring stars, we examine the hypothesis that in M dwarfs, the enhanced efficiency of coronal heating may be related to resonant coupling between coronal loops and the source of mechanical energy in the convection zone.
... This was theoretically discussed by Melrose (1991Melrose ( , 1995Melrose ( , 1996 and agrees with some results of numerical modeling (Török et al. 2014;Georgoulis 2018;Schmieder & Aulanier 2018;Russell et al. 2019). In particular, this makes it possible to describe CMEs and solar flares in terms of the torus instability (Myers et al. 2015;Chen 2017;Liu 2020) and circuit model (Alfvén & Carlqvist 1967;Spicer 1981;Zaitsev & Stepanov 1992), respectively. In spite of that, the issue on the relationship between twisted coronal loops and electric currents was not considered in detail. ...
Article
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Based on linear magnetohydrodynamic equations and an energy principle we analyze the ideal kink instability of a twisted force-free coronal loop (flux rope) surrounded by an outer potential magnetic field by using the sharp-boundary approximation at the surface. Unlike Tsap et al., a magnetic flux rope with nonneutralized (uncompensated) electric current is considered. We have shown that the twist angle of magnetic field lines is closely related to coronal mass ejections and solar flares. The kink instability condition does not depend on the radial profile of the magnetic field inside a flux rope in the long-wavelength limit but depends strongly on the reverse electric currents at the surface. The total critical twist angle of magnetic field lines, which determines the kink instability threshold, can be much greater than π radians due to reverse azimuthal surface current. This agrees with observations and illustrates the importance of the role of reverse currents for stabilization of a flux rope. Additional arguments in favor of the energy release models based on the uncompensated electric currents are presented.
... Here, ω e and ω i are gyrofrequencies of electrons and ions, ν ea and ν ia are electron-atom and ion-atom collision frequencies. Thus, the coronal magnetic loop with the photospheric current channel is an equivalent RLC-circuit [18][19][20]. In the self-consistent equation of the equivalent electric circuit, the resistance R and capacitance C are found to be dependent on the electric current [21]: ...
Article
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We study the origin of unusually persistent microwave and X-ray radiation from the ultracool dwarf TVLM 513-46546. It is shown that the source of ≈1 keV X-ray emission is not the entire corona of the brown dwarf, but a population of several hundreds of coronal magnetic loops, with 10 MK plasma heated upon dissipation of the electric current generated by the photospheric convection. Unlike models, which assume a large-scale magnetic structure of the microwave source, our model suggests that the microwave radiation comes from hundreds of magnetic loops quasi-uniformly distributed over the dwarf’s surface. We propose a long-term operating mechanism of acceleration of electrons generating gyrosynchrotron radio emission caused by oscillations of electric current in the magnetic loops as an equivalent RLC circuit. The second population of magnetic loops—the sources of microwave radiation, is at the same time a source of softer (≈0.2 keV) X-ray emission.
... To understand the various characteristics of BEN, Mace et al [15] reported the nonlinear propagation of EA waves. Analysis of double layers in plasma has generated a good deal of enthusiasm over a period of time in view of its congruity in cosmic applications [16][17][18]. A double layer (DL) comprises two oppositely charged parallel layers resulting in a strong electric field across the layer and can accelerate the electrons and ions in opposite directions thereby producing an electric current. ...
Article
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In the present research paper, propagation attributes of nonlinear electron-acoustic (EA) waves have been investigated in an unmagnetised plasma system consisting of cool fluid electrons and hot electrons observing the hybrid Cairns–Tsallis distribution. Sagdeev pseudopotential method has been used to explore the occurrence of large-amplitude solitons and double layers, focussing on how their characteristics depend upon different parameters. The analysis is further extended to examine the dynamics of large- and small-amplitude double layers. It is revealed that the present plasma system supports the existence of negative potential solitons and double layers in certain region of parameter space. The numerical results show that the Cairns–Tsallis-distributed hot electrons may affect the spatial profiles of EA waves and double layers. The present investigation may be relevant to the observation from Viking satellite in the dayside auroral zone.
... Acceleration of charged particles by current disruptions has been often observed in the Earth's magnetosphere [28,29], laboratory plasma jets [30], and tokamaks [31]. The interruption of current was also one of the earliest hypotheses explaining the origin of solar flares [32][33][34][35]. As for z-pinches and dense plasma foci, there could be miscellaneous causes of the current disruption (implosion of necks [8,[36][37][38][39][40][41], anomalous resistivity [42][43][44][45][46], etc). ...
Article
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Acceleration of ions to multi-MeV energies is investigated in various plasma devices to better understand processes in astrophysical plasmas and to develop efficient accelerators for a variety of applications. This paper reports the production of proton, deuteron, and electron beams in a z-pinch—a cylindrically symmetric plasma column that is compressed by its own magnetic field. For this work, the GIT-12 pulsed-power generator was used to drive a novel configuration of z-pinch that dramatically enhanced ion acceleration associated with disruption of the current by instabilities in the compressed plasma. During the disruption of 3 MA current, hydrogen ions were accelerated up to at least 50 MeV, which is almost a hundred-times the ion energy provided by the generator driving voltage of 0.6 MV. Under optimal conditions, the total numbers of hydrogen ions with energies above 20 and 50 MeV were 4 × 10 ¹³ and 10 ¹¹ , respectively. Accelerated deuterons produced one 20 ns (full width at half maximum) pulse of fast neutrons via D(d, n) ³ He and other nuclear reactions. A maximum neutron output of (1.0 ± 0.2) × 10 ¹² neutrons/sr was observed downstream, i.e., in the anode to cathode direction. In this direction, the maximum neutron energy reached 58 ± 7 MeV. Both ion and neutron beams in our experiment reached an end-point energy of about 60 MeV, which is the highest value observed in pulsed-power devices. A localized peak voltage of ≳60 MV was driven by the inductive energy that was stored around the plasma column and that was extracted during a sub-nanosecond current drop. Considering the natural occurrence of current-carrying columns in laboratory and space plasmas, the current interruption observed in z-pinches could represent a more general physical process that contributes to the efficient conversion of magnetic energy into the energy of particle beams in various plasmas.
... Such type of nonlinear structures has been found in different space environments such as magnetospheric plasmas [24], auroral plasmas [25], plasma sheet of Earth's magnetosphere [26] etc., and laboratory plasmas [27]. In the last few years, DLs have attracted much attention from research teams due to their wide range of applications in the study of flares, accelerations of charged particles etc [27,28]. Lotekar et al [29] explored electron acoustic DLs in the Earth's magnetospheric region. ...
Article
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Nonlinear structures associated with the kinetic Alfvén waves such as double layers (DLs) are investigated in a multicomponent plasma consisting of cold ions with superthermal electrons and positrons. The Sagdeev potential has been derived using two-potential theory in a low-β case. It is shown that our current consideration supports both compressive and rarefactive DLs. The effects of positron concentration and superthermality on DLs are studied. It is shown that the characteristics of the kinetic Alfvénic DLs, i.e., their profile is significantly modified due to superthermality and positron concentration. Our present investigation could be useful for understanding the kinetic Alfvénic DLs in the electron-positron-ion plasma with kappa distributed electrons and positrons.
... Low-frequency double layer (DL) has been extensively studied due to its relevance in the tandem mirror devices, [19] turbulence heating devices, [20] and in cosmic applications. [21,22] Employing the Sagdeev pseudo-potential approach and perturbation methods, various studies are reported on low-frequency DLs under different plasma configurations. [23][24][25][26] Small, finite-amplitude DLs are studied in ref. 27 adopting nonextensive electron distribution. ...
Article
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In the present article, we studied the effect of nonthermal electrons on the formation and existence of double‐layer structures in a three‐species plasma consisting of positive ions, nonthermal electrons, and immobile negative dust‐charged grains. Employing the reductive perturbations, a modified Korteweg–de Vries (mKdV) type equation is derived for the dust‐ion‐acoustic waves (DIAWs) bearing nonthermality. We found that both positive and negative polarity shock structures (double layer) can exist such that it switches polarity while changing the dust charge concentrations. However, strong nonthemality favours only rarefactive structures irrespective of the ion temperature. It is also found that increasing the nonthermal electron in the system the width of the double layer is increased; furthermore, the shock structure forms with small dust charge concentration. For small ionic temperature, increasing the nonthermal electrons in the system makes the double layer potential to increase; however, for σ = 1 reverse phenomena occurs. Our results are relevant to the shock observations in Q machine experiments and in the ionospheric regime of the earth.
... Moreover, it was recently shown that PVEC integrated over some parts of the flare regions linked to the flare ribbons near the PIL have a tendency to increase abruptly and stepwise during some flares (Janvier et al. 2014(Janvier et al. , 2016Sharykin & Kosovichev 2015;Wang et al. 2018). These observations are not consistent with electric-circuit-type models (Alfvén & Carlqvist 1967;Colgate 1978;Zaitsev & Stepanov 2015;Zaitsev et al. 2016), where nonthermal electrons are assumed to be localized in magnetic loops with the strongest electric currents, and the latter must dissipate, at least in part, during flares. Rather, they support the concept that processes of flare energy release and acceleration of particles occur in coronal reconnection regions above the photospheric PIL. ...
