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  • 1
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    A simulation of the IPS variations from a magnetohydrodynamical simulation (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Calculations of the variations of interplanetary scintillation (IPS) from a disturbance simulated by a 3-D magnetohydrodynamical (MHD) model of the solar wind are presented. The simulated maps are compared with observations and it is found that the MHD model reproduces the qualitative features of observed disturbances. The disturbance produced by the MHD simulation is found to correspond in strength with the weakest disturbance which can be reliably detected by existing single station IPS observations.
    Keywords: PLASMA PHYSICS
    Type: Alabama Univ., Huntsville. STIP Symposium on Physical Interpretation of Solar(Interplanetary and Cometary Intervals; p 54
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  • 2
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    An adaptive grid, unsteady model for two-dimensional magnetohydrodynamic (MHD) flow (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An adaptive grid finite difference method for solving multi-dimensional, time-dependent, magnetohydrodynamic (MHD) equations is developed. The method is capable of solving problems that include high gradients due to geometry, propagation of shock waves and unsteady boundary conditions. The grid generation technique is based on variational principles with direct control over grid concentration, smoothness and skewness. An example for a two-dimensional MHD simulation of the propagation of a solar-flare-generated shock wave in solar wind flow in the heliographic equatorial plane is selected for illustration of this method.
    Keywords: PLASMA PHYSICS
    Type: AIAA PAPER 87-1218
    Format: text
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  • 3
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    Plasma heating at collisionless shocks due to the kinetic cross-field streaming instability (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Heating at collisionless shocks due to the kinetic cross-field streaming instability, which is the finite beta (ratio of plasma to magnetic pressure) extension of the modified two stream instability, is studied. Heating rates are derived from quasi-linear theory and compared with results from particle simulations to show that electron heating relative to ion heating and heating parallel to the magnetic field relative to perpendicular heating for both the electrons and ions increase with beta. The simulations suggest that electron dynamics determine the saturation level of the instability, which is manifested by the formation of a flattop electron distribution parallel to the magnetic field. As a result, both the saturation levels of the fluctuations and the heating rates decrease sharply with beta. Applications of these results to plasma heating in simulations of shocks and the earth's bow shock are described.
    Keywords: PLASMA PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 123-136
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  • 4
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    Induced emission of radiation near 2(omega sub e) by a synchrotron-maser instability (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In the literature, the emission of radiation at 2(omega sub e), where omega sub e denotes the electron plasma frequency, is usually explained as having been produced by the nonlinear interaction of two Langmuir waves via a backscattering process. Since the emission is frequently observed in solar radio bursts, the mechanism has attracted considerable theoretical interest. In the present paper a model is proposed based on a synchrotron-maser instability excited by a hollow beam of moderately relativistic electrons in a plasma, in which the plasma frequency is much higher than the gyrofrequency. An important conclusion is that, as a result of this instability, unpolarized electromagnetic waves with frequencies near 2(omega sub e) may be amplified.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 28; 846-853
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  • 5
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    Electron-cyclotron maser instability caused by hot electrons (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The electron-cyclotron maser instability is studied for energetic electrons with a loss-cone distribution. The instability can occur at all angles of propagation for a wide range of parameters. The growth rate is significantly reduced by the presence of a population of cold electrons, and the instability can be suppressed if the density of the cold electrons is sufficiently large and the temperature of the energetic electrons is not too high.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 28; 2751-275
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  • 6
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    A Three-Dimensional, Time-Dependent Numerical Modeling of Super-Sonic, Super-Alfvenic MHD Flow (1988)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: A three-dimensional, time-dependent, MHD disturbance propagating through a steady inhomogeneous MHD flow is analyzed by a numerical model based on the Lax-Wendroff finite difference method. The initial steady MHD flow is assumed to be supersonic and super-Alfvenic. The background steady MHD flow is obtained by dropping the time-dependent terms in the unsteady MHD equations. A transient MHD disturbance corresponding to a MHD shock is generated at the lower radial boundary surface. The resulting development and propagation of 3-D MHD disturbances interacting with the background steady MHD flow are numerically simulated in this first application to the field of interplanetary physics. Detailed descriptions of the mathematical formulation and numerical methodology are presented. Example computations are performed to demonstrate the validity of the formulation and the capabilities of the model.
    Keywords: PLASMA PHYSICS
    Type: Computers and Fluids (ISSN 0045-7930); 16; 1 19; 81-103
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  • 7
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    Magnetohydrodynamic (MHD) analyses of various forms of activity and their propagation through helio spheric space (1987)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Theoretical and numerical modeling of solar activity and its effects on the solar atmosphere within the context of magnetohydrodynamics were examined. