Listening in the Plasma Universe

Abstract:

Through waves we are perceive many phenomena of our immediate and distant environment. Without light waves we would not know about each other, without acoustic waves I could barely communicate with you. Waves as a means to communicate are most important, not only in daily life, but also in our understanding of nature. Geomagnetic pulsations told us and still tell us about dynamic processes in the magnetosphere. Their spatial and temporal characteristics bear information about the generation process as well as the medium permeated. Global occurrence statistics provide a means to map out the magnetosphere. Following the footsteps of astronomers, searching the sky in the infra-red, visible, or ultra-violet range, we are listening in the plasma universe using low-frequency waves. Drivers of these waves are electric currents, caused by a plethora of plasma instabilities, indicating non-thermal phase space distributions, non-uniform plasma conditions, or moving bodies of different kinds. Accumulating knowledge of these processes allows us to disentangle the special wave characters observed. Our beloved pulsations, generated by oscillating currents in the ionosphere, may be stripped like an onion. Deconvolution from the ionosphere through the plasmasphere and outer magnetosphere up into the solar wind now is possible. Ground-based observations become monitors for the conditions in the outer magnetosphere and the solar wind. Waves tell us about their “communication” with charged particles, their acceleration, and other conversions of electro-magnetic into kinetic energy and vice versa. All of these processes we have not yet understood. But travelling in space, to other planetary bodies, or our Sun, offers us adventures in parameter space. Different background plasma conditions, various geometries, rotational effects, the diverse conditions met out there convert us from passive observers into active experimenters. Plasma waves are not just little wiggles, waves matter!