arXiv subjects

M. M. Oppenheim

Publications and source records attributed to M. M. Oppenheim.

5 recordsLinked to original sources

arXiv2016

Formation of plasma around a small meteoroid: 2. Implications for radar head echo

This paper calculates the spatial distribution of the plasma responsible for radar head echoes by applying the kinetic theory developed in the companion paper (Dimant and Oppenheim, arXiv:1608.08524). This results in a set of analytic expressions for the plasma density as a function of distance from the meteoroid. It shows that, at distances less than a collisional mean-free-path from the meteoroid surface, the plasma density drops in proportion to $1/R$ where $R$ is the distance from the meteoroid center; and, at distances much longer than the mean-free-path behind the meteoroid, the density diminishes at a rate proportional to $1/R^{2}$. The results of this paper should be used for modeling and analysis of radar head echoes.

physics.plasm-ph↗

arXiv2016

Formation of plasma around a small meteoroid: 1. Kinetic theory

Every second millions of small meteoroids enter the Earth's atmosphere producing dense plasmas. Radars easily detect these plasmas and researchers use this data to characterize both the meteoroids and the atmosphere. This paper develops a first-principle kinetic theory describing the behavior of particles, ablated from a fast-moving meteoroid, that colliside with the atmospheric molecules. This theory produces analytic expressions describing the spatial structure and velocity distributions of ions and neutrals near the ablating meteoroid. This analytical model will serve as a basis for a more accurate quantitative interpretation of radar measurements and should help calculate meteoroid and atmosphere parameters from radar head-echo observations.

physics.plasm-ph↗

arXiv2011

Magnetosphere-Ionosphere Coupling Through E-region Turbulence 1: Energy Budget

During periods of intense geomagnetic activity, strong electric fields and currents penetrate from the magnetosphere into high-latitude ionosphere where they dissipate energy, form electrojets, and excite plasma instabilities in the E-region ionosphere. These instabilities give rise to plasma turbulence which induces non-linear currents and strong anomalous electron heating (AEH) as observed by radars. These two effects can increase the global ionospheric conductances. This paper analyzes the energy budget in the electrojet, while the companion paper applies this analysis to develop a model of anomalous conductivity and frictional heating useful in large-scale simulations and models of the geospace environment. Employing first principles, this paper proves for the general case an earlier conjecture that the source of energy for plasma turbulence and anomalous heating equals the work by external field on the non-linear current. Using a two-fluid model of an arbitrarily magnetized plasma and the quasilinear approximation, this paper describes the energy conversion process, calculates the partial sources of anomalous heating, and reconciles the apparent contradiction between the inherently 2-D non-linear current and the 3-D nature of AEH.

physics.space-ph↗

arXiv2011

Magnetosphere-Ionosphere Coupling Through E-region Turbulence: Anomalous Conductivities and Frictional Heating

Global magnetospheric MHD codes using ionospheric conductances based on laminar models systematically overestimate the cross-polar cap potential during storm time by up to a factor of two. At these times, strong DC electric fields penetrate to the E region and drive plasma instabilities that create turbulence. This plasma density turbulence induces non-linear currents, while associated electrostatic field fluctuations result in strong anomalous electron heating. These two effects will increase the global ionospheric conductance. Based on the theory of non-linear currents developed in the companion paper, this paper derives the correction factors describing turbulent conductivities and calculates turbulent frictional heating rates. Estimates show that during strong geomagnetic storms the inclusion of anomalous conductivity can double the total Pedersen conductance. This may help explain the overestimation of the cross-polar cap potentials by existing MHD codes. The turbulent conductivities and frictional heating presented in this paper should be included in global magnetospheric codes developed for predictive modeling of space weather.

physics.space-ph↗

arXiv2005

Meteor generated plasma columns in E-region ionosphere: fields and diffusion

A meteoroid penetrating the Earth's atmosphere leaves behind a trail of dense plasma in the E-region ionosphere, a region where electrons are strongly magnetized while ions are demagnetized due to their frequent collisions with neutrals. While radar measurements of meteor trail evolution have been collected and used to infer meteor and atmospheric properties since the 1950s, no accurate quantitative model of trail fields and diffusion exists. This paper describes a theory and simulations of trail plasma physics which applies to the majority of small meteors. Unlike earlier papers, our theory assumes a significant angle between the geomagnetic field and the plasma trail and includes the important interaction between the trail and the background ionospheric plasma. This study provides quantitative knowledge of the spatial distribution and dynamics of the plasma density and electric field. This should enable meteor and atmospheric researchers to more accurately interpret radar observations of specular and non-specular meteor echoes.

physics.plasm-ph↗