Article
This work is a continuation of Paper I and is devoted to the analysis of nonthermal electron dynamics and plasma heating in the confined M1.2 class solar flare SOL2015-03-15T22:43, revealing energy release in the highly sheared interacting magnetic loops in the low corona, above the polarity inversion line (PIL). The aim of the present work is to perform the first extensive quantitative analysis of the photospheric magnetic field and photospheric vertical electric current (PVEC) dynamics in the confined flare region near the PIL using new vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory with a high temporal resolution of 135 s. Data analysis reveals sharp changes of the magnetic structure and PVEC associated with flare onset near the PIL. It is found that the strongest plasma heating and electron acceleration are associated with the largest increase in the magnetic reconnection rate, total PVEC, and effective PVEC density in the flare ribbons. Observations and nonlinear force-free field extrapolations show that the magnetic field structure around the PIL is consistent with a tether-cutting magnetic reconnection (TCMR) geometry. We give a qualitative interpretation of the observed dynamics of the flare ribbons, magnetic field, PVEC, and electron acceleration within the TCMR scenario.
... Some of the non-potential "free energy" appears to remain in the corona even after a major flare, consistent with the idea that the current systems associated with the energy storage link the solar subsurface regions and the corona (Wang et al. 1994). Such currents persist and cannot change rapidly; thus the energy release comes from a restructuring of these currents (e.g., Melrose 1995Melrose , 2017, rather than from their interruption (Alfvén & Carlqvist 1967). Sun et al. (2012) provided an example of this current-displacement behavior during the X-class flare SOL2011-02-15. ...
Preprint
In a new finding, the waiting times between successive solar flares correlate strongly with their magnitudes, for events occurring within single isolated active regions. The time interval after the flare, rather than before, shows the correlation. implying a saturation of the free energy available. This finally establishes the build-up/release scenario for coronal flare energy storage. The lack of the before correlation (expected from a reset of the free energy) also confirms that the post-event structure retains significant free energy after each flare.
... Moreover, it was shown recently that the photospheric vertical electric currents integrated over the flare regions near the PIL has tendency to increase abruptly and stepwise during some flares (Janvier et al. 2014;Janvier et al. 2016;Wang et al. 2018). These observations are not consistent with the electric circuit type models (Alfvén & Carlqvist 1967;Colgate 1978;Zaitsev & Stepanov 2015;Zaitsev et al. 2016). Rather they support the concept that the processes of flare energy release and acceleration of particles occur in the coronal reconnection regions above the photospheric PIL. ...
Preprint
This work is a continuation of Paper I (Sharykin et al. 2018) devoted to analysis of nonthermal electron dynamics and plasma heating in the confined M1.2 class solar flare SOL2015-03-15T22:43 revealing energy release in the highly sheared interacting magnetic loops in the low corona, above the polarity inversion line (PIL). The scope of the present work is to make the first extensive quantitative analysis of the photospheric magnetic field and photospheric vertical electric current (PVEC) dynamics in the PIL region using new vector magnetograms obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) with high temporal resolution of 135 s. Data analysis revealed sharp changes of the magnetic structure and PVEC associated with the flare onset near the PIL. It was found that the strongest plasma heating and electron acceleration were associated with the largest increase of the magnetic reconnection rate, total PVEC and effective PVEC density in the flare ribbons. Observations and non-linear force-free field (NLFFF) extrapolations have shown that the magnetic field structure around the PIL is consistent with the tether-cutting magnetic reconnection (TCMR) geometry. We gave qualitative interpretation of the observed dynamics of the flare ribbons, magnetic field and PVEC, and electron acceleration, within the TCMR scenario.
... The electric universe theory studies the importance of electrical interactions from the smallest of particles to the largest galaxies in the universe, with supporting evidence that "electricity" appears to be everywhere [1,2,3,4,5]. In our recent paper Particles of the Universe Meets the Electric Universe, we apply the concept of wave energy to Ohm's Law to derive properties of the universe, illustrating that it indeed has electrical properties [6]. ...
Preprint
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In this paper, the two distinct properties of particle mass and charge are related, unifying equations for classical mechanics and electromagnetism that use mass and charge as variables for the electron.
