Pulsations are studied with in situ observations in space of both magnetic and electric fields, and with ground-based magnetometers . In order to study the generation mechanisms of these waves, several points should be studied, including frequency characteristics, incl. Pc 1-2 pulsations are locally generated at equatorial magnetosphere by EMIC instability. At lower frequencies continuous pulsations sharing the same frequency range may differ, e.g., in their polarization, harmonic structure, or occurrence region, and have thus different origin.
Latter type relate to resonances of field lines and magnetospheric cavity .
Incoherent noise everywhere unknown increases with magnetic activity For upstream generated waves, one important task is to establish linkage between waves external and internal to the magnetosphere. The question is, what are the sites of transfer of external to internal wave energy. Note that actually all pulsations, ultimately, derive their energy from the solar wind. This is because the particles taking part in the local instabilities are energized via the convection electric field imposed by the solar wind. Similarly the precipitating particles and impinging electric field in the ionosphere are solar wind powered.