The paper discusses the excitation of monochromatic ELF/VLF electromagnetic waves produced by HF heating facility currents in the nighttime ionosphere. The ground-based magnetic field is predominantly located under the source, and the wave has right-hand polarization typical for a whistler but left-hand polarization at large distances from the source. About half of the source energy propagates upward, and approximately 20 % propagates to the Earth–ionosphere waveguide.

The paper discusses a problem concerned with the excitation of chorus with small wave normal angles along the external magnetic field in the magnetosphere. We examine the realisation of the beam pulse amplifier mechanism of chorus excitation without strong anisotropy of the plasma particle distribution function in the density ducts with refractive reflection. It is shown that in the ducts, discrete spectral elements of chorus can be excited at close to half of the electron cyclotron frequency.

A VLF chorus is a very intense electromagnetic plasma wave that is naturally excited as a succession of discrete emissions near the magnetic equatorial plane outside the plasmasphere. We introduce a mechanism of chorus excitation under conditions when known mechanisms become ineffective. This kind of excitation is related to the amplification of short electromagnetic pulses from the noise level even in a stable plasma. Obtained results can explain some important features of the chorus emissions.

We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusually high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). In one event, the spectral–temporal forms of the emissions looked like a series of giant bullets, with very abrupt cessation. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations.

The problems of reflection and transmission of a whistler wave incident in the nighttime ionosphere from above are considered. Numerical solutions of the wave equations for a typical condition of the lower ionosphere are found. The energy reflection coefficient and horizontal wave magnetic field on the ground surface are calculated. The obtained results are important for analysis of the ELF–VLF emission phenomena observed from both the satellites and the ground-based observatories.