... For example, "circuit models" for solar flares prescribed the total current I as it is in laboratory experiments (see e.g. Alfvén & Carlqvist 1967;Spicer 1982). More generally, one approach to plasma physics that is often used in the magnetospheric community (and is advocated by e.g. ...
Preprint
The chapter "Solar Active Region Electric Currents Before and During Eruptive Flares" is a discussion on electric currents in the pre-eruption state and in the course of eruptions of solar magnetic structures, using information from solar observations, nonlinear force-free field extrapolations relying on these observations, and three-dimensional magnetohydrodynamic (MHD) models. The discussion addresses the issue of neutralized vs. non-neutralized currents in active regions and concludes that MHD models are able to explain non-neutralized currents in active regions by the existence of strong magnetic shear along the polarity inversion lines, thus confirming previous observations that already contained this result. The models have also captured the essence of the behavior of electric currents in active regions during solar eruptions, predicting current-density increases and decreases inside flare ribbons and in the interior of expanding flux ropes respectively. The observed photospheric current density maps, inferred from vector magnetic field observations, exhibit similar whirling ribbon patterns to the MHD model results, that are interpreted as the signatures of flux ropes and of quasi-separatrix layers (QSLs) between the magnetic systems in active regions. Enhancement of the total current in these QSLs during the eruptions and decreasing current densities at the footpoint of erupting flux ropes, has been confirmed in the observations.
Article
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In this manuscript, we developed an analytical model for double layer and unstable entropy formation in current-carrying turbulent plasma. In the presence of a strong axial current, ion acoustic turbulence can give rise to enhanced anomalous resistivity and inhibited thermal conductivity. This state of uniform turbulence is, however, shown to be unstable to a purely growing axial perturbation when v02υ/ve2>k2χ, where v0,ve,υ,and χ are the electron drift velocity, thermal velocity, collision frequency, and thermal conductivity, respectively. The temperature perturbation enhances the local resistivity of electrons and raises their heating rate, further enhancing the temperature perturbation. When this tendency overpowers the opposing effect of thermal conduction, the instability grows. The nonlinear state of this instability has been analyzed and its possible relevance to the experimental results with double layer formation in a long plasma column has been discussed.
Article
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In the late 80s of the 20th century, Crimean astronomers, studying the structure of transverse magnetic fields in active regions (ARs), discovered signs of the presence of large-scale vertical electric currents – global electric currents (Abramenko, Gopasyuk 1987). In 2018–2020, we finalized and adapted the method for detecting large-scale electric currents to the data of modern instruments for studying the Sun, and began studying their dynamics on time scales of 3–5 days (Fursyak et. al 2020). Our researches carried out during 2020–2023 showed that: 1) Large-scale electric currents with values of the order of ~ 10 ¹³ A exist in ARs with nonzero flare activity. 2) Large-scale electric currents extend to the upper layers of the solar atmosphere in one part of the AR, and close through the chromosphere and corona in the remaining part of the AR. This assumption for the AR NOAA 12192 is confirmed by the results of numerical simulations performed in 2016 (Jiang et al. 2016). 3) The greater the magnitude of the large-scale electric current, the higher the probability of occurrence of M- and X- class solar flares in the AR. 4) At the final stages of AR evolution, a nonzero large-scale electric current can have a stabilizing effect on the sunspot, preventing its decay by its own magnetic field. 5) Large-scale electric currents are involved in coronal heating processes. Ohmic dissipation of a large-scale electric current is one of the mechanisms of quasi-stationary heating of coronal plasma above the AR. Our research on large-scale electric currents and the processes in which they take part continues.
Article
The characteristic of electron-acoustic (EA) solitary waves is investigated in an unmagnetized collisionless plasma system comprising cold electrons, superthermal electrons which follow the regularized κ\kappa-distribution (RKD), and stationary ions. The nonlinear structures of EA waves (EAWs) are obtained using a modified Korteweg-de Vries (mKdV) equation derived through a reductive perturbation method. The effect of superthermal index κ\kappa, the hot/cold electron density ratio α\alpha and cut-off parameter β\beta on the nonlinear wave structures of EAWs is discussed. The results indicate that the presence of superthermal electrons has a fundamental effect on the nonlinear EA structure.
