Synthetic Spectra of the Fe VIII – Fe XVI Emission Lines for Electron Non-Thermal Distributions

A certain class of non-thermal electron distributions can exhibit more mono-energetic shape and a higher peak than the Maxwellian distribution. This type of electron distribution can be observed mainly in flaring plasmas. We have studied the influence of this kind of electron energy distribution on the excitation equilibrium of Fe VIII – Fe XVI in the solar corona. The changes in synthetic spectra of the emission lines belonging to these ions due to this non-thermal distribution are shown. The possibilities of finding the shape of the energy distribution function of electrons from the Fe line ratios are also discussed. The results can be used for diagnostics of coronal plasmas where the deviations of particle energy distributions from the Maxwellian one can be significant.     

The role of suprathermal particle measurements in CrossScale studies of collisionless plasma processes

The CrossScale mission will advance our understanding of fundamental plasma processes in collisionless plasmas. It will exploit the excellent natural plasma laboratory provided by the Earth’s magnetosphere and the near-Earth solar wind and, in particular, carry out multi-scale studies that will strongly complement plasma studies in ground-based laboratories. Previous studies of collisionless plasmas in space environments across the solar system have shown the ubiquitous nature of suprathermal particles and that these particles exhibit a power-law energy spectrum. In this paper we discuss the great significance of these suprathermal particles for CrossScale studies. We show that the presence of these particles is a natural consequence of the collisionless regime as they can propagate across the heliosphere with little spectral change and are not thermalised by collisions. They are a key indicator of the non-equilibrium nature of collisionless plasmas and an important source of free energy that can drive plasma processes. We discuss how these suprathermal particles influence the overall properties of the plasma. In particular, the energy distribution of particles follows a Kappa, rather than Maxwellian, distribution and thus the plasma does not have a single thermodynamic temperature. We also discuss the importance of the suprathermal tail as a tool to diagnose the processes responsible for particle energisation in collisionless plasmas. Such energisation is a common feature in collisionless plasmas, especially in terms of the primary science targets for CrossScale: reconnection, shocks and turbulence. Finally we also touch on the value of using CrossScale studies to provide ground truth measurements for a number of astrophysical techniques that exploit the effects of energetic electrons in the distant universe. Throughout the paper, we stress that suprathermal (30 keV-1 MeV) measurements are essential to fully characterise particle distributions. We show that such measurements will benefit greatly from the improved spatial and temporal resolution (compared to Cluster) that is proposed for the HEP instrument on CrossScale.     

Cylindrical Hall – MHD Waves: A Nonlinear Solution

The exact nonlinear cylindrical solution for incompressible Hall – magnetohydrodynamic (HMHD) waves, including dissipation, essentially from electron – neutral collisions, is obtained in a uniformly rotating, weakly ionized plasma such as exists in photospheric flux tubes. The ω – k relation of the waves, called here Hall – MHD waves, demonstrates the dispersive nature of the waves, introduced by the Hall effect, at large axial and radial wavenumbers. The Hall – MHD waves are in general elliptically polarized. The partially ionized plasma supports lower frequency modes, lowered by the factor δ≡ratio of the ion mass density to the neutral particle mass density, as compared to the fully ionized plasma (δ=1). The relation between the velocity and the magnetic field fluctuations departs significantly from the equipartition found in Alfvén waves. These short-wavelength and arbitrarily large amplitude waves could contribute toward the heating of the solar atmosphere.     

Three-Dimensional Particle Acceleration in Electromagnetic Dominated Outflows with Background Plasma and Clump

The effect of background plasma on particle acceleration via Poynting fluxes is studied in 3D PIC simulation of electron-positron and electron-ion plasmas. When a strongly magnetized ejecta at the center expands to low-temperature electron-positron ambient plasma background and a low-density clump, electromagnetic wave front accelerates particles in the background and clump, and captures them in the Ponderomotive potential well. We do not observe any instability, and the momentum distributions of background and clump form a power law of slope close to −1.5 with a sharp peak in the middle. When an ejecta expands to the ion-electron interstellar medium (ISM), the acceleration via Poynting flux is severely damped due to the charge separation.     

