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  • Other Sources  (18)
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  • 1
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    Pc1 pulsations observed by AMPTE/CCE in the earth's outer magnetosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Electromagnetic ion-cyclotron waves in the Pc1-2 frequency range (0.1-5 Hz) have been observed in earth's equatorial magnetosphere over the range L = 3 to 9 by the AMPTE/CCE magnetic-field experiment. Detailed analysis of data from two orbits together with preliminary occurrence statistics from 31 days are reported. One example occurred during disturbed geomagnetic conditions (maximum AE greater than 1000 nT) and exhibited intense Pc1 from L = 5 to the magnetopause (L = about 7.5). The second example occurred during moderate to quiet conditions (average AE = about 300 nT) and displayed Pc1 in two distinct L ranges: low (L = about 4) and high (L greater than 7.5). Statistical results show that Pc1 are about 4 times more common for L greater than 7 than for L less than 6 and occur primarily in the afternoon. The discovery of a statistically dominant outer-magnetospheric source region implies that ring-current interaction with the plasmasphere is not the primary source of Pc1 excitation, but suggests that plasma sheet ions may be a significant energy source for Pc1. This result is consistent with the strong dependence of the linear convective growth rate on magnetic-field strength.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 1853-185
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  • 2
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    First Viking results - Magnetic field measurements (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The magnetic field experiment on the Swedish Viking satellite consists of a triaxial fluxgate magnetometer system with the sensors mounted on a 2-m boom. Transverse magnetic field perturbations are readily observed which identify the large-scale auroral and cusp-region Birkeland current (BC) systems. A sharp gradient was observed in the dayside region near apogee and 08:40 MLT during a pass on March 25, 1986 which has been interpreted as an earthward-flowing BC of 8 micro-A/sq m. When projected to ionospheric altitudes it is estimated that the current density is 200 micro-A/sq m.
    Keywords: GEOPHYSICS
    Type: Physica Scripta (ISSN 0031-8949); 37; 3, Ma; 479-481
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  • 3
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    Resonant geomagnetic field oscillations and Birkeland currents in the morning sector (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The relationship between large-scale Birkeland currents and resonant oscillations of the geomagnetic field is investigated on the basis of Viking magnetic-field, electric-field, and particle measurements and AMPTE-CEE and IMP-8 magnetic-field measurements obtained during April 23-25, 1986. The data are presented in extensive graphs and characterized in detail. The 3-16-mHz 5-60-nT magnetic-field oscillations detected by Viking are also seen by AMPTE-CEE below L = 8.8 and extend from the lower L shells to the boundary between regions 1 and 2 of the Birkeland-current system, and this boundary is shown to be closely related to the interface between the low-latitude boundary layer and the central plasma sheet. It is suggested that the magnetospheric oscillations may be driven by several different solar-wind features, possibly depending on the direction of the IMF.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 2661-267
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  • 4
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    Geomagnetic field-line resonant harmonics measured by the Viking and AMPTE/CCE magnetic field experiments (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The first simultaneous observations of multiple harmonic, azimuthally polarized, ULF pulsations at two points along a geomagnetic flux tube in space are reported. In March 1986, the elliptically orbiting equatorial AMPTE/CCE satellite was oriented with the apogee near 0830 h MLT, and the orbital plane of the polar-orbiting Viking satellite was at 1000 MLT. The satellites were situated within approximately the same flux tube but with an effective separation of approximately 10 R(e) near L = 8 on the inbound pass of the AMPTE/CCE orbit. Structured harmonic pulsations were observed by the magnetic field experiments on both spacecraft, and they appeared to turn off and on simultaneously at both locations. Both the observations and the relative amplitudes along the magnetic field lines support recent ideas of multiple field-line resonances of Alfven waves.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 427-430
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  • 5
