Roles of Fast-Cyclotron and Alfvén-Cyclotron Waves for the Multi-Ion Solar Wind

Using linear Vlasov theory of plasma waves and quasi-linear theory of resonant wave–particle interaction, the dispersion relations and the electromagnetic field fluctuations of fast and Alfvén waves are studied for a low-beta multi-ion plasma in the inner corona. Their probable roles in heating and accelerating the solar wind via Landau and cyclotron resonances are quantified. In this paper, we assume that i) low-frequency Alfvén and fast waves, emanating from the solar surface, have the same spectral shape and the same amplitude of power spectral density (PSD); ii) these waves eventually reach ion cyclotron frequencies due to a turbulence cascade; iii) kinetic wave–particle interaction powers the solar wind. The existence of alpha particles in a dominant proton/electron plasma can trigger linear mode conversion between oblique fast-whistler and hybrid alpha–proton cyclotron waves. The fast-cyclotron waves undergo both alpha and proton cyclotron resonances. The alpha cyclotron resonance in fast-cyclotron waves is much stronger than that in Alfvén-cyclotron waves. For alpha cyclotron resonance, an oblique fast-cyclotron wave has a larger left-handed electric field fluctuation, a smaller wave number, a larger local wave amplitude, and a greater energization capability than a corresponding Alfvén-cyclotron wave at the same wave propagation angle θ, particularly at 80^°<θ<90^°. When Alfvén-cyclotron or fast-cyclotron waves are present, alpha particles are the chief energy recipient. The transition of preferential energization from alpha particles to protons may be self-modulated by a differential speed and a temperature anisotropy of alpha particles via the self-consistently evolving wave–particle interaction. Therefore, fast-cyclotron waves, as a result of linear mode coupling, constitute a potentially important mechanism for preferential energization of minor ions in the main acceleration region of the solar wind.     

The generation of solar type II radio bursts in coronal magnetic loops

It is shown that the existing theory of type II bursts, based on a model of the emission from the shock wave front, has difficulties when compared with observational data. We suggests a new model for type II bursts. According to this model, in an expanding magnetic loop a cluster of energetic electrons acts to excite the cyclotron instability of plasma waves. The waves are excited on surfaces where the cyclotron resonance condition is satisfied, and are then transformed into electromagnetic emission by merging. Our proposed model may be useful to explain some observational facts, such as the narrow-band character of the emission and the space-time relationship between the harmonics. Some tests to check the validity are proposed.     

On the saturation of electron-cyclotron masers in solar flares

We consider the relaxation of an unstable distribution of fast non-relativistic electrons. Langmuir turbulence generated by the electrons is found to determine the saturation of an electron-cyclotron maser. The important role of nonlinear processes in Langmuir and electromagnetic waves is shown. The characteristic saturation time is about 1 ms. It is shown that both cyclotron maser emission and the transformation of plasma waves to transverse ones can be essential in the formation of observable radio spectra from solar flares.     

Coherent synchrotron deceleration and the emission of type II and III solar radio bursts

Coherent synchrotron deceleration of 100 keV electrons is proposed as the mechanism by which type II and III solar radio bursts are generated. This mechanism directly excites the transverse electromagnetic radiation by a linear mechanism at the relativistic electron cyclotron frequency and at the first harmonic thereof if the energy spread of the exciting component is sufficiently narrow. Higher cyclotron harmonics are excluded by the energy spread in the 100 keV exciting electron component. This mechanism appears to fit the observational data concerning these emissions some-what better than the existing theory based on the non-linear interaction of electrostatic plasma waves.     

Proton cyclotron instability in the drifting magnetoplasma

A general expression for the tensor of the dielectrical susceptibility in an anisotropic plasma with particle drifts is derived, and the dispersion equation is found for waves propagating in arbitrary direction with respect to the mean magnetic field. The dispersion equation is solved for the case of electromagnetic ion‐cyclotron waves. It is found that in the plasma of the auroral magnetosphere strong plasma instability may occur so that the value of the growth rate of the waves is of the order of the wave frequency. Besides, the plasma instability is excited at less values of the wave number if the magnetospheric altitude becomes larger.     