Magnetic Discontinuities in the Near-Earth Solar Wind: Evidence of In-Transit Turbulence or Remnants of Coronal Structure?

Fluctuations in the solar wind plasma and magnetic field are well described by the sum of two power law distributions. It has been postulated that these distributions are the result of two independent processes: turbulence, which contributes mainly to the smaller fluctuations, and crossing the boundaries of flux tubes of coronal origin, which dominates the larger variations. In this study we explore the correspondence between changes in the magnetic field with changes in other solar wind properties. Changes in density and temperature may result from either turbulence or coronal structures, whereas changes in composition, such as the alpha-to-proton ratio are unlikely to arise from in-transit effects. Observations spanning the entire ACE dataset are compared with a null hypothesis of no correlation between magnetic field discontinuities and changes in other solar wind parameters. Evidence for coronal structuring is weaker than for in-transit turbulence, with only ∼ 25% of large magnetic field discontinuities associated with a significant change in the alpha-to-proton ratio, compared to ∼ 40% for significant density and temperature changes. However, note that a lack of detectable alpha-to-proton signature is not sufficient to discount a structure as having a solar origin.     

Radio Observations of the 20 January 2005 X-class Flare

We present a multi-frequency and multi-instrument study of the 20 January 2005 event. We focus mainly on the complex radio signatures and their association with the active phenomena taking place: flares, CMEs, particle acceleration, and magnetic restructuring. As a variety of energetic-particle accelerators and sources of radio bursts are present, in the flare – ejecta combination, we investigate their relative importance in the progress of this event. The dynamic spectra of ARTEMIS-IV – Wind/Waves – HiRAS, with 2000 MHz – 20 kHz frequency coverage, were used to track the evolution of the event from the low corona to the interplanetary space; these were supplemented with SXR, HXR, and γ-ray recordings. The observations were compared with the expected radio signatures and energetic-particle populations envisaged by the Standard Flare – CME model and the reconnection outflow termination shock model. A proper combination of these mechanisms seems to provide an adequate model for the interpretation of the observational data.     

Universal characteristics of ion-acoustic wave dynamics in magnetized plasmas with emphasis on Tsallis distribution

Using the extended Poincaré-Lighthill-Kuo (PLK) reductive perturbation method, which incorporates the phase-shift variations, it is shown that common features on propagation and head-on collisions of ion-acoustic waves exist for a magnetized plasmas of different inertial-less particle distributions. For instance it is remarked that, the soliton amplitude is always independent of magnetic field strength while strictly depends on its angle regarding the propagation direction. Both types of solitons (compressive or rarefactive) are shown to exist which are defined through the critical angle γ=π/2 or other critical values depending on plasma fractional parameters. These critical plasma parameter values also define the sign of head-on collision phase shift. Furthermore, it is proved that for a given set of plasma parameters there is always a relative angle of propagation regarding to that of the magnetic-field for which the soliton width is maximum. Current findings apply to a wide range of magnetized plasmas including those containing background dust ingredients or two-temperature inertial-less particles and may be used to study laboratory or astrophysical magnetoplasmas.     

A Quick Method for Estimating the Propagation Direction of Coronal Mass Ejections Using STEREO-COR1 Images

We describe here a method to obtain the position of a coronal moving feature in a three-dimensional coordinate system based on height – time measurements applied to STEREO data. By using the height – time diagrams from the two SECCHI-COR1 coronagraphs onboard STEREO, one can easily determine the direction of propagation of a coronal mass ejection (i.e., if the moving plasma is oriented toward or away from the Earth). This method may prove to be a useful tool for space weather forecasting by easily identifying the direction of propagation as well as the real speed of the coronal mass ejections.     

