Auroral Kilometric Radiation as a Diagnostic Tool for the Properties of the Magnetosphere

JETP Letters - Auroral kilometric radiation is used as a tool for the remote diagnostics of processes in the Earth’s magnetosphere. Using satellite data and the spectrum of fluctuations of...     

Mid-Latitude Amplitude Scintillations of GPS Signals and GPS Failures at the Auroral Oval Boundary

Analyzing ionospheric effects of magnetic storms on July 15, 2000 and September 26, 2001, we show that a region with intense small-scale electron density irregularities emerges in the main phase of magnetic storms on the southern boundary of the auroral oval as it expands to the mid-latitudes. This assumption is supported by the presence of powerful backscattering signals recorded on July 15, 2000 by the incoherent-scatter radars in the eastern and western hemispheres. Such irregularities cause strong scintillations of signals of the navigation Global Positioning System (GPS), which leads to a breakdown of signal tracking and an increase in the positioning errors of the GPS.     

An Improved Model of the Jovian Magnetosphere

The Jovian magnetosphere is modulated by the solar wind and centrifugal force. The configuration of the magnetic field in the previous model of the magnetosphere including the centrifugal force is consistent with the observations at low magnetic latitude （Λ〈50°）, while there is a substantial difference between the results of the model and the observations at high magnetic latitude （Λ≥50°）, especially in the distant magnetotail. Based on the previous model, a new configuration of the Jovian magnetosphere in the night side is suggested by a three-step transformation in this study. The new magnetosphere obtained by the transformation method is flattened in the z-direction and stretched in the x-direction in distant magnetotail, which agree with general knowledge.     

Channeling of Auroral Kilometric Radiation During Geomagnetic Disturbances

JETP Letters - The electromagnetic fields measured on the ERG satellite are presented and their comparative analysis with measurements on the WIND satellite is carried out. The possibility of...     

Mode-Coupling and Nonlinear Landau Damping Effects in Auroral Farley-Buneman Turbulence

Abstract

The fundamental problem of Farley-Buneman turbulence in the auroral E-region has been discussed and debated extensively in the past two decades. In the present paper we intend to clarify the different steps that the auroral E-region plasma has to undergo before reaching a steady state. The mode-coupling calculation, for Farley-Buneman turbulence, is developed in order to place it in perspective and to estimate its magnitude relative to the anomalous effects which arise through the nonlinear wave-particle interaction. This nonlinear effect, known as nonlinear “Landau damping” is due to the coupling of waves which produces other waves which in turn lose energy to the bulk of the particles by Landau damping. This leads to a decay of the wave energy and consequently a heating of the plasma. An equation governing the evolution of the field spectrum is derived and a physical interpration for each of its terms is provided.     

Calculation of the Scattering Cross Section of Auroral Irregularities

Calculation of the scattering cross section per unit volume of auroral irregularities requires comprehensive knowledge of the law describing the formation of irregularities at both linear and nonlinear stages. In this paper, we calculate the scattering cross section using a simple idealized nonlinear model proposed by St.-Maurice and Schlegel. It is shown that the theoretical dependence of the scattering cross section per unit volume on the radar frequency calculated in terms of this model is in good agreement with the experimental curve.     

Regimes of Resonant Interactions of Electrons with Auroral Kilometric Radiation

Radiophysics and Quantum Electronics - We analyze the resonant interaction of energetic electrons with auroral kilometric radiation (AKR). Possible regimes of such an interaction are studied on the...     

自适应算法在极光系统参数估算中的应用

讨论带参数的自适应时域方法计算极光系统的参数,以一个有理形式函数模型来代表系统函数,采用可以在线实时应用的递推自适应算法来确定该模型的参数。利用这种方法处理测量所得的极光亮度数据,现用互谱方法计算的氧原子「ＯＩ３２」跃迁时Ｏ（＾１Ｓ）态的平均有效寿命符合得很好。     

Effects of Spatial Variation of Thermal Electrons on Whistler-Mode Waves in Magnetosphere

A ray-tracing method is developed to evaluate the wave growth/damping and specifically propagation trajectories of the magnetospherically reflected Whistler-mode waves. The methodology is valid for weak wave growth/damping when plasma is comprised of a cold electron population and a hot electron population, together with background neutralizing ions, e.g. protons. The effect of anisotropic thermal electrons on the propagation of Whistler-mode waves is studied in detail. Numerical results are obtained for a realistic spatial variation model of plasma population, including the cold electron density distribution, and the thermal electron density and temperature distribution. It is found that, analogous to the case of the typical cold plasma approximation, the overall ray path of Whistler-mode waves is insensitive to the thermal electron density and temperature anisotropy, and the ray path reflects where wave frequency is below or comparable to the local lower hybrid resonance frequency flhr. However, the wave growth is expected to be influenced by the thermal electron population. The results present a first detailed verification for the validity of the typical cold plasma approximation for the propagation of Whistler-mode waves and may account for the observation that the Whistler-mode waves tend to propagate on a particular magnetic shell L where the wave frequency is comparable to fthe.     

