Whistler propagation in inhomogeneous plasma

Abstract

[1] We present a numerical study of the propagation of VLF whistler waves in the magnetospheric plasma. In this study the plasma is considered to be homogeneous in the direction along the ambient magnetic field and strongly inhomogeneous across it. The goal of this investigation is to understand whistler propagation in magnetic-field-aligned channels (also called ducts) with either enhanced or depleted plasma density. In particular, the paper is focused on situations where the transverse scale size of the duct is comparable to or smaller than the perpendicular wavelength of the whistler. In this case, classical analysis of the whistler dynamics based on the geometrical optic approximation becomes invalid, and numerical solutions of the full wave equations should be performed. Our simulations extend the earlier analysis based on the ray-tracing technique and analytical studies of the very low frequency wave equations. We show that high-density ducts are inherently leaky and this leakage depends on the perpendicular wavelength of the wave inside the duct. We also show that whistler trapping occurs not only at density maxima and minima but also at critical points along a density gradient. This effect can explain whistler guiding along strong transverse plasma density gradients at the plasmapause.

Whistler propagation in ionospheric density ducts: Simulations and DEMETER observations

“…Even with this effective finite perpendicular wavelength, we expect these whistlers to be effectively trapped inside any of the three density enhancements [Streltsov et al, 2006]. Note that along with a finite perpendicular wavelength, both˙k ?…”

“…The basic theory of whistler ducting [Streltsov et al, 2006] tells us that a single duct is capable of trapping whistlers with particular a range of different wave normal angles. Based on the criteria of n > n 0 and the dispersion relationship, the maximum wave normal angle of a wave that can be trapped in a given density enhancement is max = cos…”

“…[12] It is sometimes convenient to instead use a flatbottomed channel model, particularly in theoretical studies [Streltsov et al, 2006], but some manner of bell-shaped profile (whether quadratic, Gaussian, or some other similarly behaved function) is typically assumed. Although any sort of profile is possible owing to the poor mobility of electrons across the magnetic field (they are "frozen-in" to the plasma at the frequencies of interest), it would be expected that the profile of the enhancement be similar to that of its source.…”

A simulation study of the propagation of whistler-mode chorus in the Earth’s inner magnetosphere

“…Numerical experiments are also useful, even though an amount of computational resources are required in solving a set of Maxwell's equations and the equation of motion of cold plasma, because they can reproduce the wave amplitude variation and the spatial extent of wave packets during their propagation (Streltsov et al 2006(Streltsov et al , 2010(Streltsov et al , 2012. In the present study, we have developed a spatially twodimensional simulation code for the study of the propagation of chorus in the dipole magnetic field.…”

Whistler waves with angular momentum in space and laboratory plasmas and their counterparts in free space

“…Eigenmodes are formed by integer azimuthal wavenumbers m and radially quantized wavenumbers k r = m/r due to reflecting boundaries. This concept has also been used in solid-state plasmas [8] and space plasmas for wave propagation in narrow density ducts [117]. This wave theory is questionable since in an anisotropic plasma the group and phase velocities differ, which yields different reflections for phase and group velocities.…”