Article
Тhe article is devoted to analyses of solar flare SOL2012-04-27 emission in Hydrogen, Helium and Calcium spectral lines observed on horizontal solar equipment HSFA-2 in Ondˇrejov observatory. The integrated fluxes are calculated. The data collected are treated in the approach of the fast energy release followed by gas evaporation. The gas parameters are calculated with chromosphere conditions and spectral line self-absorption taken into account. Encompassing of six lines allows to reveal the temperature, density and extent of the gas with high degree of validity. The best agreement of the theory with observations is obtained in the model of the spread of inhomogeneous clouds, each of which has hot (T ≈ 18000 ÷ 19500 K) and cool regions (T ≈ 8000 ÷ 9000 K). On average, one cloud gives about ten percent of the total flux.
Article
The wealth of detailed observations on transport in turbulent plasmas that has become available over the last decade from laboratory experiments, in situ space craft observations and computer simulation demonstrates that in contrast to classical transport, the various steps in the analysis of anomalous transport, involving microscopic processes and the global dynamics, are closely coupled. It also points to many new, exciting, and truly anomalous phenomena. These statements apply especially to the highly dynamic processes connected with field aligned currents. The usually vast difference in time or length scales must allow for considerable simplications in the analysis, depending on the system at hand, but requires careful consideration of the microscopic or macroscopic physics that of necessity is to be treated in a simplified manner. This point is demonstrated by using a marginal stability approach in a numerical model for field aligned currents and electromagnetic coupling in an extended system. Its aim is to see how energy is supplied to a localized dissipation region from a distant generator and how this dissipation in turn affects the global electro-dynamic structure. In addition to the earth's auroral flux tubes, for which this model was primarily designed, these questions are of importance to other extended current systems in astrophysics. Microscopic processes supporting enhanced dissipation and leading to other truly anomalous processes such as acceleration of selected particle groups are then discussed in relation to the global problem.
Article
Electrodynamic models for the activity of galactic nuclei are shown to be current systems which can be examined in terms of equivalent circuits. The resulting inductive circuit which describes the coupling of the generator (black-hole and accretion disk) to the distant load (jet plasma) is prone to various instabilities. We consider the disruption of this current system and propose that ultra-energetic cosmic rays (E~10 ¹⁹ –10 ²¹ eV) could be produced during the discharges, which occur at distances of ~10 ¹⁶ –10 ¹⁸ cm from the central massive hole (M~10 ⁸ M). Such discharges will also produce variable γ-ray and X-ray activity and we discuss observations of Cen A in this regard.
Article
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There are two main properties of a shielded magnetic flux rope. The first is the net electric current through its cross-section should be zero, i.e. I=0I = 0. The second is the existence of a nonzero pressure of external magnetic field Bex2/8π{{B_{ex}^2} \mathord/ {8\pi }} in order to keep in balance the magnetic rope with the strong force free inner structure in a rarefied solar atmosphere. The first condition requires the existence of a special cylindrical surface within the magnetic flux rope on which the current density j changes sign, so that the direction of the current at the rope's periphery (return current) is opposite to the current at its axis (direct current). Numerical calculations have shown that, when the pressure Bex2/8π{{B_{ex}^2} \mathord/ {8\pi }}drops to a certain limit, an indefinite increase in the electric current density j and the force free parameter α\alpha takes place in the vicinity of this special surface resulting in a dissipative collapse of the system. Such a drop in Bex2/8π{{B_{ex}^2} \mathord/ {8\pi }} may happen due to a multitude of reasons with the most obvious reason being the uprise of an magnetic flux rope into rarefied layers of the chromosphere or corona. Due to the dissipative collapse a violent energy release begins in a thin azimuthal shell at the periphery of the twisted magnetic flux tube. On the basis of these properties of the force free magnetic flux rope, the problems of plasma instabilities excitation and coronal heating are discussed.
Article
In this paper we have discussed the consequence of superthermal electrons and negative ion concentration on the arbitrary amplitude ion-acoustic double layers (IA-DLs) for plasma comprising the hot negative and positive ions with kappa distribution electrons. The energy equation is deduced for ion acoustic waves using Pseudo potential technique. We have investigated different parametric regimes for the existence of rarefactive and compressive ion acoustic DLs. The existence of double layers in term of minimum and maximum Mach number has calculated numerically. The effect of spectral index k on the amplitude of DLs and depth of Sagdeev potential has been discussed in detail. From numerical analysis, it is found that the compressive DLs exist at low values of α and rarefactive double layer exist at higher values of α. On the other hand, the effect of ionic temperature ratio ( σ 1 and σ 2 ) plays significant role for the formation of double layer. Our analytical work also shows that the system supports coexistence of compressive and rarefactive DLs. It is also observed that the mass ratio μ affect the basic properties of DLs. We expect that the present results may be used to explain the ion-acoustic double layer in space plasma, where two ionic species and superthermal electrons are observed NO52.35g.
