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  • GEOPHYSICS  (28)
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  • 1
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    Wave-particle interactions on the FAST satellite (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: NASA's Fast Auroral Snapshot, or 'FAST' satellite, scheduled for launch in 1993, will investigate the plasma physics of the low altitude auroral zone from a 3500-km apogee polar orbit. FAST will give attention to wave, double-layer, and soliton production processes due to electrons and ions, as well as to wave-wave interactions, and the acceleration of electrons and ions by waves and electric fields. FAST will employ an intelligent data-handling system capacle of data acquisition at rates of up to 1 Mb/sec, in addition to a 1-Gbit solid-state memory. The data need be gathered for only a few minutes during passes through the auroral zone, since the most interesting auroral phenomena occur in such narrow regions as auroral arcs, electrostatic shocks, and superthermal electron bursts.
    Keywords: GEOPHYSICS
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  • 2
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    Magnetic field-aligned particle precipitation (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Magnetic field-aligned particle fluxes are a common auroral phenomenon. Precipitating field-aligned electrons are seen in the vicinity of auroral arcs as suprathermal bursts, as well as superimposed on the more isotropic inverted V electron precipitation. Electron distribution functions reveal two distinct source populations for the inverted V and field-aligned electron components, and also suggest possible acceleration mechanisms. The inverted V electrons are a hot, boundary plasma sheet population that gains the full parallel acceleration. The field-aligned component appears to originate from cold ionospheric electrons that may be distributed throughout the acceleration region. A turbulent parallel field might explain the apparent lifetime of cold electrons in the acceleration region.
    Keywords: GEOPHYSICS
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  • 3
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    The effect of microscopic turbulence on magnetosphere-ionosphere coupling (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The effect of turbulence on the coupling of the magnetosphere and ionosphere has been investigated by including an effective collision frequency in the electron equation of motion. When this term is combined with the continuity equation, the ion equation of motion and Maxwell's equations, a dispersion relation for the kinetic Alfven wave including effective collisions is found. The wave-particle interaction leads to a strong damping of the wave. Inclusion of the effects of plasma sheet kinetics yields a scale size transverse to the magnetic field which corresponds to the size of visual auroral arcs.
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters; 8; Mar. 198
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  • 4
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    Solar wind ion injections in the morning auroral oval (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Energy versus time dispersion of precipitating ion bursts was observed during two rocket flights in the morning auroral oval. Individual bursts lasted about 20 seconds and repeated on a time scale of 100 seconds. The dispersion is interpreted as energy-dependent time-of-flight delay which provides identification of ion charge-to-mass ratio as well as injection source distance. The data are consistent with injections of magnetosheath ions with injection distances ranging from 7 to 19 earth radii. Individual events extended over a regin of at least several degrees of magnetic longitude and 0.3 degrees of invariant latitude. It is suggested that these events are associated with turbulent plasma entry into the magnetospheric entry layer.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; June 1
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  • 5
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    Evidence for parallel electric field particle acceleration in the dayside auroral oval (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Electron and ion energy spectra and electron pitch angle distributions are presented for two sounding rocket flights in the dayside auroral zone. At times, effects of dc electric fields parallel to the magnetic field are evident in that: (1) within precipitation features, protons are decelerated by an amount of energy consistent with that which electrons gain and (2) electrons are sometimes aligned to within 3 deg (full width at half maximum) of the magnetic field. A maximum altitude for the accelerating region of several thousand kilometers is deduced from the narrow width of the pitch angle distribution and also from time-of-flight delays between the observation of accelerated electrons and decelerated protons.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 85; June 1
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  • 6
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    On the origin and spatial extent of high-latitude F region irregularities (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Evidence for the direct production of macroscale irregularities by structured, soft electron fluxes is employed to form the basis for a model for the transport and decay of such structures and the role of plasma instabilities in the production of smaller irregularities. Large scale structures were defined with wavelengths of at least 10 km, intermediate between 0.0-10 km, and short less than 10 m. Data were gathered by means of a rocket flight into the auroral oval and radar scans of 10-350 km altitudes for electron density contours. The radar data indicated that the large-scale structure in the F region plasma was in the main due to electron precipitation. The instability of the structures caused the emergence of smaller scale irregularities in a dynamic balance of instability growth and damping. Additional productive sources which allow the greater than 100 km structures to pass over the North Pole intact are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research; 87; June 1
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  • 7
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    Observations of double layer-like and soliton-like structures in the ionosphere (1984)
    In:  Other Sources
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    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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  • 8
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    Simulations of beam excited minor species gyroharmonics in the Porcupine experiment (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An active experiment for the study of wave particle interaction in the presence of a perpendicular beam type distribution is considered. The experiment involves the injection of a beam perpendicular to the magnetic field. Beam parameters can then be varied while local plasma parameters and associated wave phenomena are measured. Such an experiment was conducted as part of the Porcupine project. The present investigation has the objective to explain theoretically and by means of plasma particle simulations, some of the wave observations obtained. In the experiment, a main rocket payload and four subpayloads were employed. The subpayloads were ejected radially in different directions at an altitude of 240 km. One of the spinning subpayloads contained a plasma gun which emitted a beam of 200 eV xenon ions toward the main payload. The data recorded on the main payload revealed the existence of electrostatic waves with peaks at hydrogen gyroharmonics. A series of computer simulations approximating the xenon experiment was performed. The interpretation of the data is discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; Oct. 1
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  • 9
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    Variable frequency VLF signals in the magnetosphere Associated phenomena and plasma diagnostics (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Coherent variable-frequency signals (ramps) extending from 1 to 8 kHz, injected into the magnetosphere from Siple Station, Antarctica (L=4.3), exhibit upper and lower cutoffs when received at the conjugate station, Roberval, Quebec. Ramp group delay measurements and ionospheric sounding data are used to determine the cold plasma density and L shell of the propagation path. Relationships among f, df/dt, and the 'phase equator' for gyroresonance are calculated using second-order resonance equations generalized to relativistic electrons. The concept thereby introduced is used to develop a diagnostic technique which, for an assumed g(alpha)(v exp -n) electron distribution, provides an estimate of the energy dependence n. Additional aspects of the magnetospheric response to ramp injection, such as emission triggering, curvature due to dispersion, and amplitude saturation, are discussed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 1507-152
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  • 10
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    On the anticorrelation of the electric field and peak electron energy within an auroral arc (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present investigation is concerned with an example of a strongly anticorrelated electric field and particle precipitation, taking into account an application of an extended version of the model of Evans et al. (1977) to the data. A striking feature of the data reported is the high degree of anticorrelation between electric field strength and peak precipitating electron energy. A simple model consisting of a constant current traversing a region in which the conductivities increase in proportion to ionospheric energy deposition provides a qualitative explanation of the observations. However, when the effects of neutral winds, ionization transport, Hall currents, and arc motion, and the nonlinearity of the relationship between peak precipitating electron energy and equilibrium are considered, the conclusions become less clear.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 399-408
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