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  • 1
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    Observations of double layer-like and soliton-like structures in the ionosphere (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two types of large electric field signatures, individual pulses and pulse trains, were observed on a sounding rocket launched into the afternoon auroral zone on January 21, 1982. The typical electric fields in the individual pulses were 50 mV/m or larger, aligned mostly parallel to B, and the corresponding potentials were at leat 100 mV (kT approximately 0.3 eV). A lower limit of 15 km/sec can be set on the velocity of these structures, indicating that they were not ion acoustic double layers. The pulse trains, each consisting of on the order of 100 pulses, were observed in close association with intense plasma frequency waves. This correlation is consistent with the interpretation of these trains as Langmuir solitons. The pulse trains correlate better with the intensity of the field-aligned currents than with the energetic electron flux.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 11; 511-514
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  • 2
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    Wave rectification in plasma sheaths surrounding electric field antennas (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Combined measurements of Langmuir or broadband whistler wave intensity and lower-frequency electric field waveforms, all at 10-microsecond time resolution, were made on several recent sounding rockets in the auroral ionosphere. It is found that Langmuir and whistler waves are partically rectified in the plasma sheaths surrounding the payload and the spheres used as antennas. This sheath rectification occurs whenever the high frequency (HF) potential across the sheath becomes of the same order as the electron temperature or higher, for wave frequencies near or above the ion plasma frequency. This rectification can introduce false low-frequency waves into measurements of electric field spectra when strong high-frequency waves are present. Second harmonic signals are also generated, although at much lower levels. The effect occurs in many different plasma conditions, primarily producing false waves at frequencies that are low enough for the antenna coupling to the plasma to be resistive.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A11; p. 21,361-21,374
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  • 3
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    Langmuir turbulence in the auroral ionosphere 1: Linear theory (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Intense bursts of Langmuir waves with electric fields of 50 to 500 mV / m have been frequently observed at altitudes greater than 500 km in the auroral ionosphere. These bursts are driven by 20 eV to 4 keV field-aligned electrons, which are embedded in an approximately isotropic nonthermal tail of scattered electrons. The Langmuir bursts are often observed at altitudes where the ionosphere is moderately magnetized (OMEGA (sub e) approximately equals omega (sub pe)). Both the moderate magnetization and the scattered electrons have a major influence on the linear dispersion and damping of Langmuir waves. In particular, the linear dispersion is topologically different depending on whether the magnetic field is subcritical (OMEGA (sub e) less than omega (sub pe)) or supercritical (OMEGA (sub e) greater than omega (sub pe)). The correct dispersion and damping can account for the observed polarization of the Langmuir waves, which is very nearly parallel to the geomagnetic field. Inferred properties of the linear instability driven by the field-aligned electrons are discussed. The linear dispersion and damping derived here provide the basis for a nonlinear turbulence study described in a companion paper (Newman et al., this issue).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A4; p. 6367-6376
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  • 4
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    Impulsive ion injections in the morning auroral region (1995)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Low altitude (less than 1000 km) measurements of ions precipitating into the morning auroral region are presented and analyzed. The ion fluxes exhibited time-energy signatures consistent with impulsive injection onto high-altitude field lines, followed by time-of-flight dispersion. The origin of these ions is investigated through the detailed examination of these signatures in conjunction with simultaneous measurements of precipitating electrons and a magnetic field model. A model is developed which indicates that the source for these particles was located in or near the magnetopause boundary layer, with the position deduced to be in the midlatitude flank region about 20-30 R(sub E) tailward of the Earth. The model explains the existence of multiple injections on a given field line as due to a quasi-periodic source, with the periodicity being about 100-200 s at the source. Several mechanisms are examined in an attempt to explain the injections, with a mechanism related to the propagation of waves on the surface of the boundary layer found to be the most plausible. The observations and results are compared to those of similar experiments and some unifying ideas are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A7; p. 12,133-12,149
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  • 5
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    Evidence of a transverse Langmuir modulational instability in a space plasma (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The auroral ionosphere Langmuir-wave electric field amplitude modulation observations presented may be accounted for by a transverse modulational instability that is resonant with lower hybrid of ion Bernstein waves. In independent observations, the modulation frequencies were near the characteristic frequencies of perpendicular modes. These data strongly suggest the need for two- or three-dimensional model descriptions of nonlinear Langmuir wave evolution in the low-beta plasma.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 18; 1177-118