Article
The dynamic behavior of large amplitude ion-acoustic double layers in a plasma is investigated in the presence of two-temperature nonextensive electrons. The effects of physical parameters, such as the temperature and concentration of positive ions on the formation and structure of double layer are discussed. It is shown that the depth of the Sagdeev potential and the amplitude of both positive and negative ion-acoustic double layers sensitively depend on the temperature and the concentration of positive ions. The obtained results are also compared with the results of a similar Maxwellian plasma with warm ions and two (cold and hot) electron species.
Article
The effects of nonthermal electrons and ion beams on the ion acoustic double layers in warm ion plasma have been studied using the pseudopotential technique. Sagdeev potential of ion-acoustic wave in the plasma has been derived and the solution of ion acoustic double layers has been obtained. The critical value of nonthermal parameter of electrons for existence of double layers is obtained and discussed. The profiles of double layers in the plasma are drawn taking different values of density and temperature of ion beams, and the nonthermal parameter of electrons obeying the critical condition. It has been shown that both compressive and rarefactive double layers are excited in the plasma depending on the values of nonthermal electrons and ion beam parameters. The width of double layers is also graphically discussed. The results are new and may be useful in understanding the acceleration processes of charged particles in space plasma.
Article
Laboratory reconnection experiments dedicated to problems of space and astrophysics are briefly reviewed with the purpose of demonstrating that such experiments can provide important insights of considerable value to the development of reconnection theory. Moreover, many of these insights are of a kind not likely to be perceived either when working directly with space observations or while pursuing a course of pure theoretical reasoning without reference to laboratory results.
Article
The reader is kindly asked to consider this report for some sort of greatly unbalanced equilibrium between the pressure exercised by the steadily increasing flow of papers discussing the vastly extending subject of solar activity, and the equally steady pressure exercised by the editor who insists on having this report twice as short as three years ago. Therefore, some selection of the subjects and papers had to be made, a fairly severe one, since only about one third of all published papers could have been mentioned in the references, and I am well aware that almost everyone who will read the report, could suggest some improvement of the selection scheme. Nevertheless, I believe that the report as it stands, can fulfill its basic purpose, i.e. to give to the readers a general picture on the progress, which has been achieved in the field of solar activity research since the Prague meeting and on some of the research activities which are in progress at the present time. It is a great pleasure to acknowledge the enormous help I have received from the authors of the individual sections of the Draft Report, as well as from many other members of the Commission, who have very kindly provided me, or the co-authors, with useful information on the recent progress of their work. It is necessary to add that some highly valuable comments made by V. Bumba, J. T. Jefferies, C. Sawyer, E. v. P. Smith, B. Valníček and J. M. Wilcox, have also been included in other chapters than those prepared by themselves.
Article
Electric currents play a critical role in the triggering of solar flares and their evolution. The aim of the present paper is to test whether the surface electric current has a surface or subsurface fixed source as predicted by the circuit approach of flare physics, or is the response of the surface magnetic field to the evolution of the coronal magnetic field as the MHD approach proposes? Out of all 19 X-class flares observed by SDO from 2011 to 2016 near the disk center, we analyzed the only nine eruptive flares for which clear ribbon hooks were identifiable. Flare ribbons with hooks are considered to be the footprints of eruptive flux ropes in MHD flare models. For the first time, fine measurements of the time evolution of electric currents inside the hooks in the observations as well as in the OHM 3D MHD simulation are performed. Our analysis shows a decrease of the electric current in the area surrounded by the ribbon hooks during and after the eruption. We interpret the decrease of the electric currents as due to the expansion of the flux rope in the corona during the eruption. Our analysis brings a new contribution to the standard flare model in 3D.
Article
Double layers associated with coupled ion-acoustic and drift modes are addressed in an inhomogeneous collision-less electron–ion magnetoplasma with Cairns–Tsallis velocity distribution, in the presence of stationary dust. The formation of double layers and their salient features are investigated by using Sagdeev potential technique. Further the effects of dust concentration, nonthermality and non-extensivity on double layers structure are studied. It is observed that the characteristics of nonlinear structures, i.e., double layers, are significantly modified in the presence of dust and superthermal particles.
