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Results for “MAGNETOSPHERIC ELECTRON DENSITY”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

A parametric study of electron multiharmonic instabilities in the magnetosphere

This paper presents numerical calculations of spatial growth rates of multiharmonic electron-cyclotron instabilities driven by a loss-cone energetic distribution, in the presence of colder electrons. When the cold electron density is comparable to the hot, nonconvective instability is possible in harmonic bands below or including the cold upper-hybrid frequency. When the cold electron density is larger than the hot, nonconvective instability is possible only in that band containing the cold upper-hybrid frequency. Increasing the cold electron temperature in relation to the hot eventually removes all nonconvective behavior. Convective instability is still possible above the cold upper-hybrid frequency.

Ashour-Abdalla, M.↗
NASA NTRS1972

Modulational instability of whistlers in cold plasmas

The paper obtains the modulational stability spectrum of whistlers in cold plasmas taking into consideration both ion motion and relativistic effects. The unstable band is contiguous to Omega sub e/4 and, depending on the plasma density, lies above or below that frequency Omega sub e is the electron cyclotron frequency of the static magnetic field. The relevance of the instability to whistlers in the magnetosphere is discussed.

Brinca, A. L.↗
NASA NTRS1976

Evidence that pitch angle scattering is an important loss mechanism for energetic electrons in the inner radiation belt of Jupiter

Analysis of data from the Pioneer 10 flyby discloses that pitch angle scattering plays an important part in determining the distribution of energetic electrons in the inner magnetosphere of Jupiter. Angular distributions measured by a Cerenkov detector reveal that redistribution takes place in pitch angle. Additionally, the radial profile of phase space density along the equator demands simultaneous particle losses. The loss rates are too high to be accounted for by synchrotron radiation loss, but are reasonably attributed to pitch angle scattering into the planetary loss cone.

Fillius, W.↗
NASA NTRS1982

Thermal fluctuations and the diffuse electrostatic emissions

The suggestion that the weak-banded electrostatic emissions observed in the magnetosphere at frequencies between the electron gyrofrequency and upper hybrid frequency are thermal fluctuations is quantitatively explored, by means of a hot-cold model for dayside electron distributions with density and temperature ratios much greater than unity. It is determined that, for typical dayside conditions, the observed waves are weakly damper Bernstein-Harris modes whose spectral density and polarization, perpendicular to the ambient magnetic field, can be accounted for by the theory. It is suggested that the formalism developed may be applicable to weak electron cyclotron emissions at Jupiter and Saturn, and can be extended to lower-frequency ion cyclotron fluctuations by modifying the theory to include ion contributions.

Sentman, D. D.↗
NASA NTRS1998

Magnetospheric Constellation and Tomography Mission Concept

We describe the basic principles, instrumentation, and feasibility of a multi-satellite mission that combines in situ observations of plasma and electromagnetic fields with radio tomography imaging. We show that a 16-satellite radio tomography experiment can produce two-dimensional images of plasma density in the earth's magnetosphere at sufficient spatial (1/2 R(sub E)) and temporal (approximately 10s) resolution to address key problems of magnetospheric physics. The same mission can incorporate electron and ion analyzers, magnetometers, and electric field instruments on the same spacecraft. We suggest that the large-scale images are more valuable when combined with in situ observations, supporting an unambiguous interpretation of the in situ data and an investigation of the interdependence of small- and large-scale plasma processes.

Ergun, R. E.↗
NASA NTRS2021

Particle Acceleration by Dense Impulsive Structures Moving in Ambient Magnetospheric Plasma. 3-D Hybrid Kinetic Modeling and MMS Observations

High resolution observations of dense plasma impulsive structures moving through an ambient background magnetospheric flows were captured by the Magnetospheric Multiscale mission. The observations show particle heating and acceleration, shock-like wave formation, and whistler wave excitation inside the interface between the dense impulsive plasma structures and the ambient plasma. A multiscale hybrid kinetic simulation provides an explanation of the observed wave-particle interactions with the assumption that the dense plasma structures may be represented by plasma clouds which are formed at the magnetopause layer due to reconnection processes. Plain Language Summary: Dense, impulsive plasma structures moving through a background plasma were captured by the NASA Magnetospheric Multiscale mission. The observations show that the dense structures can generate strong perturbations in the electromagnetic field and shock-like waves. Interactions between these electromagnetic waves and the particles results in particle acceleration. 3-D hybrid kinetic modeling (particle description for ions and fluid description for electrons) was used to investigate the plasma physics of the observed structures. It was assumed that the plasma clouds were formed by magnetic field reconnection inside the magnetopause, which is the interface between the solar wind particles and the cold low-density magnetospheric plasma. The work helps us understand the plasma environment at the interface between the Earth and solar wind, near planetary moons, within astrophysical explosions, and possibly at the interface between the solar wind and local interstellar medium.

