Finite Larmor Radius effect and nonlinear oscillations in magnetosphere (original) (raw)
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Electron acoustic nonlinear structures in planetary magnetospheres
Physics of Plasmas, 2018
In this paper, we have studied linear and nonlinear propagation of electron acoustic waves (EAWs) comprising cold and hot populations in which the ions form the neutralizing background. The hot electrons have been assumed to follow the generalized ðr; qÞ distribution which has the advantage that it mimics most of the distribution functions observed in space plasmas. Interestingly, it has been found that unlike Maxwellian and kappa distributions, the electron acoustic waves admit not only rarefactive structures but also allow the formation of compressive solitary structures for generalized ðr; qÞ distribution. It has been found that the flatness parameter r, tail parameter q, and the nonlinear propagation velocity u affect the propagation characteristics of nonlinear EAWs. Using the plasmas parameters, typically found in Saturn's magnetosphere and the Earth's auroral region, where two populations of electrons and electron acoustic solitary waves (EASWs) have been observed, we have given an estimate of the scale lengths over which these nonlinear waves are expected to form and how the size of these structures would vary with the change in the shape of the distribution function and with the change of the plasma parameters.
The propagation of electron acoustic solitary waves is investigated in magnetized two-temperature electron plasma with supra-thermal ion. By using the reductive perturbation technique, the Korteweg de-Vries (KdV) equation is derived. Later solving this equation, a solitary wave solution has been derived. These are mainly in astrophysical plasmas where changes of local charge density, temperature, and energy of particles produce considerable effects on the plasma system. The effects of supra-thermality, density, and Mach number on solitary structures are studied in detail. The results show that the supra-thermal index () and ion to electron temperature ratio () alters the regime where solitary waves may exist. While studying the solitary profile for different parametric variation some interesting conclusion can be drawn; it is shown that the solitary profile becomes flatter. This can be due to the thermal energy associated with the hot electrons. However, with the increase in ion density with respect to the cold electrons' density, the solitary waves become steeper and sharper. This is due to the comparatively heavier mass of ions. The density of cold electron also increases the solitary structures in a similar manner. The higher the density of cold electrons, sharper will be the profile. The above findings will be helpful in understanding many astrophysical phenomena and data obtained by space missions. For a further study, we keep the investigation of the formation of other kinds of stationary structures like shocks, double layers, etc.
Non-linear high-frequency waves in the magnetosphere
Pramana, 2003
Using fluid theory, a set of equations is derived for non-linear high-frequency waves propagating oblique to an external magnetic field in a three-component plasma consisting of hot electrons, cold electrons and cold ions. For parameters typical of the Earth's magnetosphere, numerical solutions of the governing equations yield sinusoidal, sawtooth or bipolar wave-forms for the electric field.
Astrophysics and Space Sciences Transactions, 2007
Necessary conditions are discussed for the possible generation of large solitary acoustic modes in plasmas with one or more ion species which are hotter than some or all of the electron species. The analysis is based on a fluid dynamic approach. It is found that in most of these configurations the existence ranges for the solitary wave velocities are very narrow and close to one of the thermal velocities. In the latter situation, linear Landau damping may prevent the generation of nonlinear structures. The analysis indicates that both inertial and thermal effects for the ions need to be kept in the description, thus rendering an analytical investigation much more intricate.
Electron acoustic solitary waves in the Earth’s magnetotail region
Advances in Space Research, 2009
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.
Nonlinear ion acoustic wave in a pair-ion plasma in a uniform weak magnetic field
Physica Scripta, 2015
The dynamics of the nonlinear ion acoustic waves are investigated in the presence of an external weak magnetic field in pair-ion plasma in which the mass (temperature) of the positive ions are smaller (larger) than that of the negative ions. The linear dispersion relation of the ion acoustic wave is found to be modified by the externally applied magnetic field. The standard perturbative approach leads to a modified form of Korteweg-de Vries equation. The analytical as well as numerical solutions reveal that the localized (solitary wave) solutions decay slowly algebraically due to the Lorentz force by radiating energy to the tails of the dispersive ion acoustic waves. The results are discussed in the context of the lower region of D-layer ionospheric plasma.
