Whistler interactions with density gradients in the magnetosphere

Naturally occurring density variations of a few to tens of percent from the background are a ubiquitous feature of the magnetospheric plasma. Very-low frequency (VLF) whistler mode waves (whistlers), which have wavelengths in the middle of this range, are particularly affected by the presence of these density variations. At sub-wavelength scales, these variations are responsible for localized enhancements of wave magnetic and/or electric fields and mode conversion to electrostatic lower hybrid waves. At scales much larger than the wavelength, these variations can be responsible for guiding whistlers along the ambient magnetic field. Recently, large-amplitude whistlers have been observed in the Earth's radiation belts. Unlike the more frequently observed whistler-mode chorus, which propagates primarily parallel to the background magnetic field, these waves were found to propagate at highly oblique angles.