Ion cyclotron waves,instabilities and solar wind heating

The effect of alpha particles on the dispersion relation of ion cyclotron waves and its influence on the heating of the solar wind plasma are investigated. The presence of alpha particles can dramatically change the dispersion relation of ion cyclotron waves, and significantly influence the way that ion cyclotron waves heat the solar wind plasma. We find that a spectrum of ion cyclotron waves affects the thermal anisotropy of the solar wind protons and other ions differently in interplanetary space: When alpha particles have a speed u _α>0.5v _A, and both protons and alpha particles have a thermal anisotropy T _⊥/T _∥>1, ion cyclotron waves heat protons in the direction perpendicular to the magnetic field, cool them in the parallel direction, and exert the opposite effect on alpha particles.     

Comparative study of ion cyclotron waves at Mars, Venus and Earth

Ion cyclotron waves are generated in the solar wind when it picks up freshly ionized planetary exospheric ions. These waves grow from the free energy of the highly anisotropic distribution of fresh pickup ions, and are observed in the spacecraft frame with left-handed polarization and a wave frequency near the ion’s gyrofrequency. At Mars and Venus and in the Earth’s polar cusp, the solar wind directly interacts with the planetary exospheres. Ion cyclotron waves with many similar properties are observed in these diverse plasma environments. The ion cyclotron waves at Mars indicate its hydrogen exosphere to be extensive and asymmetric in the direction of the interplanetary electric field. The production of fast neutrals plays an important role in forming an extended exosphere in the shape and size observed. At Venus, the region of exospheric proton cyclotron wave production may be restricted to the magnetosheath. The waves observed in the solar wind at Venus appear to be largely produced by the solar-wind-Venus interaction, with some waves at higher frequencies formed near the Sun and carried outward by the solar wind to Venus. These waves have some similarity to the expected properties of exospherically produced proton pickup waves but are characterized by magnetic connection to the bow shock or by a lack of correlation with local solar wind properties respectively. Any confusion of solar derived waves with exospherically derived ion pickup waves is not an issue at Mars because the solar-produced waves are generally at much higher frequencies than the local pickup waves and the solar waves should be mostly absorbed when convected to Mars distance as the proton cyclotron frequency in the plasma frame approaches the frequency of the solar-produced waves. In the Earth’s polar cusp, the wave properties of ion cyclotron waves are quite variable. Spatial gradients in the magnetic field may cause this variation as the background field changes between the regions in which the fast neutrals are produced and where they are re-ionized and picked up. While these waves were discovered early in the magnetospheric exploration, their generation was not understood until after we had observed similar waves in the exospheres of Mars and Venus.     

Influence of relativistic effects and vacuum polarization on the transfer of gyroresonance radiation and the stability of the atmospheres of compact stars

We consider the transfer of radiation and calculate the force of its pressure in the electron gyroresonance line in the atmospheres of magnetic degenerate stars. We specify the atmospheric parameters for which an outflow of plasma is possible under radiation pressure in the cyclotron line. We show that the permittivity tensor of a mildly relativistic plasma in a strong magnetic field found by applying relativistic corrections to the cyclotron resonance condition and by taking into account the vacuum polarization and recoil effects during photon scattering should be used to obtain proper results. We have determined the real and imaginary parts of the refractive indices and the polarization coefficients for normal electromagnetic waves when scattering dominates over absorption. Relativistic effects, which change greatly the dispersion and resonant absorption of waves propagating almost perpendicular to the magnetic field, and vacuum polarization have been found to change qualitatively the gyroresonance radiation spectrum and pressure for a wide range of parameters of stellar magnetospheres.     

