Near-equatorial and ground-based measurements of whistler-mode waves are accompanied by relativistic electron precipitation • In the presence (absence) of ducted wave propagation, as monitored by propagation to the ground, the precipitating electron energies are above (below) 150 keV • Ducted whistler-mode waves may play a key role in relativistic electron loss in the inner magnetosphere

High‐frequency heating of the ionosphere is effective for generating extremely low frequencies (ELF, 3–3000 Hz) through modulation of the auroral electrojet current. While the amplitudes of the resulting ELF waves depend on the auroral electrojet current strength, the polarization of their horizontal magnetic field remains relatively stable. In this work, we determined that at the distance of several wavelengths from an ionospheric ELF source created by two HF heating waves separated by an ELF frequency, polarization parameters are influenced by the Earth‐ionosphere waveguide. Previous experiments in the vicinity of the ionospheric ELF source have determined that the right‐hand polarization of the magnetic field measured at the ground typically prevails, whereas in this paper we demonstrate that at the distance of 660 km to the east of the European Incoherent Scatter, a circular left‐hand polarization dominates. We interpret this effect as a result of “trapping” of the left‐hand mode between the upper and lower boundaries of the Earth‐ionosphere waveguide, while the right‐hand or whistler mode leaks into the ionosphere.

The main feature of the magnetosphere consists in its filling with a large variety of waves at different frequency scales with different characteristics and of different origins. The natural electromagnetic waves at the audio range of frequencies (3-30 kHz) termed very low frequency (VLF) emissions are typical for the magnetospheric plasma as well. They are whistler mode waves of magnetospheric origin at the frequencies between the ion and electron gyrofrequency, that have propagated through the ionosphere to the ground.The natural VLF waves known as chorus, hiss, and quasiperiodic (QP) emissions have been widely studied more than 50 years since the classical monograph by Helliwell (1965). The majority of these emissions are usually generated at or near the geomagnetic equator in the magnetosphere through resonant cyclotron interactions with energetic (∼hundreds of keV) electrons of the Earth's radiation belts (e.g.

[1] Wavelet analysis has been performed on the low-frequency (0.1 to 16 Hz) electric and magnetic field variations observed by the low-altitude polar-orbiting Dynamic Explorer 2 (DE2) spacecraft. The application of the wavelet transform is conditioned by the fact that both magnetic and electric signals, as well as their ratio, vary along the spacecraft track. They grow from low values in the middle latitudes to the peak values in the center of the auroral zone and then subside in the transition to the polar cap. In such a case the wavelet transform technique appears most adequate for signal processing. Using the wavelet transform of the data, we compute the local intermittency measure and flatness of electric and magnetic fluctuations and demonstrate that both in the auroral zone and in the polar cap they are a manifestation of intermittent turbulence. In order to distinguish between the static and wave interpretations of the turbulent fields, the ratios of magnetic to electric field strengths are computed from wavelet magnitudes. Within the static interpretation, these ratios should be determined by the height-integrated ionospheric Pedersen conductivity, while in the wave interpretation they should be governed by the inverse impedance of Alfvén waves. It is shown that in the auroral zone, the observed magnetic to electric field ratios are in a better agreement with the values of Pedersen conductance (S P $ 5-10 mhos). This suggests that the fluctuations predominantly result from spacecraft crossing quasi-static field structures, which signatures are Doppler shifted when detected in the spacecraft frame.