Plasma waves near the Earth's bow shock and in the distant magnetotail

This dissertation uses recent WIND and GEOTAIL spacecraft measurements to examine plasma wave processes observed in the terrestrial electron foreshock, bow shock, distant tail slow shocks and lobes.; Electrostatic waves in the bow shock, distant tail slow shocks and lobes are investigated through fine scale structures in electron velocity distributions. With these structures at a parallel velocity below the electron thermal speed and near zero parallel velocity, the modes account for the narrowband midfrequency and the broadband high frequency waves detected. The simulation results do not suggest strong nonlinear behavior of the electrostatic waves in these regions.; A dispersion and 2-D electromagnetic particle-in-cell simulation study of the electron foreshock waves is conducted in a generalized Lorentzian plasma. With foreshock nonthermal electrons and moderate beam parameters, the nonlinear wave-wave interactions are found to be too weak to produce either the observed electromagnetic emissions at the fundamental of the plasma frequency or the backward-propagating Langmuir waves required to generate the second harmonic electromagnetic waves.; To explain the foreshock electromagnetic emissions, linear mode conversion from high frequency electrostatic to electromagnetic waves for a weakly magnetized warm plasma with a longitudinal linear density profile is investigated analytically. The study examines the transition from an unmagnetized to a magnetized plasma in the formulation of governing equations, the mode structure, and solutions. A set of four coupled differential equations derived using a fluid treatment describes the coupling of the Langmuir wave, the upper-hybrid wave, the O, X, and Z modes. The coupled equations are solved near the conversion region, and the reflection and conversion coefficients are obtained. It is found that the magnetic field narrows the window of conversion and reduces the angle of electromagnetic wave propagation with respect to the magnetic field. Results indicate that linear conversion in an inhomogeneous plasma could provide a plausible explanation for the foreshock first harmonic electromagnetic emissions and the backward-propagating Langmuir waves required for the generation of the second harmonic electromagnetic waves.