ABSTRACT
Finite plasma temperatures are most important for electrostatic waves, which are generally those with the smallest phase velocities. Heuristically, the authors might argue that thermal effects are of minor importance when a wave propagates at a velocity much larger than the thermal speed. Langmuir waves can be generated in the Earth’s near space plasma environment. In local thermal equilibrium, low level plasma waves can be thermally excited as described by the fluctuation-dissipation theorem. The electron plasma frequency can then be estimated to good accuracy. Thereby also the local plasma density in the ionosphere can be obtained by remote techniques, i.e., as an alternative to in situ rocket or satellite observations. The concept of Cerenkov radiation is assumed to be well known; when a particle happens to move with a velocity exceeding the speed of light in the actual medium.
