Whistler

About: Whistler is a research topic. Over the lifetime, 3766 publications have been published within this topic receiving 91363 citations.

Geospace Environmental Modeling (GEM) magnetic reconnection challenge

Abstract: The Geospace Environmental Modeling (GEM) Reconnection Challenge project is presented and the important results, which are presented in a series of companion papers, are summarized. Magnetic reconnection is studied in a simple Harris sheet configuration with a specified set of initial conditions, including a finite amplitude, magnetic island perturbation to trigger the dynamics. The evolution of the system is explored with a broad variety of codes, ranging from fully electromagnetic particle in cell (PIC) codes to conventional resistive magnetohydrodynamic (MHD) codes, and the results are compared. The goal is to identify the essential physics which is required to model collisionless magnetic reconnection. All models that include the Hall effect in the generalized Ohm's law produce essentially indistinguishable rates of reconnection, corresponding to nearly Alfvenic inflow velocities. Thus the rate of reconnection is insensitive to the specific mechanism which breaks the frozen-in condition, whether resistivity, electron inertia, or electron thermal motion. The reconnection rate in the conventional resistive MHD model, in contrast, is dramatically smaller unless a large localized or current dependent resistivity is used. The Hall term brings the dynamics of whistler waves into the system. The quadratic dispersion property of whistlers (higher phase speed at smaller spatial scales) is the key to understanding these results. The implications of these results for trying to model the global dynamics of the magnetosphere are discussed.

Relativistic theory of wave‐particle resonant diffusion with application to electron acceleration in the magnetosphere

Abstract: Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented, for plasma parameters representative of the Earth's magnetosphere at locations both inside and outside the plasmapause. The results obtained indicate minimal electron energy change along the diffusion curves for resonant interaction with L mode waves. Intense storm time EMIC waves are therefore ineffective for electron stochastic acceleration, although these waves could induce rapid pitch angle scattering for ≳ 1 MeV electrons near the duskside plasmapause. In contrast, significant energy change can occur along the diffusion curves for interaction between resonant electrons and whistler (R mode) waves. The energy change is most pronounced in regions of low plasma density. This suggests that whistler mode waves could provide a viable mechanism for electron acceleration from energies near 100 keV to above 1 MeV in the region outside the plasmapause during the recovery phase of geomagnetic storms. A model is proposed to account for the observed variations in the flux and pitch angle distribution of relativistic electrons during geomagnetic storms by combining pitch angle scattering by intense EMIC waves and energy diffusion during cyclotron resonant interaction with whistler mode chorus outside the plasmasphere.

An ISEE/Whistler model of equatorial electron density in the magnetosphere

Abstract: Attention is given to an empirical model of equatorial electron density in the magnetosphere covering the L range 2.25-8. Although the model is primarily intended for application to the local time interval 00-15 MLT, a way to extend the model to the 15-24-MLT period is presented. The model describes, in piecewise fashion, the 'saturated' plasmasphere, the region of steep plasmapause gradients, and the plasma trough. Within the plasmasphere the model profile can be expressed as logne - Sigma-xi, where x1 = -0.3145L + 3.9043 is the principal or 'reference' term, and additional terms account for: a solar cycle variation with a peak at solar maximum; an annual variation with a December maximum; and a semiannual variation with equinoctial maxima.

An investigation of whistling atmospherics

Abstract: The paper, which is in two parts, describes an investigation of the nature and origin of the 'whistling atmospherics' or 'whistlers' which are sometimes observed at frequencies below 15 kc/s. The first part describes an experimental study of their properties, in the course of which a considerable number of whistlers were recorded and analyzed, and the law of the variation of their frequency with time determined. Some whistlers are heard to follow impulsive atmospherics, and these are found to be produced in the normal way by lightning strokes taking place within a distance of about 2000 km. Other whistlers are unaccompanied by atmospherics; they differ from the former type in several further respects. The diurnal and annual variations of the properties of both types of whistler have also been studied. In the second part of the paper a theory of the origin of the whistling atmospherics, originally due to Barkhausen (1930) and Eckersley (1935), is developed in detail. The theory proposes that they are due to waves which originate in normal impulsive atmospherics and travel through the outer ionosphere, following the lines of force of the earth's magnetic field and crossing over the equator at a great height. During their journey they become dispersed so as to arrive as 'whistlers'. They may be reflected from the earth's surface back along the same path, one or more times, to produce whistlers with increased dispersions. The effects responsible for the guiding of the waves along the lines of the geomagnetic field provide sufficient focusing action to prevent the energy from being spread unduly. Measurements of the degree of dispersion of the whistlers have been interpreted to yield information about the density of electrons in the atmosphere at very great heights. The density required seems considerably larger than could reasonably have been expected. If the free electrons are produced by ionization of the terrestrial atmosphere its temperature in these regions must be at least 7200 degrees K. The results might alternatively be explained on the assumption that the electrons are falling in from outside, and if this were so it might account for the relationship between the occurrence of whistlers and magnetic activity.

Potential waves for relativistic electron scattering and stochastic acceleration during magnetic storms

Abstract: The possibility of electron stochastic energization to relativisitic energies (≥ 1 MeV) via resonant wave-particle interactions during a magnetic storm is explored. The minimum electron energy Emin for cyclotron resonant interaction with various electromagnetic waves is calculated for conditions representative of storm-times. Since Emin > 1 MeV for resonance with L-mode ion cyclotron waves, intense stormtime EMIC waves could contribute to relativistic electron loss, but not acceleration. Inside the plasmapause whistler mode waves, and highly oblique magnetosonic waves near the lower hybrid frequency, can resonate with electrons over the important energy range from ∼ 100 keV to ∼ 1 MeV. In low density regions outside the plasmapause, the whistler, RX, LO and Z modes can resonate with electrons over a similar energy range. These waves have the potential to contribute to the stochastic acceleration of electrons up to relativistic energies during magnetic storms.