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  • 1
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    High-frequency electrostatic waves near earth's bow shock (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Electrostatic wave measurements from the Active Magnetospheric Particle Tracer Explorer Ion Release Module have been used to investigate the wave modes and their possible generation mechanisms in the earth's bow shock and magnetosheath. It is demonstrated that electrostatic waves are present in the bow shock and magnetosheath with frequencies above the maximum frequency for Doppler-shifted ion acoustic waves, yet below the plasma frequency. Waves in this frequency range are tentatively identified as electron beam mode waves. Data from 45 bow shock crossings are then used to investigate possible correlations between the electrostatic wave properties and the near-shock plasma parameters. The most significant relationships found are anticorrelations with Alfven Mach number and electron beta. Mechanisms which might produce electron beams in the shock and magnetosheath are discussed in terms of the correlation study results. These mechanisms include acceleration by the cross-shock electric field and by lower hybrid frequency waves. A magnetosheath 'time of flight' mechanism, in analogy to the electron foreshock region, is introduced as another possible beam generation mechanism.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 13397-13
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  • 2
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    Analysis and interpretation of the shocklike electrostatic noise observed during the AMPTE solar wind lithium releases (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: During the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind lithium release on September 11, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP-6 and ISEE-1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the Earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam-plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the Earth's bow shock suggest that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud.
    Keywords: GEOPHYSICS
    Type: AD-A168021 , Journal of Geophysical Research (ISSN 0148-0227); 91; 1301-131
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  • 3
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    Plasma waves associated with the AMPTE artificial comet (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Numerous plasma wave effects were detected by the AMPTE/IRM spacecraft during the artificial comet experiment on December 27, 1984. As the barium ion cloud produced by the explosion expanded over the spacecraft, emissions at the electron plasma frequency and ion plasma frequency provided a determination of the local electron density. The electron density in the diamagnetic cavity produced by the ion cloud reached a peak of more than 5 x 10 to the 5th per cu cm, then decayed smoothly as the cloud expanded, varying approximately as t exp-2. As the cloud began to move due to interactions with the solar wind, a region of compressed plasma was encountered on the upstream side of the diamagnetic cavity. The peak electron density in the compression region was about 1.5 x 10 to the 4th per cu cm. Later, a very intense (140 mVolt/m) broadband burst of electrostatic noise was encountered on the sunward side of the compression region. This noise has characteristics very similar to noise observed in the earth's bow shock, and is believed to be a shocklike interaction produced by an ion beam-plasma instability between the nearly stationary barium ions and the streaming solar wind protons.
    Keywords: GEOPHYSICS
    Type: AD-A163458 , Geophysical Research Letters (ISSN 0094-8276); 12; 851-854
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  • 4
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    Electron cyclotron harmonic waves observed by the AMPTE-IRM plasma wave experiment following a lithium release in the solar wind (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: An unexpected occurrence following the second lithium release by the AMPTE-IRM spacecraft in the solar wind on September 20, 1984, was the appearance of electron cyclotron harmonic emissions. These emissions began about 50 s after the release and continued for several minutes. Narrow-band emissions polarized perpendicular to the magnetic field with amplitudes of approximately 0.00001 V/m were observed in each of the first five harmonic bands. The diffuse emissions extended from below the lowest measured frequency channel to above the highest narrow-band emission with a maximum below the electron cyclotron frequency. It will be shown that these observations are inconsistent with their generation by several ion beam instabilities.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 5768-577
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  • 5
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    Electron plasma waves in the solar wind - AMPTE/IRM and UKS observations (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Selected events of plasma wave and electromagnetic emissions in the earth's electron fore-shock region have been studied. Strong emissions are observed in the plasma-wave band when the site of the satellite is magnetically connected to the bow shock. These emissions are generally highly fluctuating. Under certain conditions one observes electromagnetic radiation at the second harmonic produced locally. Electromagnetic emission generated at a position far away from the site of the spacecraft is occasionally detected giving rise to remote sensing of the bow shock. These emissions are related to energetic electron fluxes.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 1 19; 93-96
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  • 6
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    Observation of nonlinear wave decay processes in the solar wind by the AMPTE IRM plasma wave experiment (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Nonlinear wave decay processes have been detected in the solar wind by the plasma wave experiment aboard the Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM spacecraft. The main process is the generation of ultralow-frequency ion acoustic waves from the decay of Langmuir waves near the electron plasma frequency. Frequently, this is accompanied by an enhancement of emissions near twice the plasma frequency. This enhancement is most likely due to the generation of electromagnetic waves from the coalescence of two Langmuir waves. These processes occur within the electron foreshock in front of the earth's bow shock.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 5865-587
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  • 7
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    AMPTE IRM observations of waves associated with flux transfer events in the magnetosphere (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The AMPTE IRM wave instrument has been applied to the study of flux transfer events (FTE's). This initial investigation concentrates on FTE's observed in the magnetosphere during the fall of 1984. The wave morphology consists of four significant features: at frequencies below the ion gyrofrequency, magnetic fluctuations occur with amplitudes of the order of 1 nT; at frequencies from a few hertz to a few hundred hertz, electric field fluctuations are observed which have a broadband amplitude of a few millivolts per meter, which are perpendicularly polarized at the lowest frequencies, and which are partly electrostatic and partly electromagnetic; in the frequency range from 100 Hz to 10 kHz, broadband spikelike waves occur with a time-averaged amplitude of about 0.1 mV/m; and near the electron plasma frequency, bursts of waves occur at the boundaries of FTE's. In none of the 25 events surveyed does the total broadband amplitude of all the waves exceed a few millivolts per meter, an amplitude far too small to provide the dissipation required by 'traditional' reconnection models in which the dissipation region has a thickness the order of an ion gyroradius. Thus, either all of the FTE's are observed at some distance from the diffusion region, or the observable waves play no significant role in the diffusion process, or 'traditional' reconnection models do not apply to reconnection in FTE's.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 5827-584
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  • 8
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    Observations of the artificially injected Porcupine xenon ion beam in the ionosphere (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Results are given of ion beam injection experiments performed in the auroral ionosphere in connection with the German Sounding Rocket Project Porcupine. A heavy (xenon) ion beam was injected into the collisionless ionospheric plasma approximately perpendicular to the ambient magnetic field at altitudes from 190 km to about 450 km. The beam propagates nearly undistorted across the plasma because it is essentially depolarized; at the same time the beam is not current neutralized. This unexpected behavior poses the interconnected problems of how the beam manages to become charge neutralized, how current closure is maintained, and what is the mechanism of depolarization.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 287-303
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