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    Observations of large-scale Birkeland currents with Viking (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Data from the Viking Magnetic Field Experiment and Hot Plasma Experiment acquired on March 25, 1986 are analyzed. The large-scale region 1 and region 2 Birkeland current systems (with densities of about 0.1 microA/sq m) were readily identified in the morning sector at altitudes of 12,500 to 13,000 km. Embedded in the large-scale region 1 system are small-scale intense currents that are not necessarily aligned in the east-west geomagnetic direction. The major carriers of the large-scale region 1 Birkeland currents appear to be upward-flowing electrons with energies below 10 eV. Embedded within this flux can be spatially limited regions of 'hotter' electron fluxes that carry small-scale currents. The correlation of magnetic and particle observations obtained here supports previous suggestions that the region 1 currents in the morning sector have their source in the boundary layer and that the region 2 currents are associated with the plasma sheet.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 419-422
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  • 6
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    High latitude currents in the 0600 to 0900 MLT sector - Observations from Viking and DMSP-F7 (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-resolution magnetic field and charged-particle data acquired on March 25, 1986 by the Viking and DMSP-F7 satellites, as they traversed the dawn sector auroral zone on nearly antiparallel trajectories within 40 min of each oher, are analyzed. Magnetic field measurements by Viking at 0850 MLT and by DMSP at 0630 MLT indicate the presence of a large-scale earthward-directed region 1 Birkeland current and an upward-flowing region 2 current. Both satellites also observed a third Birkeland current adjacent to and poleward of the region 1 system with opposite flow. This poleward system is about 0.5 deg invariant latitude wide and has a current density comparable to the region 1 and 2 systems. The highest-latitude current is identified as region 0. Its charged-particle signatures were used to infer field line mapping to the equatorial plane.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 14; 423-426
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  • 7
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    Satellite observations of current and waves in space plasmas (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Plasma processes occurring in the magnetosphere are examined in the light of recent observations of currents and waves with satellite-born magnetic experiments. In particular, results from the Viking and AMPTE/CCE satellites indicate that geomagnetic field lines that guide stationary Birkland currents can also support resonant Alfven waves. The relationship of these waves to the current systems and their source in the magnetosphere is still under investigation. It is emphasized that Birkland currents and Alfven waves are fundamental to an understanding of the earth's plasma environment.
    Keywords: GEOPHYSICS
    Type: Laser and Particle Beams (ISSN 0263-0346); 6; 503-511
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  • 8
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    Observations of the plasma environment during an active ionospheric ion beam injection experiment (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Several sounding rocket flights have been used to clarify the electrodynamics of neutral beam releases of Ar ions in the upper ionosphere, by varying the Ar's point of release with respect to the diagnostic payload. A volume of 10-m radius centered on the Ar release payload is measured for broadband wave activity; the superthermal neutralizing beam electrons become magnetized in this volume for across-field plasma releases, and ambient electrons are accelerated to energies of several hundred eV. This is speculated to be due to wave turbulence rather than payload-neutralization.
    Keywords: GEOPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 10; 7, 19
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  • 9
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    Argon ions injected parallel and perpendicular to the magnetic field (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Preliminary results are reported of measurements obtained with the 0-10-kHz electric-field plasma-wave receivers and single-particle ion detectors of the ARCS-3 sounding-rocket payload over the auroral oval on February 10, 1985, after downward/field-parallel or transverse-spiral injection of Ar ions from the accelerator subpayload (separating itself at 2.3 m/s). The data are presented graphically and briefly characterized. The waves induced by the parallel injections are found to be much weaker than those induced by the perpendicular injections. In addition to the expected response to the Ar beam, an ion flux at pitch angle 90 deg was detected during the second parallel injection.
    Keywords: GEOPHYSICS
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  • 10
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    A comparison of plasma waves produced by ion accelerators in the F-region ionosphere (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Ion beams injected into the ionosphere are known to produce waves related to the normal modes of the plasma. The spectra of plasma waves produced during four sounding rocket experiments are examined. The experimental conditions were somewhat different during each experiment. The accelerated ion was either Xe(+) or Ar(+) and the experimental geometry, described by the separation vector between the plasma wave receiver and the ion accelerator, was either parallel or perpendicular to the geomagnetic field.
    Keywords: GEOPHYSICS
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