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  • 1
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    Physics of magnetospheric boundary layers (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.
    Keywords: GEOPHYSICS
    Type: NASA-CR-197920 , NAS 1.26:197920
    Format: application/pdf
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  • 2
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    Towards an MHD theory for the standoff distance of Earth's bow shock (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: An MHD theory is developed for the stand-off distance a(sub s) of the bow shock and the thickness delta(sub ms) of the magnetosheath, using the empirical Spreiter et al. relation delta(sub ms) = kX and the MHD density ratio X across the shock. The theory includes as special cases the well-known gasdynamic theory and associated phenomenological MHD-like models for delta(sub ms) and a(sub s). In general, however, MHD effects produce major differences from previous models, especially at low Alfven (M(sub A)) and sonic (M(sub S)) Mach numbers. The magnetic field orientation, M(sub A), M(sub S) and the ratio of specific heats gamma are all important variables of the theory. Three principal conclusions are reached. First, the gasdynamic and phenomenological models miss important dependances on field orientation and M(sub S) and generally provide poor approximations to the MHD results. Second, changes in field orientation and M(sub S) are predicted to cause factor of approximately 4 changes in delta(sub ms) at low M(sub A). Third, using Spreiter et al.'s value for k in the MHD theory leads to maximum a(sub s) values at low M(sub A) and nominal M(sub S) that are much smaller than observations and MHD simulations require. Resolving this problem requires either the modified Spreiter-like relation and larger k found in recent MHD simulations and/or breakdown in the Spreiter-like relation at very low M(sub A).
    Keywords: GEOPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 21; 25; p. 2781-2784
    Format: text
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  • 3
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    Interference patterns in the Spacelab 2 plasma wave data - Oblique electrostatic waves generated by the electron beam (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: During the Spacelab 2 mission the University of Iowa's Plasma Diagnostics Package (PDP) explored the plasma environment around the shuttle. Wideband spectrograms of plasma waves were obtained from the PDP at frequencies of 0-30 kHz and at distances up to 400 m from the shuttle. Strong low-frequency (below 10 kHz) electric field noise was observed in the wideband data during two periods in which an electron beam was ejected from the shuttle. This noise shows clear evidence of interference patterns caused by the finite (3.89 m) antenna length. The low-frequency noise was the most dominant type of noise produced by the ejected electron beam. Analysis of antenna interference patterns generated by these waves permits a determination of the wavelength, the direction of propagation, and the location of the source region. The observed waves have a linear dispersion relation very similar to that of ion acoustic waves. The waves are believed to be oblique ion acoustic or high-order ion cyclotron waves generated by a current of ambient electrons returning to the shuttle in response to the ejected electron beam.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 97; A11; p. 17,005-17,018.
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  • 4
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    Interference patterns in the Spacelab 2 plasma wave data: Lower hybrid waves driven by pickup ions (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: During the Spacelab 2 mission the University of Iowa's Plasma Diagnostics Package (PDP) was released from the shuttle to explore the plasma environment around the shuttle. Wideband spectrograms were obtained from the PDP at frequencies from 0 to 30 kHz and distances up to 400 m from the shuttle. The wideband data frequently showed antenna interference patterns when the PDP was on the downstream side of the shuttle. Analysis of these interference patterns allows a determination of the wavelength, the plasma rest frame frequency, the direction of propagation, the power spectrum, and in some cases the location of the source. We concentrate our analysis on interference patterns due to lower hybrid waves: waves which have rest frame frequencies near the lower hybrid frequency and propagate perpendicular to the magnetic field. The waves have an almost flat dispersion relation with frequencies just above the lower hybrid frequency and relatively short wavelengths (1 - 4 m). The observed lower hybrid waves depend strongly on the position of the PDP relative to the shuttle and the magnetic field direction. Our results confirm previous suggestions that the lower hybrid waves are generated primarily in the vicinity of the shuttle and that they are driven by a charge exchange interaction between the ambient ionosphere and a H2O cloud around the shuttle.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A12; p. 21,571-21,580
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  • 5
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    Growth of electron plasma waves above and below f(p) in the electron foreshock (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper investigates the conditions required for electron beams to drive wave growth significantly above and below the electron plasma frequency, f(p), by numerically solving the linear dispersion equation. It is shown that kinetic growth well below f(p) may occur over a broad range of frequencies due to the beam instability, when the electron beam is slow, dilute, and relatively cold. Alternatively, a cold or sharp feature at low parallel velocities in the distribution function may drive kinetic growth significantly below f(p). Kinetic broadband growth significantly above f(p) is explained in terms of faster warmer beams. A unified qualitative theory for the narrow-band and broad-band waves is proposed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 7307-731
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  • 6
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    A theory for the Langmuir waves in the electron foreshock (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A comprehensive theory for the Langmuir waves in the earth's foreshock involving saturation of the kinetic version of the beam instability by quasi-linear relaxation is proposed in this paper. Reactive and kinetic beam instabilities are shown to be the two limiting versions of a single instability whose analytically and numerically derived descriptions are shown to form a consistent picture. It is pointed out that the reactive instability gives rise only to narrow-band growth while the kinetic instability gives rise to wide-band growth. Arguments for describing the Langmuir wave growth in terms of the kinetic instability are given, and four suppression mechanisms for the kinetic instability are discussed. It is suggested that quasi-linear relaxation limits the Langmuir growth and gives rise to distributions qualitatively similar to the observed distribution functions, and arguments in favor of this hypothesis are presented.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 2329-234
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  • 7
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    A semiquantitative theory for the 2f(p) radiation observed upstream from the earth's bow shock (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: In this paper, Cairns and Melrose's (1985) theory for the second harmonic of the plasma frequency f(p), i,e, 2f(p) radiation, is extended into a detailed semiquantitative theory for the 2f(p) radiation observed upstream from the earth's bow shock. It is shown that the 2f(p) radiation grows by the process L + L going to T + S (where L, S, and T denote Langmuir, ion acoustic, and transverse electromagnetic waves, respectively), proceeding in two 3-wave steps in the two wings of the foreshock. The theory developed here is consistent with all the available wave data.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 3958-396
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  • 8
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    A theory for the radiation at the third to fifth harmonics of the plasma frequency upstream from the earth's bow shock (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A theory involving the process L + T' - T is proposed for the observed third to fifth harmonics of the plasma frequency observed upstream from the earth's bow shock. The conditions for which the theory may explain the observed radiation are determined, and the viability of the theory is discussed. The theory is found to require L waves with temperature between about 10 to the 21st and 10 to the 22nd K in the source regions to account for the levels and number of harmonics of the observed radiation. Such L wave temperatures are theoretically possible in the foreshock, but are not consistent with the most intense observed L waves.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 858-866
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  • 9
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    The electron distribution function upstream from the earth's bow shock (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A general analytic theory for the distribution function of particles backstreaming from an arbitrary shock in a magnetized plasma is presented. Particle motions are shown to be restricted to two-dimensional planes. A general form for the source term describing upstreaming particles accelerated at the shock is presented along with explicit source terms for planar and parabolic shocks. The origin and form of the escape velocity cutoff for a shock in a magnetized plasma are discussed. The distribution function upstream of a finite planar shock and a parabolic shock in two dimensions is calculated, and an analytic approximation of the cutoff velocity at points in the upstream region is derived. The theory is then applied to the earth's bow shock, calculating distribution functions and the nature and spatial variation of the cutoff velocity. The theory for the particle distribution upstream of the bow shock is compared with the model of Filbert and Kellogg (1979).
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 2315-232
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