A. S. Lipatov↗
NASA NTRS2016

Electron Flux Models for Different Energies at Geostationary Orbit

Forecast models were derived for energetic electrons at all energy ranges sampled by the third-generation Geostationary Operational Environmental Satellites (GOES). These models were based on Multi-Input Single-Output Nonlinear Autoregressive Moving Average with Exogenous inputs methodologies. The model inputs include the solar wind velocity, density and pressure, the fraction of time that the interplanetary magnetic field (IMF) was southward, the IMF contribution of a solar wind-magnetosphere coupling function proposed by Boynton et al. (2011b), and the Dst index. As such, this study has deduced five new 1 h resolution models for the low-energy electrons measured by GOES (30-50 keV, 50-100 keV, 100-200 keV, 200-350 keV, and 350-600 keV) and extended the existing >800 keV and >2 MeV Geostationary Earth Orbit electron fluxes models to forecast at a 1 h resolution. All of these models were shown to provide accurate forecasts, with prediction efficiencies ranging between 66.9% and 82.3%.

Boynton, R. J.↗
NASA NTRS1972

Universal instability associated with the plasmapause and its role in geomagnetic micropulsations.

The observed close correlation between the plasmapause and micropulsations is explained on the basis of a universal instability model. Both theoretical and experimental studies of a nonhomogeneous magnetoplasma indicate that a steep plasma density gradient at the plasmapause is likely the origin of the universal instability in the magnetosphere. Drift waves excited at the plasmapause may be unstable in the direction of the electron drift and propagate eastward nearly perpendicularly to the magnetic field. The drift waves, however, tend to convert very quickly to ion sound or Alfven waves with a much larger phase velocity parallel to the magnetic field. This may be a possible source mechanism for rather regular geomagnetic micropulsations, and specific mechanisms are identified for the long- and short-period cases.

Kikuchi, H.↗
NASA NTRS1974

Initial observations of plasma electrons from the Pioneer 10 flyby of Jupiter

Initial results are presented from the electron measurements made by the Ames Research Center Plasma Analyzer during the inbound passage of Pioneer 10 in the vicinity of Jupiter. The observations indicate that as in the case of the earth's magnetosheath, there is an increase in electron temperature across the Jovian bow shock. During the second extended magnetosheath traversal (approximately 54 to 46.5 Jupiter radii) the electron temperatures were generally higher than those observed during the first magnetosheath traversal (109 to 96 Jupiter radii). These higher electron temperatures are in agreement with the measured higher magnitude of the magnetic field and ion density during this traversal. These observations are consistent with the contraction of the Jovian magnetosphere due to an increase in the solar wind dynamic pressure.

Intriligator, D. S.↗
NASA NTRS1979

Plasma injection and diamagnetism

A detailed study of the diamagnetic properties of magnetospheric plasma injected at synchronous altitudes is presented. Defining the magnetic induction field B = H + 4piM, the magnetization M is computed from the plasma distribution functions and it is shown that the diamagnetic contribution of the particles having energies of 100 eV to 81 eV can completely account for observed changes in the magnetic induction energy density. Computation of the resulting magnetic field H indicates that the current system in the magnetosphere is complex. Significant changes in H have been observed in a few minutes time scale. Studies of the particle density at various magnetic moments show that both protons and electrons together or individually act to cause the diamagnetic variations in B.

Gurgiolo, C.↗
NASA NTRS1991

The plasma environment of Uranus

An overview of the observational results on the plasma environment at Uranus is given, and the implications of these observations for magnetospheric physics at Uranus are discussed. During the Voyager 2 encounter with Uranus, an extended magnetosphere filled with a tenuous plasma was detected. This low-energy plasma was found to consist of protons and electrons, with no significant heavy ion contribution, and with a density in the regions sampled by the spacecraft of at most three electrons per cubic centimeter. The plasma electrons and ions exhibit both a thermal component (with temperatures of tens of eV) and a hot component (with temperatures of a few keV). The thermal ion component is observed both inside and outside an L-shell value near 5, whereas the hot ion and electron component is excluded from the region inside of that L-shell. The source of the thermal component of the plasma is either the planetary ionosphere or the neutral hydrogen corona surrounding Uranus, whereas the hot component is convected in from the magnetotail, with probably an ionospheric source.