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  • 6
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    Dual sounding rocket observations of low-altitude electrostatic shocks (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Two sounding rockets were used to simultaneously place two payloads on nearly the same magnetic field lines in the late-evening auroral zone. The dc electric field measurements obtained by the payloads imply a parallel potential of several kV below the higher payload, probably occurring between the two payloads. No possible resistive mechanism in observed in the 100 Hz-10 kKz band which could support the parallel field; this implies the existence of resistance-generating turbulence which are either at other frequencies, or of a type not measured by the probes, or localized parallel potentials not coincident with the payload trajectories.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 12173-12
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  • 7
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    High-resolution sounding rocket observations of large-amplitude Alfven waves (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Shear Alfven waves with amplitudes greater than 100 mV/m were observed on two recent sounding rocket flights. The largest waveforms are best described as a series of step functions, rather than as broadband noise or as single frequency waves. Complete two-dimensional E and B measurements at 4-ms time resolution were made, showing a downward propagation direction and implying insignificant reflection from the ionosphere at frequencies greater than 1 Hz. Intense, field-aligned, low-energy electron fluxes accompany the waves. Acceleration of these electrons by the Alfven waves is shown to be feasible. The waves in at least one case have a sufficently large ponderomotive potential to generate the observed density fluctuations of order one.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 12157-12
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  • 8
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    Structure of an energetic narrow discrete arc (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Particle distributions, waves, dc electric fields, and magnetic fields were measured by two sounding rockets at altitudes of 950 and 430 km through an energetic (greater than 5 keV) narrow (about 10 km) stable discrete arc. Although the payloads' magnetic footprints were separated by only 50 km, differences in the arc's structure were observed including the spatial width, peak energy, and characteristic spectra. The energetic electron precipitation included both slowly varying isotropic fluxes that formed an inverted-V energy-time signature and rapidly varying field-aligned fluxes at or below the isotropic spectral peak. The isotropic precipitation had a flux discontinuity inside the arc indicating the arc was present on a boundary between two different magnetospheric plasmas. Dispersive and nondispersive bursts of field-aligned electrons were measured throughout the arc, appearing over broad energy ranges or as monoenergetic beams. Dispersive bursts gave variable source distances less than 8000 km. Plateauing of some of the most intense bursts suggests that waves stabilized these electrons. During the lower altitude arc crossing, the field-aligned component formed a separate inverted-V energy-time signature whose peak energy was half the isotropic peak energy.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 6533-654
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  • 9
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    Large electric fields in the magnetosphere (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The Langmuir solitonlike structures which contain plasma frequency oscillations of 500 mV/m and parallel electric fields of about 100 mV/m, observed in the auroral zone below 1000 km, are studied. The characteristics of electrostatic shocks that contain perpendicular fields of 1000 mV/m and parallel fields of 100 mV/m, and of double layers that have parallel fields of 10 mV/m are described. Observations of the geomagnetic tail reveal the presence of 100 mV/m turbulent electric fields and 5-10 mV/m quasi-static fields in the high latitude boundary of the plasma sheet, and inside the plasma sheet fields of 5-10 mV/m are detected. The large amplitude quasi-static electric field fluctuations of 100 mV/m and the dc fields of approximately 5 mV/m observed in the bow shock are examined.
    Keywords: GEOPHYSICS
    Type: Space Science Reviews (ISSN 0038-6308); 42; 313-335
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  • 10
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    Field-aligned electron precipitation at the edge of an arc (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Measurements of field-aligned electrons at the edge of an arc are presented from a sounding rocket flight through a quiet afternoon auroral arc. High time resolution measurements show the evolution of the electron distribution function over the 2.3-km width of field-aligned precipitation. A nearly constant 1.2-eV perpendicular temperature was found for these field-aligned fluxes over a broad range of parallel energies (100 - 900 eV). The small perpendicular temperature indicates that the acceleration region is located at a low altitude. Two models of cold plasma convection into the edge of a V-shaped potential structure are examined and found to be consistent with both the observed fluxes and spatial width of the edge precipitation. Both models predict an average source plasma density less than 130/cu cm to account for the observed field-aligned fluxes and thus an acceleration region well above 1000 km.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 1723-173
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