The propagation of whistler waves in a magnetized plasma containing multiple small-scale (100 m to 1 km) field-aligned irregularities of enhanced electron density is considered analytically and by means of numerical simulations. Such systems of irregularities can develop in the upper ionosphere during the generation of density ducts by high-frequency heating facilities and other types of active experiments. The simulation parameters are close to those of an active experiment where a whistler wave of 18 kHz emitted by a ground-based very low frequency (VLF) transmitter was received onboard the DEMETER satellite at 700 km above the SURA heater. The study reveals a number of remarkable properties of the VLF waves' propagation, including the existence of specific waveguide modes of the small-scale density structures and of a characteristic transverse size d 0 of the irregularities. Irregularities with small density enhancements around 10-20% and transverse sizes larger than d 0 ∼ 1 km can serve as separate waveguides for VLF waves. In their turn, single irregularities narrower than d 0 cannot be considered as individual ducting structures. Numerical simulations show that, for the analysis of the electromagnetic whistlers' propagation, a system of closely spaced irregularities with scales narrower than d 0 can be modeled by an equivalent ducting structure with a smoothed density profile. Such equivalent structure has the same ducting properties for whistlers and can be produced by averaging with a sliding window of a scale about d 0 the original density distribution.

Effects of lightning‐induced generation of high‐frequency and microwave radiation are of great interest for studying fundamental physics of lightning and its applications for monitoring of the thunderstorm activity and protection of equipment against electromagnetic interference. Ultrawideband electromagnetic pulses (UWB EMPs) of spark discharges about 1 m long were detected in a frequency band of up to 10 GHz in laboratory experiments using a cloud of water droplets charged up to the electric potential exceeding 1 MV. Electromagnetic pulses with characteristic front buildup durations from 50  to 100 ps were produced by streamer flashes, at the stage of leader propagation and the main stage of the discharge (i.e., the return stroke). Electric and magnetic fields of pulses were measured, and the radiation polarization was determined. The UWB EMP waveforms and the spectra obtained experimentally are consistent with colliding streamer models.

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The properties of whistler waves propagating in a large laboratory magnetoplasma with magnetic field irregularities have been studied. Two types of ambient magnetic field inhomogeneities have been considered: (i) a localized “lenslike” perturbation and (ii) an elongated “ductlike” irregularity. The magnetic field was perturbed by immersing into the plasma, without creating any significant plasma density disturbances, additional current-carrying coils. It has been found that the presence of magnetic field irregularities causes the whistler wave’s diffraction and affects their patterns substantially. Plasma regions with locally enhanced magnetic field strength focus oblique whistlers; oppositely, local magnetic field minima debunch the whistler waves. In case of prolonged magnetic field irregularity formation—encompassing several whistler wavelengths along its size—the diffraction effects are distinctly pronounced; even the comparatively weak magnetic field disturbances at the level of 10% lead to strong modifications of the whistler waves’ pattern. Theoretical calculations are presented which confirm the related experimental measurements. The obtained results are of great importance for laboratory plasmas as well as magnetospheric physics, and represent a new look at the problem of whistler waves’ scattering and ducting, caused not by the plasma density ducts and gradients, but by magnetic field irregularities.