3-D Rpic Simulations of Relativistic Jets: Particle Acceleration, Magnetic Field Generation, and Emission

We have applied numerical simulations and modeling to the particle acceleration, magnetic field generation, and emission from relativistic shocks. We investigate the nonlinear stage of theWeibel instability and compare our simulations with the observed gamma-ray burst emission. In collisionless shocks, plasma waves and their associated instabilities (e.g., the Weibel, Buneman and other two-stream instabilities) are responsible for particle (electron, positron, and ion) acceleration and magnetic field generation. 3-D relativistic electromagnetic particle (REMP) simulations with three different electron-positron jet velocity distributions and also with an electron-ion plasma have been performed and show shock processes including spatial and temporal evolution of shocks in unmagnetized ambient plasmas. The growth time and nonlinear saturation levels depend on the initial jet parallel velocity distributions. Simulations show that the Weibel instability created in the collisionless shocks accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The nonlinear fluctuation amplitude of densities, currents, electric, and magnetic fields in the electron-positron shocks are larger for smaller jet Lorentz factor. This comes from the fact that the growth time of the Weibel instability is proportional to the square of the jet Lorentz factor. We have performed simulations with broad Lorentz factor distribution of jet electrons and positrons, which is assumed to be created by photon annihilation. Simulation results with this broad distribution show that the Weibel instability is excited continuously by the wide-range of jet Lorentz factor from lower to higher values. In all simulations the Weibel instability is responsible for generating and amplifying magnetic fields perpendicular to the jet propagation direction, and contributes to the electron’s (positron’s) transverse deflection behind the jet head. This small scale magnetic field structure contributes to the generation of “jitter” radiation from deflected electrons (positrons), which is different from synchrotron radiation in uniform magnetic fields. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks. The detailed studies of shock microscopic process evolution may provide some insights into early and later GRB afterglows.     

Kinetic models for the exospheres of Jupiter and Saturn

The exospheric theory based on the Kappa velocity distribution function (VDF) is used to model the exosphere of the giant planets Jupiter and Saturn. Such Kappa velocity distribution functions with an enhanced population of suprathermal particles are indeed often observed in space plasmas and in the space environment of the planets. The suprathermal particles have significant effects on the escape flux, density and temperature profiles of the particles in the exosphere of the giant planets. The polar wind flux becomes several orders larger when suprathermal electrons are considered, so that the planetary ionosphere becomes then a significant source for their inner magnetosphere. Moreover, the number density of the particles decreases slower as a function of the altitude when a Kappa distribution is considered instead of a Maxwellian one. Two-dimensional maps of density are calculated for typical values of the temperatures. The exospheric formalism is also applied to study the escape flux from the exospheres of Io and Titan, respectively, moons of Jupiter and Saturn.     

Limits for the Firehose Instability in Space Plasmas

Electromagnetic instabilities in high-β plasmas, where β is the ratio of the kinetic plasma energy to the magnetic energy, have a broad range of astrophysical applications. The presence of temperature anisotropies T _∥ /T _⊥ >1 (where ∥ and ⊥ denote directions relative to the background magnetic field) in solar flares and the solar wind is sustained by the observations and robust acceleration mechanisms that heat plasma particles in the parallel direction. The surplus of parallel kinetic energy can excite either the Weibel-like instability (WI) of the ordinary mode perpendicular to the magnetic field or the firehose instability (FHI) of the circularly polarized waves at parallel propagation. The interplay of these two instabilities is examined. The growth rates and the thresholds provided by the kinetic Vlasov – Maxwell theory are compared. The WI is the fastest growing one with a growth rate that is several orders of magnitude larger than that of the FHI. These instabilities are however inhibited by the ambient magnetic field by introducing a temperature anisotropy threshold. The WI admits a larger anisotropy threshold, so that, under this threshold, the FHI remains the principal mechanism of relaxation. The criteria provided here by describing the interplay of the WI and FHI are relevant for the existence of these two instabilities in any space plasma system characterized by an excess of parallel kinetic energy.     