Belcher, J. W.↗
NASA NTRS2015

Relativistic Electron Response to the Combined Magnetospheric Impact of a Coronal Mass Ejection Overlapping with a High-Speed Stream: Van Allen Probes Observations

During early November 2013, the magnetosphere experienced concurrent driving by a coronal mass ejection (CME) during an ongoing high-speed stream (HSS) event. The relativistic electron response to these two kinds of drivers, i.e., HSS and CME, is typically different, with the former often leading to a slower buildup of electrons at larger radial distances, while the latter energizing electrons rapidly with flux enhancements occurring closer to the Earth. We present a detailed analysis of the relativistic electron response including radial profiles of phase space density as observed by both Magnetic Electron and Ion Sensor (MagEIS) and Relativistic Electron Proton Telescope instruments on the Van Allen Probes mission. Data from the MagEIS instrument establish the behavior of lower energy (<1 MeV) electrons which span both intermediary and seed populations during electron energization. Measurements characterizing the plasma waves and magnetospheric electric and magnetic fields during this period are obtained by the Electric and Magnetic Field Instrument Suite and Integrated Science instrument on board Van Allen Probes, Search Coil Magnetometer and Flux Gate Magnetometer instruments on board Time History of Events and Macroscale Interactions during Substorms, and the low-altitude Polar-orbiting Operational Environmental Satellites. These observations suggest that during this time period, both radial transport and local in situ processes are involved in the energization of electrons. The energization attributable to radial diffusion is most clearly evident for the lower energy (<1 MeV) electrons, while the effects of in situ energization by interaction of chorus waves are prominent in the higher-energy electrons.

Magnetosphere↗
NASA NTRS1974

The origin and propagation of chorus in the outer magnetosphere

Wave normals of chorus in the outer magnetosphere have been determined for the first time from data obtained with the Ogo 5 search coil magnetometer. These measurements combined with simultaneous information concerning geomagnetic field, plasma density, and the electron energy and pitch angle distributions provide a consistent picture of the generation, propagation, and subsequent damping of chorus in agreement with theory. Specifically, the data are consistent with chorus generation within 25 deg of the equatorial plane on the dayside and within 2 deg on the nightside. Chorus is generated by a Doppler-shifted cyclotron resonance with electrons between 5 and 150 keV but only when the pitch angle distribution is peaked at 90 deg to the local magnetic field and the anisotropy exceeds a critical value.

Burton, R. K.↗
NASA NTRS1977

Incoherent scatter radar observations during August 4-7, 1972

E- and lower F-region data obtained by the incoherent scatter radar of Chatanika, Alaska were used to analyze the height-integrated Hall and Pedersen conductivities, electric fields, ionospheric currents, electron densities, and rate of heating of the neutral atmosphere by particle precipitation and by electric current dissipation during the period of intense solar flares, August 4-7, 1972. Although the magnetosphere was unusually disturbed magnetically, the radar data were in general not particularly larger than those seen during more quiet periods. Chatanika seemed to be in the auroral oval during nearly the whole of the time period studied, implying a greatly expanded size of the oval.

Weddle, T.↗
NASA NTRS1977

Injun 5 observations of vehicle potential fluctuations at 2500 km

The AFGL spherical electrostatic analyzers aboard the polar orbiting Injun 5 satellite were designed to measure the temperature and density of the plasma as well as the vehicle potential. Significant vehicle potential fluctuations were observed at altitudes near 2500 km in the nighttime, topside ionosphere. At auroral latitudes, precipitating magnetospheric electrons frequently drove the satellite to such strongly negative potentials that the ambient electrons were shielded from instruments. In such cases, simultaneous measurements can be used to calculate the vehicle potential. Potentials of up to -40 volts were observed during impulsive precipitation events. Within the plasma trough, vehicle potentials varied between -1.5 and -4 volts, as compared with the -0.5 to -1 volt observed in the polar cap. The source of this vehicle potential enhancement was ascribed to fluxes of photoelectrons that have escaped from the sunlit conjugate ionosphere.

Sagalyn, R. C.↗
NASA NTRS1980

The structure of the Jovian magnetotail from plasma wave observations

Plasma wave measurements from the outbound passes of Voyager 1 and 2 are used to study the plasma density and structure of the Jovian magnetotail. Two principal types of plasma waves are observed in the magnetotail, continuum radiation and narrowband emissions near the electron gyrofrequency. The low frequency cutoff of the continuum radiation can be used to determine the local electron density. Profiles of the electron density from the outbound passes of Voyager 1 and 2 provide evidence of a broad region of nearly uniform plasma density between the magnetopause and the inner corotating portion of the magnetosphere. We refer to this region as the boundary layer. Comparisons are made with other experimental and theoretical evidence for the existence of such a boundary layer inside the Jovian magnetosphere.

Gurnett, D. A.↗
NASA NTRS1983

Synchrotron radiation as a probe of the inner magnetosphere of Jupiter

A short review is given on the characteristics of Jupiter's inner magnetosphere derived from radio observations in the decimetric wavelength range. A comparison of the data with sophisticated model calculations yields information on the magnetic field configuration and the electron distribution, its density, energy spectrum, and pitch angle dependence as a function of spatial coordinates. The latter information can be used to derive, e.g., the radial diffusion parameters plus the effects of the satellites, Jupiter's ring, and wave-particle interactions upon the electron distribution.

De Pater, I.↗
NASA NTRS2018

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies.

Magnetospheric Multiscale↗