Bounce-Averaged Acceleration of Energetic Electrons by Whistler Mode Chorus in the Magnetosphere

We construct the bounce-averaged diffusion coefficients and study the bounce-averaged acceleration for energetic electrons in gyroresonance with whistler mode chorus. Numerical calculations have been performed for a band of chorus frequency distributed over a standard Gaussian spectrum specifically in the region near L = 4.5, where peaks of the electron phase space density occur. It is found that whistler mode chorus can efficiently accelerate electrons and can increase the phase space density at energies of about 1 MeV by more than one order of magnitude about one day, in agreement with the satellite observations during the recovery phase of magnetic storms.     

Theory of Generation of Discrete ELF/VLF Emissions in the Earth's Magnetosphere

We review the current state of studies related to the origin of discrete ELF/VLF emissions in the Earth's magnetosphere and discuss recent theoretical results concerning this problem.     

Plasma Processes Driven by Current Sheets and Their Relevance to the Auroral Plasma

Satellite and rocket observations have revealed a host of auroral plasma processes, including large dc perpendicular electric fields (E?) associated with electrostatic shocks, relatively weak parallel electric fields (E?) associated with double layers, upflowing ions in the form of beams and conics, downflowing and upflowing accelerated electron beams, several wave modes such as the electrostatic ion-cyclotron (EIC), lower hybrid (LH), very low frequency (VLF), extremely low frequency (ELF), and high-frequency waves and associated nonlinear phenomena. Recently, we have attempted to simulate the various processes using a two-dimensional particle-in-cell code in which the plasma is driven by current sheets of a finite thickness. Striking similarities between the observed auroral plasma processes and those seen in the simulations are found. In this paper we give a review of the plasma processes dealing with dc and ac electric fields, formation of ion beams and conics, and electron acceleration. Electrostatic shock-type electric fields (E?e) occur near the current sheet edges. Such fields arise because of the contact between the high-and low-density plasmas inside and outside the sheet, respectively. Double layers having upward electric fields form inside the sheet and they are distinguishable from the large perpendicular electric fields (E?e) only in wide sheets with thicknesses l >> ?i, the ion Larmor radius. Double layers with a reverse polarity form outside the sheet where downward currents flow. The most energetic ions are found to have pitch angles near 90°, implying a large perpendicular acceleration of the ions.     

Singlet molecular nitrogen in the Auroral ionosphere and under the conditions of laboratory discharge

Using the suggested model of the electron kinetics of N₂ singlet states, the population of the vibrational levels in the molecular nitrogen states (a′)¹Σ _u ⁻, a ¹Π _g , and w ¹Δ _u is calculated for the case when fast auroral electrons penetrate into the Earth’s ionosphere. It is shown for the first time that the population distribution of the vibrational levels v = 0−6 in the state a ¹Π _g in the auroral ionosphere and also in a laboratory discharge varies with atmospheric pressure insignificantly. Similar calculations for pure nitrogen atmosphere show a considerable increase in the populations of lower vibrational levels (v = 0−2) with rising pressure.     

Reformed Solitary Kinetic Alfven Waves due to Dissipations and Auroral Electron Acceleration

The physical nature of the auroral electron acceleration has been an outstanding problem in space physics for decades. Some recent observations from the auroral orbit satellites, FREJA and FAST, showed that large amplitude solitary kinetic Alfvén waves (SKAWs) are a common electromagnetic active phenomenon in the auroral magnetosphere. In a low-β (i.e., β/2<<m_e/m_i<<1) plasma, the drift velocity of electrons relative to ions within SKAWs is much larger than thermal velocities of both electrons and ions. This leads to instabilities and causes dissipations of SKAWs. In the present work, based on the analogy of classical particle motion in a potential well, it is shown that a shock-like structure can be formed from SKAWs if dissipation effects are included. The reformed SKAWs with a shock-like structure have a local density jump and a net field-aligned electric potential drop of order of m_ev_A²/e over a characteristic width of several λ_e. As a consequence, the reformed SKAWs can efficiently accelerate electrons field-aligned to the order of the local Alfvén velocity. In particular, we argue that this electron acceleration mechanism by reformed SKAWs can play an important role in the auroral electron acceleration problem. The result shows that not only the location of acceleration regions predicted by this model is well consistent with the observed auroral electron acceleration region of 1—2 R_E above the auroral ionosphere, but also the accelerated electrons from this region can obtain an energy of several keV and carry a field-aligned current of several μA/m² which are comparable to the observations of auroral electrons.     

Evolved Algorithm and Vibration Stability for Nonlinear Disturbed Security Systems

In this paper, a method sustaining system stability after decomposition is proposed. Based on the stability criterion derived from the energy function, a set of intelligent controllers is synthesized which is used to maintain the stability of the system. The sustainable stability problem can be reformulated as a Linear Matrix Inequalities (LMI) problem. The key to guaranteeing the stability of the system as a whole is to find a common symmetrically positive definite matrix for all subsystems. Furthermore, the Evolved Bat Algorithm (EBA) is employed to replace the pole assignment method and the conventional mathematical methods for solving the LMI. The EBA is utilized to find feasible solutions in terms of the energy equation. The experimental results show that the EBA is capable of providing proper solutions, which satisfy the sustainability and stability criteria, after a short period of recursive computing.