Case studies on the wave propagation and polarization of ELF emissions observed by Freja around the local proton gyrofrequency

Using a multicomponent measurement of electric and magnetic fields in the E LF range, we investigate the polarization and propagation characteristics o f several types of electromagnetic emissions around the local proton gyrofr equency. The data of the low-orbiting Freja satellite are examined in the a uroral and subauroral regions as well as inside the plasmasphere. We confir m previous results on the properties of the high-latitude hiss with a sharp lower cutoff just below the local proton gyrofrequency. The waves propagat e downward from higher altitudes outside the plasmasphere and reflect at th e local two-ion cutoff frequency. With an enhanced data representation we a re able to characterize the reflected upgoing waves on both poleward and eq uatorward edges of the hiss emission. The high-latitude emissions in a larg e band below the local proton gyrofrequency contain right-hand circularly p olarized waves propagating nearly parallel to the terrestrial magnetic fiel d. We believe these emissions can originate by tunnelling of the right-hand -polarized hiss below the two-ion crossover frequency. We report high-latit ude "frequency drift phenomena" below the local proton gyrofrequency. The f requency of these faint emissions increases by several tens of hertz per la titude degree. The electromagnetic noise at low frequencies is always found with a high degree of a nearly linear polarization. Upgoing ion whistlers are observed to follow each other with time delays as low as about 100 ms.