Abstract
Nonthermal continuum (NTC) electromagnetic radiation is generated within the Earth's magnetosphere and radiated to the outer space. We present cases of a specific type of NTC, which appears as multiple wide bands on the spectrograms recorded by the Cluster spacecraft just outside the plasmapause. This NTC comes from several sources located in the plasmapause density gradient where the local upper hybrid frequency is close to the harmonics of the electron cyclotron frequency. Analysis of one of these events at the eighth harmonic frequency indicates that, in the vicinity of the source, the electric field fluctuations are polarized in the plane perpendicular to the magnetic field line. Hot‐plasma dispersion relation based on the measured electron distribution shows that the observed polarization excludes the presence the Langmuir mode and the ordinary mode. This analysis suggests that the observed waves can propagate in the L mode or, for perpendicular wave vectors, in the extraordinary Z mode or on a complex structure of hot‐plasma Bernstein modes coupled to the Z mode at the upper hybrid frequency.
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