Cluster Observations of the Magnetospheric Low-Latitude Boundary Layer and Cusp during Extreme Solar Wind and Interplanetary Magnetic Field Conditions: I. 10 November 2004 ICME

We present a study of the magnetospheric cusp response to extreme external parameters during passage of the ICME over the Earth on 10 November 2004, based on Cluster observations of the plasma properties inside the low-latitude boundary layer (LLBL)/cusp regions. Two separate events are observed while Cluster is in the dawn sector, 07 – 08 h magnetic local time (MLT). First, a LLBL/cusp crossing occurs during a period of strong southward IMF. During this time, the LLBL/cusp is very small, ∼0.8 – 1° invariant latitude (ILAT) and moves equatorward, down to 67° ILAT. This can be explained by the occurrence of significant magnetopause erosion due to enhanced dayside sub-solar reconnection. The energy of the plasma inside this region is higher than normal, and the low-energy cut-off often observed in the ion data is also unusually high. This might be explained by the suggestion that the local magnetosheath Alfvén velocity and deHoffmann – Teller velocity are also both extremely high. However, the plasma convection and parallel velocity inside this region are not very high. The second event discussed in this paper is a LLBL/cusp crossing during strong equatorial IMF (mostly due to the dominant dawn – dusk component). Under these conditions, occurring at the same time as pulses of solar wind dynamic pressure, the observations are very complicated. However, we suggest that in the polar region of the southern hemisphere, Cluster cross two LLBLs/cusps, spatially separated by polar cap plasma. The first LLBL/cusp is formed by anti-parallel reconnection in the dusk sector of the southern hemisphere and the second is formed by anti-parallel reconnection in the dawn sector of the northern hemisphere. The second LLBL/cusp is located at extremely low latitude, less than ∼66.3° ILAT. During all LLBL/cusp crossings, strong ionospheric O⁺ ion outflow is detected in the form of a narrow beam with limited pitch-angle range.     

Streamer Belt and Chains as the Main Sources of Quasi-Stationary Slow Solar Wind

Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s⁻¹ and increased density N>10 cm⁻³, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit, between the fast solar wind flows (with a maximum velocity V _max≈450 – 800 km s⁻¹). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the contribution from the chains of streamers may be comparable to that from the streamer belt.     

Evolution of the Electron Distribution Function in the Whistler Wave Turbulence of the Solar Wind

The electron distribution functions from the solar corona to the solar wind are determined in this paper by considering the effects of the external forces, of Coulomb collisions and of the wave – particle resonant interactions in the plasma wave turbulence. The electrons are assumed to be interacting with right-handed polarized waves in the whistler regime. The acceleration of electrons in the solar wind seems to be mainly due to the electrostatic potential. Wave turbulence determines the electron pitch-angle diffusion and some characteristics of the velocity distribution function (VDF) such as suprathermal tails. The role of parallel whistlers can also be extended to small altitudes in the solar wind (the acceleration region of the outer corona), where they may explain the energization and the presence of suprathermal electrons.     

Coronal Mass Ejections,Magnetic Fields,and the Green Corona in Cycle 23

We study a time – latitudinal distribution of CMEs observed by the SOHO spacecraft, their projected speeds and associated magnetic fields, as well as the north – south (N – S) asymmetry of solar surface magnetic fields, and the coronal green line intensities. We have found that (a) there exists an intricate relation between the average projected velocity of CMEs and the mean value of large-scale magnetic fields; (b) there exists a pronounced N – S asymmetry in both the distribution and the number of CMEs; (c) this asymmetry is in favor of the northern hemisphere at the beginning of the cycle, and of the southern hemisphere from 2001 onward, being, in fact, (d) closely related with the N – S asymmetry in the distribution of large-scale magnetic fields and the coronal green line intensities.     

Manifestations of Magnetic Field Inhomogeneities

Both observations and simulations reveal large inhomogeneities in magnetic field distributions in diffuse plasmas. Incorporating these inhomogeneities into various calculations can significantly change the inferred physical conditions. In extragalactic sources, e.g., these can compromise analyses of spectral ageing, which I will illustrate with some current work on cluster relics. I also briefly re-examine the old issue of how inhomogeneous fields affect particle lifetimes; perhaps not surprisingly, the next generation of radio telescopes are unlikely to find many sources that can extend their lifetimes from putting relativistic electrons into a low-field ‘freezer’. Finally, I preview some new EVLA results on the complex relic in Abell 2256, with implications for the interspersing of its relativistic and thermal plasmas.     

