Cyclotron-resonance amplification of VLF and ULF whistlers

Abstract

Electromagnetic signals that propagate through the magnetosphere exchange energy with nonthermal charged particles by the cyclotron‐resonance mechanism. The interaction is due to a Doppler shift of the propagation frequency ω to the cyclotron frequency ωc of the charged particle that allows the particle to resonate with the electromagnetic fields. The dominant exchange is between electrons around 1 kev and VLF whistlers that propagate in the right‐hand mode and between protons around 1 kev and ULF whistlers (Pc 1 geomagnetic micropulsations) that propagate in the left‐hand mode. The complex wave number k(ω) = kr + iki for propagation in a hot uniform plasma parallel to a static magnetic field is assumed to describe whistler properties locally in the magnetosphere. The power transfer function A(ω), which relates the input and output power spectrums, is determined by the path integral of ki along a geomagnetic flux tube. Spectrums of A for both VLF and ULF whistlers have been evaluated for a variety of energy and pitch‐angle distributions of the form E−n sinm α. In general, A has an amplification maximum just below a sharp absorption cutoff, which is consistent with observations. The detailed input‐output spectrums of whistlers that are necessary to test the theory are not available yet. When these spectrums are measured, this interaction may provide a possible method for mapping the phase space distribution of nonthermal particles in the magnetosphere.

Substorm aspects of magnetic pulsations

“…The effects which are produced by a small perpendicular velocity were soon studied (Bell and Buneman, 1964;Gendrin, 1965;Trakhtengertz, 1967). Rapidly it became obvious that one should not consider quasimonocinetic beams, or 'bumps' in the particle velocity distribution function, but that all the energetic particles were contributing to the wave amplification factor (Cornwall, 1966;Kennel and Petschek, 1966;Liemohn, 1967).…”

“…The higher the frequency considered, the higher should be the anisotropy factor of the energetic particles in order to overcome this damping. The conditions which are to be fulfilled by the anisotropic coefficient in order to get amplification in different cases are summarized in Table III*, which is deduced from the work of Liemohn (1967). In the case of interactions with TABLE III Possibility of amplification for different anisotropy factors and different types of interaction.…”

Parameterization of Ring Current Adiabatic Energization

“…Another is the excitation of plasma waves. With the hot electrons, whistler waves are excited, resulting in plasmaspheric hiss [Liemohn, 1967;Church and Thorne, 1983], which can scatter the hot electrons [Dungey, 1963;Liemohn et al, 1997] and ions [Kozyra et al, 1995]. With the hot ions, electromagnetic ion cyclotron waves are excited [e.g., Kennel and Petschek, 1966;Khazanov et al, , 2003b, which can interact with (i.e., scatter) the hot ions [Jordanova et al, 1997;Khazanov et al, , 2003b and electrons [Summers and Thorne, 2003].…”

Elf Propagation and Emission in the Magnetosphere

“…Details of the mechanism are given in the section on propagation theory; only its application to individual ULF whistlers is described here (34,37,39,91,92). …”

“…FiTUR-E RFSEARCH 26 Cyclotron-re-onance amplification of hydromagnetic wave packets propagating along field-line paths for specific energy (E) and pitch angle (a) distributions of ions (34). Global distribution of rapid-run geomagnetic (bserva-39 tories.…”