Electromagnetic Ion Cyclotron Waves in Multi-Ions Hot Anisotropic Plasma in Auroral Acceleration Region-Particle Aspect Approach

Using particle aspect approach, the effect of multi-ions densities on the dispersion relation, growth rate, perpendicular resonant energy and growth length of electromagnetic ion cyclotron wave with general loss-cone distribution function in hot anisotropic multi-ion plasma is presented for auroral acceleration region. It is observed that higher He⁺ and O⁺ ions densities enhance the wave frequency closer to the H⁺ ion cyclotron frequency and growth rate of the wave. The differential heating of He⁺ ions perpendicular to the magnetic field is enhanced at higher densities of He⁺ ions. The waves require longer distances to achieve observable amplitude by wave-particle interactions mechanism as predicted by growth length. It is also found that electron thermal anisotropy of the background plasma enhances the growth rate and reduces the growth length of multi-ions plasma. These results are determined for auroral acceleration region.     

太阳射电米波毫秒快速尖峰辐射事件的统计分析

统计分析了云南天文台声光频谱仪在２２周峰年期间记录到的米波尖锋事件与光学活动及相关事件的关系。从它们的观测特征：短寿命,窄频带,频率快速漂移,及尖峰事件与磁结构复杂的大黑子活动区密切相关等,认为这些事件的辐射机制可能是电子回旋脉泽不稳定直接放大电磁波所致。     

Analysis methods for multi-component wave measurements on board the DEMETER spacecraft

We describe analysis methods to estimate parameters of electromagnetic waves based on the multi-component measurements of the DEMETER spacecraft. Using the fact that the wave magnetic field is perpendicular to the wave vector, the wave normal direction can be estimated by different methods. We use these plane-wave estimates to interpret measurements of the observed wave emissions. For instance, we use the recently developed singular value decomposition (SVD) technique. The results of the plane-wave analysis have an advantage that they often allow a straightforward interpretation. These different methods have been successfully tested with the data of previous spacecraft. All these methods are also implemented in the analysis tools designed for the analysis of the DEMETER wave measurements.We show the first results of these analysis techniques for different types of wave emissions observed on board DEMETER. Obliquely propagating right-hand polarized electromagnetic waves at a few hundreds of Hz are usually connected with a multi-ion mode structure below the local proton cyclotron frequency and with a sharp lower cutoff of left-hand polarized waves, as well as with right-hand polarized waves tunelling below the multi-ion cross-over frequency. Electron and proton whistlers are also very frequently observed on DEMETER. An unusual narrow-band emission at 140 Hz (well below the local proton cyclotron frequency) serves us as another case for a detailed analysis. We find that these waves are right-hand polarized and obliquely propagating.Using this example case, we also present analysis methods to estimate continuous distribution of wave energy density as a function of wave vector directions. These techniques of wave distribution function (WDF) analysis need both wave and particle measurements. In the analyzed case, two different methods of WDF analysis give similar results consistent with the results of the plane-wave techniques. To identify the source region we use the backward ray-tracing method. The wave normal direction obtained by the analysis of multi-component data is used for a simulation of wave propagation from the point of measurement. By this procedure, we obtain an inverse trajectory of the wave ray. We can thus follow the ray path back to the anticipated source region which is in our case located a few degrees of latitude to the South from the spacecraft position.     

OBLIQUE EMISSION OF WHISTLER-MODE WAVES AROUND INTERPLANETARY SHOCKS

We present a study of whistler-mode wave generation and wave particle interaction in the vicinity of interplanetary shocks as observed by the Ulysses spacecraft. Generally the whistler-mode waves (measured in the frequency range 0.22–448 Hz) are observed downstream of the shocks where they persist for some hours. From the electron distribution functions (EDF) in the energy range 1.6 to 862 eV measured by the spacecraft, we compute the wave growth rate of the electromagnetic electron cyclotron and Landau instabilities for the case of oblique propagation of the waves with respect to the interplanetary magnetic field (IMF) B. In general, in agreement with the wave measurements, the instability grows mostly downstream of the shock fronts. Following the wave activity, velocity space diffusion of the electrons results in a marginally stable state with some sporadic fluctuations.     