Physica Scripta, 2022
Motivated by the recent Magnetospheric Multiscale (MMS) observations of oblique electron acoustic waves, we addressed the generation mechanism of the observed waves by utilizing the reductive perturbation technique. The nonlinear Zakharov-Kuznetsov (ZK) equation is derived for collisionless, magnetised plasma composed of cool inertial background electrons, the cool inertial electron beam, hot inertialess suprathermal electrons represented by a κ-distribution, and stationary ions. Moreover, the instability growth rate is derived by using the small-k perturbation expansion method. Our findings reveal that the structure of the electrostatic wave profile is significantly influenced by the external magnetic field, the unperturbed hot, cool, and electron beam densities, the obliquity angle, and the rate of superthermality. Such parameters also affect the instability growth rate. This study clarifies the characteristics of the oblique electron solitary waves that may be responsible for changing the electron and ion distribution functions, which alter the magnetic reconnection process. Moreover, increasing the growth rate with the plasma parameters could be a source of anomalous resistivity that enhances the rate of magnetic reconnection.
Nonlinear Interaction of Acoustic Waves With Plasma of the Ionosphere: Theory and Experiment
This report is devoted to the experimental and theoretical aspects of the nonlinear interaction and influence of the acoustic waves on the ionosphere. This nonlinear phenomenon gives the possibility to simulate the acoustic channel of the lithosphere-atmosphere-ionosphere connection, and to investigate experimentally this channel by means of acoustic generators located on the earth surface. The increase of the transparency of the ionosphere for the cosmic radiowaves caused by a low frequency atmospheric acoustic wave is investigated. Atmospheric acoustic wave creates in the ionosphere a periodic structure of the electron density, like the one created by using two high-power radiowave signals. It is shown that if the length of the acoustic wave is equal or larger than the radiowave length, then a resonant transmission of the radiowaves takes place in the ionosphere.
Small amplitude nonlinear electron acoustic solitary waves in weakly magnetized plasma
Physics of Plasmas, 2013
Nonlinear electron acoustic waves are studied in a quasineutral plasma in the presence of a variable magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary positively charged ion background. Linear analysis of the governing equations manifests dispersion relation of electron magneto sonic wave. Whereas, nonlinear wave dynamics is being investigated by introducing Lagrangian variable method in long wavelength limit. It is shown from finite amplitude analysis that the nonlinear wave characteristics are well depicted by KdV equation. The wave dispersion arising in quasineutral plasma is induced by transverse magnetic field component. The results are discussed in the context of plasma of Earth's magnetosphere. V C 2013 AIP Publishing LLC. [http://dx.
Journal of Geophysical Research: Space Physics, 2015
The mutual nonlinear interplay of kinetic Alfvén wave (KAW) and ion acoustic wave, for the high-β plasma (i.e., m e /m i ≪ β ≪ 1, where β is thermal to magnetic pressure ratio) in the magnetopause, has been considered in the present study. A set of dimensionless nonlinear Schrödinger equations has been derived taking into account the finite frequency as well as ion temperature corrections. The dynamical equation of the ion acoustic wave (propagating at an angle with respect to the background magnetic field) in the presence of ponderomotive nonlinearity due to KAW is also derived. Numerical simulation has been carried out to study the effect of nonlinear interaction between these waves which results in the formation of localized structures and turbulent spectrum, applicable to the high-β plasmas like magnetopause regions. Results reveal that due to the nonlinear interplay between these waves, natures of the formation of localized structures are complex and intense in nature in quasi steady state. From the results, we have found that spectral index follows the scaling ∼k À 3=2 ⊥ at large scale and spectral index follows ∼k À 2:80 ⊥ À Á at small scale. We also found the steepening in the turbulent spectrum. Steepening in the turbulence spectrum has been reported by the Time History of Events and Macroscale Interactions during Substorms spacecraft across the magnetopause, and results are found to be consistent with spacecraft observation. RINAWA ET AL.