Thesis
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The behavior and propagation of magnetohydrodynamic waves in optically thin astrophysical plasmas is investigated. First, the equations that define the magnetohydrodynamic waves [1] are enunciated: the continuity equations and the constitutive equations, where the Lorentz force for the magnetic field is also included in the respective equation of motion. Second, some dissipative processes for a plasma with given ionization are considered. For astrophysical applications in the original equations [2] to the set of conservation and constitutional equations, the heating and cooling functions are added. Subsequently, the linearization of the entire set of equations is carried out, which leads to the mathematical and numerical analysis of the secular dimensionless equations according to the corresponding case. Phase velocity and damping of magnetosonic waves are analyzed for typical temperatures in some cases of interest in Astrophysics, depending on the density and values of the magnetic field and their spatial orientation.
Article
There are still debates over whether particle acceleration in solar flares may occur due to interruption of electric currents flowing along magnetic loops. To contribute to this debate, we performed the first statistical study of relationships between flare hard X-ray (HXR; 50-100 keV) sources observed by the Ramaty High-Energy Solar Spectroscopic Imager and photospheric vertical electric currents (PVECs, jr) calculated using vector magnetograms obtained with the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We analyzed a sample of 48 flares from the C3.0 to X3.1 class and were observed in the central part of the solar disk by both instruments in 2010-2015. We found that ≍70% of all HXR sources overlapped with islands or ribbons of enhanced (| {j}r| > {10}4 statampere cm-2) PVECs. However, less than ≍40% of the HXR sources overlapped with PVEC maxima, with an accuracy of ±3″. In more than half of the flares, there were HXR sources outside of regions of enhanced PVECs. We found no correlation between the intensity of the HXR sources and PVEC density or total PVEC under them. No systematic dissipation of PVECs under the HXR sources was found during the flares. Collectively, the results do not support the current-interruption flare models. However, the results indicate the importance of the presence of longitudinal currents in flare regions. To understand their specific role in the processes of energy release, plasma heating, and acceleration of particles requires further investigation.
Article
The main problem of electromagnetic models of flares on the Sun is that in conditions of high electrical conductivity of the solar plasma it is difficult to provide an effective energy release as a result of Joule dissipation of currents in the “kernel of the flare”. In order to explain the rapid dissipation of electric currents in the “kernel of the flare”, we, within the framework of macroscopic magnetohydrodynamics, have considered the effect of reducing the electrical conductivity in a turbulent environment. The idea of redistribution of the electrical conductivity in groups of sunspots with complex magnetic field configuration is proposed. The proposed concept for the redistribution of electrical conductivity is based on the following physical effects and well-known observational conditions in the solar atmosphere. 1. Decreasing of the electrical conductivity (increase in the resistivity) in a turbulent environment. 2. Magnetic inhibition of the turbulence under the influence of magnetic fields. 3. Excitation of a large-scale electric field by macroscopic movements of the plasma in the photosphere in the presence of a weak general magnetic field of the Sun (photosphere dynamo). 4. Observed spatial heterogeneous structure of magnetic configurations in the vicinity of groups of sunspots, which leads to the formation of the current layers with the zero (neutral) magnetic fields. In the places of the zero magnetic field in the photosphere (which correspond to the “kernel of the flare”), where there is no suppression of turbulence by magnetism, the conductivity is turbulent in the nature. At the same time, in the vicinity of the sunspots outside the “kernel of the flare”, turbulent motions are largely suppressed by strong magnetic fields (B ≈ 3000 G), which almost alleviates the effect of the influence of turbulence on the conductivity of the plasma. Therefore, the electrical conductivity here will be gas-kinetic in the nature, the value of which greatly exceeds the turbulent conductivity. The turbulent conductivity calculated by us in the photosphere σ T ≈ 5 ⋅ 108 CGSE turned out to be 2-3 orders of magnitude smaller than the gaskinetic conductivity σ ≈ 1011 CGSE (in the places of strong magnetic fields). The discovered areas of the abnormal reduced turbulent conductivity in the places of the zero magnetic lines of complex configurations of the sunspot groups can contribute to the efficient dissipation of the electric currents, which provides efficient thermal energy release of the flares. The problem of circulation of two currents in the electric circuit of the corona-photosphere is briefly considered. According to the model of the photosphere dynamo, the convective movements on the photosphere level excite an electric field of magnitude E0 ≈ 10-4 CGSE. In this case, in external areas (in relation to the region of the “kernel of the flare”) of the electric circuit of the corona-photosphere in the places of strong magnetic fields, where the turbulence is almost suppressed, the value of the current will be ja = σ E0 ≈ 107 CGSE. At the same time, in the area of the “kernel of the flare”, where neutral magnetic fields do not affect turbulence, the current value will be much smaller: jT ≈ σ T E0 ≈ 5 ⋅ 104 CGSE. The existence of two sections with different currents in the electric circle of the corona-photosphere may contribute to the spatial division of charges, which in turn may be useful in the further development of the electromagnetic models of the flare.