Polarization properties of low frequency electromagnetic cyclotron waves associated with magnetic clouds

Recent studies have revealed that there are a large number of low frequency electromagnetic cyclotron waves (ECWs) occurring in and around magnetic clouds (MCs) that are common magnetic structures in interplanetary space. Using magnetic field data from the STEREO spacecraft, this paper investigates polarization properties of ECWs associated with 120 MCs. Results show that the ECWs are highly transverse, strongly polarized waves with large ellipticities. Specifically, almost all of the waves take place with the ratios of transverse power to total power higher than 0.94, polarization degrees greater than 0.85, and ellipticities larger than 0.5. The mean values of these quantities can be up to 0.99, 0.96, 0.85, respectively. In particular, there is a tendency of ellipticities decreasing with respect to the wave normal angles for ECWs with left handed polarization. The decreasing tendency is consistent with the recent theory and simulation results.     

Stability of Electrostatic Electron Cyclotron Waves in a Multi-Ion Plasma

We have studied the stability of the electrostatic electron cyclotron wave in a plasma composed of hydrogen, oxygen and electrons. To conform to satellite observations in the low latitude boundary layer we model both the ionic components as drifting perpendicular to the magnetic field. Expressions for the frequency and the growth rate of the wave have been derived. We find that the plasma can support electron cyclotron waves with a frequency slightly greater than the electron cyclotron frequency ω _ce ; these waves can be driven unstable when the drift velocities of both the ions are greater than the phase velocity of the wave. We thus introduce another source of instability for these waves namely multiple ion beams drifting perpendicular to the magnetic field.     

On the generation of modified low‐frequency Farley‐Buneman waves in the solar atmosphere

The possibility of the excitation of Farley‐Buneman turbulence in the solar atmosphere is examined. It is found that the conditions for the generation of the modified Farley‐Buneman instability can be realized in the chromosphere of the Sun 1000 km above the photosphere. While usual Farley‐Buneman waves studied in relation to the Earth's ionosphere are almost electrostatic, the modified Farley‐Buneman waves in the solar atmosphere are electromagnetic ones. This means, that not only the potential electric field caused by the charge distribution, but also the perturbations of the magnetic field and the circularly‐polarized electric field are essential. Although the physical pictures of usual and modified Farley‐Buneman waves are different, their dispersion equations are almost the same. However, the increment of the modified Farley‐Buneman waves is varied by additional electromagnetic effects. It is demonstrated that electromagnetic effects hinder a Farley‐Buneman instability in occurring while ξ < 1, where ξ is the square of the ratio of ion plasma frequency times ion‐neutral frequency to ion‐cyclotron frequency times wave number times speed of light in vacuum. Under the condition ξ > 1, no Farley‐Buneman disturbances appear at all. In weakly‐ionized solar regions, the modified (ξ < 1) and also the usual (ξ ≪ 1) Farley‐Buneman turbulence could make “electromagnetic” contributions to the process of energy dissipation of nonstationary streams of neutral gases. Besides, they may modify the low‐frequency acoustic noise. It seems that the modified Farley‐Buneman turbulence contributes to the sporadic radiation of the Sun. It is possible, that such an effect takes not only place in the chromosphere of the Sun, but also in the atmospheres of other stars.     

