Anomalous width variation of rarefactive ion acoustic solitary waves in the context of auroral plasmas

The presence of dynamic, large amplitude solitary waves in the auroral regions of space is well known. Since their velocities are of the order of the ion acoustic speed, they may well be considered as being generated from the nonlinear evolution of ion acoustic waves. However, they do not show the expected width-amplitude correlation for K-dV solitons. Recent POLAR observations have actually revealed that the low altitude rarefactive ion acoustic solitary waves are associated with an increase in the width with increasing amplitude. This indicates that a weakly nonlinear theory is not appropriate to describe the solitary structures in the auroral regions. In the present work, a fully nonlinear analysis based on Sagdeev pseudopotential technique has been adopted for both parallel and oblique propagation of rarefactive solitary waves in a two electron temperature multi-ion plasma. The large amplitude solutions have consistently shown an increase in the width with increasing amplitude. The width-amplitude variation profile of obliquely propagating rarefactive solitary waves in a magnetized plasma have been compared with the recent POLAR observations. The width-amplitude variation pattern is found to fit well with the analytical results. It indicates that a fully nonlinear theory of ion acoustic solitary waves may well explain the observed anomalous width variations of large amplitude structures in the auroral region

Study of solitary waves in space plasmas

Theoretical investigations have been made of arbitrary amplitude electrostatic solitary waves in non-thermal plasmas, which may be of relevance to ionospheric and magnetospheric plasmas, and dusty plasmas, which are most common in earth's and cometary environments as well as in planetary rings, for understanding the nonlinear features of localised electrostatic disturbances in such space plasma systems. This thesis starts with an introductory chapter where a very brief historical review of solitary waves in plasmas has been presented. The study of arbitrary amplitude electrostatic solitary waves in non-thermal plasma has considered a plasma system consisting of warm adiabatic ions and non- thermal electrons. It is found that a non-thermal electron distribution may change the nature of ion-acoustic solitary waves. If the ions are assumed to respond as a fluid to perturbations in the potential, with no significant trapping in a potential well, then a thermal plasma only supports solitary waves with a density peak. However, with a suitable distribution of non-thermal electrons, solitary waves with both density peaks and density depressions may exist. This study has also included a numerical analysis showing how these electrostatic solitary structures evolve with time. The investigation has then been extended to magnetised plasmas to study the effects of magnetic field on obliquely propagating electrostatic solitary structures. This attempt first employed the reductive perturbation method and investigated the nonlinear properties of small but finite amplitude obliquely propagating solitary waves in this magnetised non-thermal plasma model. This study is then generalised to arbitrary amplitude solitary waves by the numerical solution of the full nonlinear system of equations. This numerical method has also been utilised to present a similar study in another popular plasma model, namely the two-electron-temperature plasma model. The study of arbitrary amplitude solitary waves in a dusty plasma has considered another plasma system which consists of an inertial dust fluid and ions with Maxwellian distribution and has investigated the nonlinear properties of dust- acoustic solitary waves. A numerical study has also been made to show how these dust-acoustic solitary waves evolve with time. The effects of non-thermal and vortex-like ion distributions are then incorporated into this study. The study of arbitrary amplitude electrostatic solitary waves in this thesis has finally been concluded with some brief discussion of our results and proposal for further studies, which are expected to generalise and develop our present work to some other extents, in this versatile area of research

Linear and nonlinear fluctuations in multicomponent plasmas applied to magnetospheric environments.