Stream Interactions and Interplanetary Coronal Mass Ejections at 5.3 AU near the Solar Ecliptic Plane

We have performed a survey of the characteristics of two types of large spatial-scale solar-wind structures, stream interaction regions (SIRs), and interplanetary coronal mass ejections (ICMEs), near 5.3 AU, using solar-wind observations from Ulysses. Our study is confined to the three aphelion passes of Ulysses, and also within ± 10° of the solar ecliptic plane, covering a part of 1992, 1997 – 1998, and 2003 – 2005, representing three slices of different phases of the solar activity cycle. Overall, there are 54 SIRs and 60 ICMEs in the survey. Many are merged in hybrid events, suggesting that they have undergone multiple interactions prior to reaching Jovian orbit. About 91% of SIRs occur with shocks, with 47% of such shocks being forward – reverse shock pairs. The solar-wind velocity sometimes stays constant or even decreases within the interaction region near 5.3 AU, in contrast with the gradual velocity increase during SIRs at 1 AU. Shocks are driven by 58% of ICMEs, with 94% of them being forward shocks. Some ICMEs seem to have multiple small flux ropes with different scales and properties. We quantitatively compare various properties of SIRs and ICMEs at 5.3 AU, and study their statistical distributions and variations with solar activity. The width, maximum dynamic pressure, and peak perpendicular pressure of SIRs all become larger than ICMEs. Dynamic pressure (P _dyn) is expected to be important for Jovian magnetospheric activity. We have examined the distributions of P _dyn of SIRs, ICMEs, and general solar wind, but these cannot explain the observed bimodal distribution of the location of the Jovian magnetopause. By comparing the properties of SIRs and ICMEs at 0.72, 1, and 5.3 AU, we find that the ICME expansion slows down significantly between 1 and 5.3 AU. Some transient and small streams in the inner heliosphere have merged into a single interaction region. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Spatial Distribution of Oscillations in Faculae

We find that oscillations of the LOS velocity in Hα vary within facula regions. The power spectra show that the contributions of low-frequency modes (1.2 – 2 mHz) increase at the network boundaries. Three- and five-minute periods dominate inside cells. The spectra of photospheric and chromospheric LOS-velocity oscillations differ for most faculae. We detected several cases where oscillations in faculae seem to propagate horizontally with phase velocities of 50 – 70 km s⁻¹. Their location in space and time coincided with the local maximum of the longitudinal magnetic field.     

Electron acoustic double layers in a plasma with a <Emphasis Type="Italic">q</Emphasis>-nonextensive electron velocity distribution

Electron-acoustic double-layers (EA-DLs) are addressed in a plasma with a q-nonextensive electron velocity distribution. The domain of their allowable Mach numbers depends drastically on the plasma parameters and, in particular, on the electron nonextensivity. As the electrons evolve far away from their thermodynamic equilibrium, the negative EA-DLs shrinks and may develop into compressive EA-DLs. Our results may be relevant to the double-layers observed both in the auroral region and the plasma sheet of Earth’s magnetosphere (during enhanced magnetic activity). These DLs associated parallel electric fields are thought to be responsible for particle (electrons and ions) acceleration. Furthermore, our theoretical analysis brings a possibility to develop more refined theories of nonlinear cosmic DLs that may occur in astrophysical plasmas.     

等离子天体物理学与现代等离子体宇宙观

现代科学表明宇宙中99%以上的可观测物质都处于等离子体状态,从小尺度的微观粒子动力学集体过程与能量转换机制到大尺度的宇宙等离子天体结构状态与爆发活动现象,都是等离子天体物理学的研究课题.从宇宙演化历史、大尺度结构形成以及爆发活动现象等方面,系统地论述了等离子天体物理学在现代天文学发展以及现代等离子体宇宙观形成中的重要作用.同时,结合空间卫星科学探测研究及其对现代天文学的巨大影响,进一步阐述了地球磁层和日球层等空间等离子体实地探测研究在等离子天体物理学研究中所扮演的“天然实验室”的独特作用.