Chapter
The Sun is our nearest star and the energy released by nuclear reactions near its center is transported by photons inside the inner 71%{\sim }71\% of the solar radius (R6.9×105R_\odot \simeq 6.9\times 10^5 km), called the radiative zone. Outside this radiative zone, called the convective zone, photons are no longer able to transfer energy efficiently, so convective instabilities set in and vertical flows carry nearly all the excess heat to the solar surface. This visible surface, called the photosphere, is the lowest layer of the solar outer atmosphere, emits almost all the solar light, and lowers its temperature by the radiation.
Article
An analytical and numerical investigation of the nonlinear evolution equations are exhibited with external magnetic field effects, the time derivative pressure expansion as well as other parameters like relativistic effect, mass variation, beam velocity and temperature effect have been taken into consideration. The presence of vortex like trapped electron distribution and positron beam governs the influence of soliton structure quite significantly. The present result should help us to understand the experiments that involve particle trapping and also the salient features of astrophysical environment like ionospheric plasma together with situations in plasma describing the electrostatic solitary structures usually seen in antimatter-related environment in interplanetary region.
Article
To overcome the difficulty in effective dissipation of currents in electromagnetic flare models associated with high gas-kinetic conductivity of the solar plasma, attention is given to the possibility of a local decrease in conductivity in the places of highly developed MHD turbulence near the neutral lines of photospheric magnetic configurations. The concept of redistribution of electrical conductivity, which is based on the following physical effects and conditions known from the observations in the solar atmosphere, is proposed: (1) A decrease in the electrical conductivity parameter (increase in the resistivity) in a turbulent medium. (2) Magnetic suppression of turbulence under the influence of strong magnetic fields. (3) Excitation of a large-scale electric field by macroscopic plasma motions in the photosphere in the presence of a magnetic field (photospheric dynamo). (4) The observable spatial inhomogeneous structure of magnetic configurations in the vicinity of sunspot groups, which leads to the formation of current layers with zero (neutral) magnetic fields lines. The calculated values of the MHD-turbulent conductivity near neutral magnetic lines in the photosphere turn out to be almost three orders of magnitude smaller than the values of the regular gas-kinetic conductivity in the places of strong magnetic fields in the vicinity of sunspots. A significantly reduced conductivity in the regions of highly developed MHD turbulence can contribute to accelerated Joule current dissipation, whose energy is consistent with the characteristics of thermal flares.
Article
I give here a short review of some of the main problems of the magnetic theories for the flare origin. I point out that the magnetic theories are unable to solve the problems of the energetics, height and compactness of the acceleration region, compresslve inflows, magnetic field structures, particle numbers, preflare upflows and the global cause of the flare origin. Then I outline the convective flare theory which have proposals for the solutions of these problems. I show here what is the role of the magnetic field at flare origins in the frame of the convective flare theory. The convective flare theory gives a deeper level understanding than the magnetic theories and therefore it also can supply us with the derivation of some input parameters and assumptions used for the magnetic theories and so it offers a wider perspective to understand the physics of the explosive astrophysical processes.
Article
Interruptions in inductive electric current circuits in the Sun are considered as possible causes of solar flares. The currents are assumed to have a filamentary structure and the interruption to be related to an instability well known in gas discharge physics.
Article
This paper is a review of our observational knowledge on solar magnetic fields. In Section 1 we make an attempt to summarize all observations of the general magnetic field (m.f.) of the Sun. Section 2 deals with the local m.f. at low latitudes and their connection with some features on the disk. The m.f. of sunspots and their peculiar character are considered in Section 3. The last section (4) is concerned with m.f. in sunspot groups, their changes and connections with solar activity.
Article
It is shown that high voltage surges are produced in apparatus associated with gas discharge devices when, and only when, the demand for current exceeds the current‐carrying capacity of the gas (or vapor). Cathode spot extinction and sputtering of hot cathodes cause only slight disturbances which do not produce high voltage in practical circuits. Experimental data on surge limits, i.e., the maximum currents that can be carried without surges, are given for four types of mercury vapor tube. These data lead to a single set of values of maximum current density as a function of vapor pressure, which may be used for the safe design of apparatus.
Cosmical Electrodynamics
  • H F~lthammar
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