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Ion beams observed in the plasma sheet boundary layer (PSBL), cusp, and on the auroral zone field lines are expected to have spatial gradients in their drift velocity. Generation of kinetic Alfvén waves by velocity shear of the ion beams is discussed. It is shown that a hot ion beam can excite both a resonant kinetic Alfvén wave instability and a non-resonant coupled Alfvén-ion acoustic instability. For typical parameters, observed on the auroral field lines in the altitude range of 5–7 RE (where RE is the Earth’s radius), the frequency of the velocity shear modes, in the satellite frame of reference, lie in the ultra-low frequency (ULF) range. The noise due to velocity shear driven Alfvén modes is electromagnetic in nature, and has a finite parallel electric field component.  相似文献   

3.
We investigate electron acceleration due to shear Alfvén waves in a collissionless plasma for plasma parameters typical of 4–5RE radial distance from the Earth along auroral field lines. Recent observational work has motivated this study, which explores the plasma regime where the thermal velocity of the electrons is similar to the Alfvén speed of the plasma, encouraging Landau resonance for electrons in the wave fields. We use a self-consistent kinetic simulation model to follow the evolution of the electrons as they interact with a short-duration wave pulse, which allows us to determine the parallel electric field of the shear Alfvén wave due to both electron inertia and electron pressure effects. The simulation demonstrates that electrons can be accelerated to keV energies in a modest amplitude sub-second period wave. We compare the parallel electric field obtained from the simulation with those provided by fluid approximations.  相似文献   

4.
利用二维混合数值模拟研究了有速度驱动、低等离子体β值情况下的磁场重联过程,结果表明磁重联过程可以产生Alfven波,该Alfven波动对重新区中的新生离子作用,使得新生离子经历投掷角散射方程,具有球壳分布特征,部分新生离子得到加速,其获得的最大能量约为4(miVA0^2/2),此加速过程所需的加速时间在100/Ωi量级,是一个极快的加速机制,加速粒子能谱为双幂律谱。  相似文献   

5.
We calculate the maximum energy that a particle can obtain at perpendicular interplanetary shock waves by the mechanism of diffusive shock acceleration. The influence of the energy range spectral index of the two-dimensional modes of the interplanetary turbulence is explored. We show that changes in this parameter lead to energies that differ in at least one order of magnitude. Therefore, the large scale structure of the turbulence is a key input if the maximum particle energy is calculated.  相似文献   

6.
We have used the technique suggested by Hocking [Hocking, W. A new approach to momentum flux determinations using SKiYMET meteor radars. Ann. Geophys. 23, 2005.] to derive short period wind variances in the 80–100 km region from meteor radar data. We find that these fluctuating winds, assumed to correspond to gravity waves and turbulence, are closely correlated with the vertical shear of the horizontal tidal winds. This close correlation suggests that in situ wind shear may be a major source of gravity waves and turbulence in the MLT. If this is the case, gravity waves generated in the troposphere and propagating up to the MLT region, generally assumed to constitute an important influence on the climatology of the region, may be a less important source of energy and momentum in the 80–100 km region than has been hitherto believed.  相似文献   

7.
The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under consideration can be made are studied thoroughly. Ultra-high-energy CRs (up to 1020 eV) are shown to be obtained due to the surfing in relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs).  相似文献   

8.
Satellite observations have revealed solitary potential structures in the Earth’s magnetotail region. These structures have both positive (compressive) and negative (rarefactive) electrostatic potentials. In this paper we study the electron-acoustic solitary waves (EASWs) in an unmagnetized plasma consisting of cold plasma electrons and isothermal ions with two different temperatures. Using the reductive perturbation method, the nonlinear evolution of such structures is studied. The numerical computations are performed to study the role of two temperature ions in the generation of EASWs. In this case, the model supports the existence of both positive and negative electrostatic potentials with bipolar pulses. The electric field associated with these positive and negative solitary structures are numerically computed. The present study could be useful to construe the compressive and rarefactive electric field bipolar pulses associated with the BEN type emissions in the magnetospheric regions where the electron beams are not present.  相似文献   

9.
Within a quantum hydrodynamic model and using the reductive perturbation technique, the nonlinear ion-acoustic wave (IAW) excitations due to a moving charged object in an electron-pair-ion quantum plasma are studied both analytically and numerically. In such quantum plasmas we have derived forced Korteweg-de Vries (fKdV) type equation for finite amplitude nonlinear IAWs. The effect of relevant plasma parameters on solitonic excitations is investigated. Numerical simulation shows the generation of advancing solitons ahead of the forcing term traveling at a faster rate with trailing wakes behind the forcing disturbance. It is found that propagation characteristics of nonlinear excitations are significantly affected by quantum parameter. Additionally, we have pursued our analysis by extending it to account for arbitrary amplitude IA solitons, and derived a system of nonlinear differential equations which are analyzed numerically to study the dynamics. Nonlinear analysis predicts the existence of periodic and quasiperiodic nature of the nonlinear system and reveals that the transition from quasiperiodic to periodic behavior occurs due to the variation of quantum diffraction.  相似文献   

10.
In this paper, we show the potential of satellite altimetry to study the interaction of Rossby waves with the shear flow. The Miles-Ribner approach, which was developed in gas dynamics in the 1960 s, is used to describe Rossby waves interacting with the Gulf Stream and Kuroshio areas. The region of interaction is approximated by a nonzonal vortex layer. We apply the main formulations of the problem of a nonzonal vortex layer on the β-plane in the formulation of Miles-Ribner to observations in the real ocean. Earlier, we showed that the interaction of waves with a nonzonal flow gives rise to a new class of solutions, which is absent in the case of a zonal flow. This new class of solutions can be interpreted as the pure emission of Rossby waves by the nonzonal flow. We apply this theoretical approach to the areas of the Gulf Stream and Kuroshio as well. We use for analysis altimetry data available at Copernicus Marine Environment Monitoring Service. The analysis of Hovmöller diagrams in the areas under consideration confirms the previously obtained theoretical conclusions of the problem of the interaction of planetary waves with a nonzonal flow on the β-plane in the formulation of Miles-Ribner. The incident waves, as well as refracted and reflected waves are distinguished. The speed of refracted and reflected waves exceeds the speed of incident waves, which confirms the conclusions about the existence of mechanisms for the amplification of planetary waves when they interact with a nonzonal flow.  相似文献   

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