Interaction of particles with ion cyclotron waves and magnetosonic waves. Observations from GEOS 1 and GEOS 2

Coordinated observations involving ion composition, thermal plasma, energetic particle, and ULF magnetic field data from GEOS 1 and 2 often reveal the presence of electromagnetic ion cyclotron and magnetosonic waves, which are distinguished by their respective polarization characteristics and frequency spectra. The ion cyclotron waves are identified by a magnetic field perturbation that lies in a plane perpendicular to the Earth's magnetic field B₀ and propagate along B₀. They are associated with the abundance of cold He⁺ in the presence of anisotropic pitch angle distributions of ions having energies E > 20 keV, and were observed at frequencies near the He⁺ gyrofrequency. The magnetosonic waves are characterized by a magnetic field perturbation parallel to B₀ and thus seem to be propagating perpendicular to the Earth's magnetic field. They often occur at harmonics (not always including the fundamental) at the proton gyrofrequency and are associated with phase-space-density distributions that peak at energies E ～ 5–30 keV and at a pitch angle of 90°. Such a ring-like distribution is shown to excite instability in the magnetosonic mode near harmonics of the proton gyrofrequency. Magnetosonic waves are associated in other cases with sharp spatial gradients in energetic ion intensity. Such gradients are encountered in the early afternoon sector (as a consequence of the drift shell distortion caused by the convection electric field) and could likewise constitute a source of free energy for plasma instabilities.     

Generation of electromagnetic radiation by an electron beam with a bump on the tail distribution function

This paper considers, in a linear approximation, the instability of a low-density electron beam propagating along the magnetic field of the solar corona, with respect to the excitation of electromagnetic (transverse) waves at cyclotron harmonics. It is shown that the extraordinary mode is excited at harmonics, beginning with the second and higher. Results of calculations check well with observed spectra of groups of solar spike radio bursts in the decimetric wavelength range.     

Origin of Jovian decameter wave emissions— Conversion from the electron cylotron plasma wave to the ordinary mode electromagnetic wave

Energy conversion rates from the extraordinary mode to the ordinary mode ofthe electromagnetic waves in the Jovian plasmasphere has been calculated for a model of the sharp boundary that is given in the vicinity of the position where ω = ω_p, for an angular frequency ω and the angular plasma frequency ω_p. The extraordinary mode electromagnetic wave that is obtained as a result of the transformation of a longitudinal propa- gating through an inhomogenous plasma is here considered. The results give conversion rates of 1–50 per cent, at the most, when a wave normal direction of an is nearly parallel to the boundary normal direction and when the Jovian magnetic field vector is close to the boundary normal direction within an angle range from 10° to 15°. The electric field intensity, in range from 7 to 70 mV/m, of the original electrostatic electron cyclotron plasma waves can give the power flux in a range from 10^-22 to 10^-20W/m² Hz for the Jovian decameter waves observed at the Earth's surface. Efficient energy conversion is possible only when the ray direction of the emitted wave is in nearly perpendicular direction with respect to the magnetic field; this is the origin of the sharp beam emission of the Jovian decameter wave burst.     

Parallel electric field-induced instability in the magnetospheric ion-electron plasma

A complete dispersion relation for a whistler mode wave propagation in an anisotropic warm ion-electron magnetoplasma in the presence of parallel electric field using the dispersion relation for a circularly polarized wave has been derived. The dispersion relation includes the effect of anisotropy for the ion and electron velocity distribution functions. The growth rate of electron-ion cyclotron waves for different plasma parameters observed atL = 6.6R _E has been computed and the results have been discussed in detail in the light of the observed features of VLF emissions and whistlers. The role of the combination of ion-cyclotron and whistler mode electromagnetic wave propagation along the magnetic field in an anisotropic Maxwellian weakly-ionized magnetoplasma has been studied.     

Pc 1–2 observations of heavy ion effects by synchronous satellite ATS-6

Ion cyclotron waves generated in the magnetosphere by the ion cyclotron instability of protons are thought to be the origin of Pc 1–2 geomagnetic pulsations. Propagation characteristics of these waves have been measured using ATS-6 synchronous satellite magnetometer wave data. Of particular interest are the wave spectra, polarization properties, and wave diagnostics; all are characteristic of propagation in a cool ambient magnetospheric plasma containing He⁺ and O⁺ heavy ions.