This paper presents results from a modeling study of localized packages of very low frequency (VLF) whistler mode waves observed by the NASA Van Allen Probes (also known as the Radiation Belt Storm Probes [RBSP]) satellites in the equatorial magnetosphere. The waves are detected inside enhancements of the plasma density, which we interpret as high‐density ducts. The quality of the ducting depends on the wave and duct parameters. The goal of this study is to investigate relations between these parameters. This study is based on the analysis and simulations of the electron MHD model. The results demonstrate that (1) the high‐density ducts with the magnitudes and perpendicular sizes observed by the RBSP satellites can trap VLF waves with the observed frequency and guide them over a significant distance with little attenuation. (2) It is possible to identify the range of magnitudes of the parallel and perpendicular wavelengths using the information about frequency of the waves and parameters of the duct.

Ultra low frequency (ULF) electromagnetic waves have been regularly observed by the CRRES, Cluster, and Van Allen Probes satellites near the plasmapause during substorms. Frequently, the small‐scale waves are detected together with a large‐scale quasi‐stationary electric field collocating with mesoscale plasma flows penetrating into the plasmasphere. These observations suggest that the plasmapause plays an important role in the conversion of the kinetic energy of energetic particles moving toward the Earth from the reconnection site in the magnetotail into a large‐scale electric field. The field penetrates along the magnetic field into the ionosphere and generates small‐scale, shear Alfvén waves and field‐aligned currents. These waves can form a standing pattern between the hemispheres, and under certain conditions, they can be amplified by interactions with the ionosphere. This scenario is verified in the paper by reproducing with simulations structure and amplitude of the ULF waves observed by the Van Allen Probe‐A satellite near the plasmapause on 17 March 2015. The simulations are based on the reduced two‐fluid MHD model describing generation of ULF Alfvén waves and field‐aligned currents by the ionospheric feedback instability driven by the large‐scale electric field. Simulations demonstrate good, quantitative agreement between spatial structure, frequency, and amplitude of the simulated waves and the observations.

The ionospheric feedback instability (IFI) has been considered one of the main generation mechanisms for large‐amplitude ultra‐low frequency (ULF) waves and small‐scale field‐aligned currents in the auroral and subauroral regions for more than 40 years. Sydorenko and Rankin[2017] (SR17, hereafter) have recently challenged the very existence of the IFI for any realistic geophysical conditions in the Earth's ionosphere‐magnetosphere system. Because this conclusion contradicts numerous theoretical, numerical and experimental works successfully used IFI to explain and predict results from observations for more than four decades, it deserves special attention. We show that this conclusion is mainly based on the specific ionospheric density profile and boundary conditions used in two runs of simulations presented in SR17, and the generalization of this result is not justified. The effect of the collisions between ionospheric ions and neutrals on the development of the instability has been well studied since 1981, and these studies demonstrate that it does not prevent the development of the instability. Furthermore, excellent agreement of the theoretical and numerical results with observations verify without doubt the IFI existence and significance in the Earth's magnetosphere‐ionosphere system.