3D problem of the formation of smallscale density caverns with a nonstationary electric field in the region of auroral electric currents and kinetic Alfvén wave currents is considered. It is shown that an excess of the electron current velocity over a certain critical value of their thermal velocity is a probable cause of cavern formation. Linear and nonlinear stages of the density cavern formation are considered, and their main parameters are estimated. In the case of comparatively strong magnetic fields, caverns can be formed with comparable longitudinal and transverse (with respect to the magnetic field) scales. The properties of parameters of smallscale density caverns and nonstationary electric field agree with wellknown experimen tal data.
The preconditions for the formation of electron temperature jumps with scales comparable to the mean free path of electrons in the solar atmosphere are examined. In regions with heat flux, noise electric fields can arise due to ion-acoustic plasma turbulence. The well-known experimental data on heat flux from the corona to the chromosphere are used to calculate the height dependences of the threshold conditions for the occurrence of ion-acoustic instability. The calculations are conducted on the basis of well-known experimental data.
The vertical wave propagation in an inhomogeneous compressible atmosphere is studied in the framework of a linear theory. Under specific conditions imposed on atmospheric parameters, solutions can be found in the form of travelling waves with variable amplitudes and wave numbers that do not reflect in the atmosphere in spite of its strong inhomogeneity. Model representations for the sound speed have been found, for which waves can propagate in the atmosphere without reflection. A wave energy flux retains these reflectionless profiles, which confirms that energy can be transferred to high altitudes. The number of these model representations is fairly large, which makes it possible to approximate real vertical distributions of the sound speed in the Earth's atmosphere using piecewise reflectionless profiles. The Earth's standard atmosphere is shown to be well approximated by four reflectionless profiles with weak jumps in the sound speed gradient. It has been established that the Earth's standard atmosphere is almost completely transparent for the considered vertical acoustic waves in a wide range of frequencies, which is confirmed by observational data and conclusions derived using numerical solutions of original equations.
According to present-day ideas, nonlinear saturation of the astrophysical dynamo and, in particular, the solar dynamo, are based on the consideration of the magnetic helicity balance, to which the helicities of the large-scale magnetic field and small-scale field related to it contributed. We show that, in a mirrorasymmetric medium, the small-scale magnetic field generated by the small-scale dynamo also has a nonzero magnetic helicity, which also should be taken into account in the magnetic helicity balance.
The possibility of the existence of a solitary internal gravity wave at heights of the Earth’s thermosphere is considered. Analytical results were obtained in local approximation with weak nonisothermality of the atmosphere. For internal gravity waves, the Korteweg–de Vries equation was derived and studied with allowance for inhomogeneity, nonlinearity, and dissipation. The theoretical results were used to interpret the main parameters of solitary intermittent ionospheric disturbances observed at heights of the F region of the ionosphere.
We study the interaction between energetic protons of the Earth’s radiation belts and quasi-electrostatic whistler mode waves. The nature of these waves is well known: whistler waves, which are excited in the magnetosphere due to cyclotron instability, enter the resonant regime of propagation and become quasielectrostatic, while their amplitude significantly increases. Far enough from the equator where proton gyrofrequency and transversal velocity increase the nonlinear interaction between these waves and energetic protons becomes possible. We show that plasma inhomogeneity may destroy cyclotron resonance between wave and proton on the time scale of the order of particle gyroperiod which in fact means the absence of cyclotron resonance; nevertheless, the interaction between waves and energetic particles remains nonlinear. In this case, particle dynamics in the phase space has the character of diffusion; however, the diffusion coefficients are determined by the averaged amplitude of the wave field, but not by its resonant harmonics. For real parameters of the waves and magnetospheric plasma, proton pitch-angle diffusion leading to their precipitation from the magnetosphere becomes essential.
Satellite observations show that the electrostatic instability, which is expected to occur in most cases due to an inhomogeneous energy density caused by a strongly inhomogeneous transverse electric field (shear of plasma convection velocity), occasionally does not develop inside nonlinear plasma structures in the auroral ionosphere, even though the velocity shear is sufficient for its excitation. In this paper, it is shown that the instability damping can be caused by out-of-phase variations of the electric field and field-aligned current acting in these structures. Therefore, the mismatch of sources of free energy required for the wave generation nearly nullifies their common effect.
This work is devoted to the study of the generation of the equatorial noise—electromagnetic radiation below the LHR frequency observed near the equatorial plane of the magnetosphere at distances of ~4RE. According to accepted views, the generation of the equatorial noise is related to the instability of ring current protons. In this work, a logarithmic distribution of energetic protons over the magnetic moment with an empty loss cone is proposed, and arguments for the formation of such a distribution are presented. The main result of the work is the calculation and analysis of the instability increment of waves forming the equatorial noise. The increment obtained in this work significantly differs from that encountered in the literature.
In this paper, measurements of thermal and superthermal ions on the Interball-2 satellite are compared with the results of numerical simulation based on geomagnetic disturbances on December 7, 1996. It is shown that kinetic processes at small scales can have a significant effect on large-scale processes in high latitudes, leading to heating and the formation of ion fluxes and also to the formation of regions with an increased plasma density. Based on the analysis, the mechanisms that should be included in the large-scale ionosphere-magnetosphere models for the adequate description of the ion outflow from the ionosphere to the magnetosphere are determined.
The broadband electrostatic turbulence generally observed in the high-latitude ionosphere is a superposition of nonlocal waves of ion-acoustic and ion-cyclotron types. In the presence of a shear of ion parallel velocity, ion-acoustic modes can be induced by an instability emerging due to an inhomogeneous distribution of energy density. This paper is devoted to the studies of excitation of oblique ion-acoustic wave in background configurations with inhomogeneous profiles of both electric field and ion parallel velocity. A numerical algorithm has been developed, and instability was simulated at various parameters of background plasma. The general possibility of oblique ion-acoustic wave generation by a gradient of ion parallel velocity is shown. In this case, the wave spectrum is found to be broadband, which agrees with satellite observations.
The generation of the U- shaped spectrum, an unusual wave phenomenon observed in the equatorial part of the DEMETER satellite orbit, is studied. This wave phenomenon is explained for the first time based on the assumption that this emission is formed by the waves generated by lightning discharges, while the shape of the spectrum is determined by the features of wave propagation and damping in the near-equatorial region of the upper ionosphere.
The possibility of the existence of the solitary internal gravity waves on the Earth's thermosphere heights is discussed. Analytical results are obtained with local approximation weak nonisothermal atmosphere. For internal gravity waves is derived Korteweg-de Vries equation with the heterogeneity, nonlinearity and dissipation. Theoretical results are used to interpret the basic parameters of solitary traveling ionospheric disturbances observed at altitudes of F region of the ionosphere.
A 3D problem of the formation of smallscale density caverns with a nonstationary electric field in the region of auroral electric currents and kinetic Alfvén wave currents is considered. It is shown that an excess of the electron current velocity over a certain critical value of their thermal velocity is a probable cause of cavern formation. Linear and nonlinear stages of the density cavern formation are considered, and their main parameters are estimated. In the case of comparatively strong magnetic fields, caverns can be formed with comparable longitudinal and transverse (with respect to the magnetic field) scales. The properties of parameters of smallscale density caverns and nonstationary electric field agree with wellknown experimen tal data