Doctor of Philosophy in Chemistry. University of KwaZulu-Natal, Durban 2015.In this thesis, we discussed the linear and nonlinear effects in multicomponent plasmas. By multicomponent, we refer to electron-positron-ion and electron-positron-dust type plasmas. The linear electrostatic waves in magnetized three-component electron-positron-ion plasmas consisting of cool ions, and hot Boltzmann electrons and positrons have been investigated in the low-frequency limit. By using the continuity and momentum equations with the Poisson equation, the dispersion relation is derived. Two stable modes of the waves are investigated in different cases, viz parallel and perpendicular propagation. The effects of the density and the temperature ratio on the wave structures are investigated. We also studied the behavior of the nonlinear electrostatic waves: first, we consider the electrons and positrons as having Boltzmann density distributions and the ions being governed by the fluid equations, and second we extend our model by assuming that all species are governed by the fluid equations. The set of nonlinear differential equations is obtained and this set is numerically solved for the electric field. The numerical solutions exhibit the range of period varying from sinusoidal to sawtooth to spiky waveforms. The effects of the driving electric field, temperature, concentration, drift velocity, Mach number and propagation angle on the wave structures are investigated. Finally, the study ends by investigating solitary waves in an electron-positron-dust plasma. The arbitrary amplitude dust acoustic solitary waves has been studied by using Sagdeev pseudopotential approach in a plasma consisting of hot electrons and positrons, and cold dust grains. The conditions of the existence of solitons are found assuming constant dust charge

Space Plasma Physics: A Review

Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to Earth’s ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally, high-technology ground-based instrumentation has led to new and greater knowledge of solar and auroral features. As a result, a new branch of space physics, i.e., space weather, has emerged since many of the space physics processes have a direct or indirect influence on humankind

Solar Terrestrial Physics: Present and Future

The following topics relating to solar-terrestrial interactions are considered: (1) reconnection of magnetic fields; (2) particle acceleration; (3) solar magnetic flux; (4) magnetohydrodynamic waves and turbulence in the Sun and interplanetary medium; (5) coupling of the solar wind to the magnetosphere; (6) coronal transients; (7) the connection between the magnetosphere and ionosphere; (8) substorms in the magnetosphere; (9) solar flares and the solar terrestrial environment; (10) shock waves in the solar terrestrial environment; (11) plasma transport and convection at high latitudes; and (12) high latitude ionospheric structure

Coronal Holes

Coronal holes are the darkest and least active regions of the Sun, as observed both on the solar disk and above the solar limb. Coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. This paper reviews measurements of the plasma properties in coronal holes and how these measurements are used to reveal details about the physical processes that heat the solar corona and accelerate the solar wind. It is still unknown to what extent the solar wind is fed by flux tubes that remain open (and are energized by footpoint-driven wave-like fluctuations), and to what extent much of the mass and energy is input intermittently from closed loops into the open-field regions. Evidence for both paradigms is summarized in this paper. Special emphasis is also given to spectroscopic and coronagraphic measurements that allow the highly dynamic non-equilibrium evolution of the plasma to be followed as the asymptotic conditions in interplanetary space are established in the extended corona. For example, the importance of kinetic plasma physics and turbulence in coronal holes has been affirmed by surprising measurements from UVCS that heavy ions are heated to hundreds of times the temperatures of protons and electrons. These observations point to specific kinds of collisionless Alfven wave damping (i.e., ion cyclotron resonance), but complete models do not yet exist. Despite our incomplete knowledge of the complex multi-scale plasma physics, however, much progress has been made toward the goal of understanding the mechanisms responsible for producing the observed properties of coronal holes.Comment: 61 pages, 12 figures. Accepted by the online journal "Living Reviews in Solar Physics." The abstract has been abbreviated slightly, and some figures are degraded in quality from the official version, which will be available at http://solarphysics.livingreviews.org

Space Technology Plasma Issues in 2001

The purpose of the workshop was to identify and discuss plasma issues that need to be resolved during the next 10 to 20 years (circa 2001) to facilitate the development of the advanced space technology that will be required 20 or 30 years into the future. The workshop consisted of 2 days of invited papers and 2 sessions of contributed poster papers. During the third day the meeting broke into 5 working groups, each of which held discussions and then reported back to the conference as a whole. The five panels were: Measurements Technology and Active Experiments Working Group; Advanced High-Voltage, High-Power and Energy-Storage Space Systems Working Group; Large Structures and Tethers Working Group; Plasma Interactions and Surface/Materials Effects Working Group; and Beam Plasmas, Electronic Propulsion and Active Experiments Using Beams Working Group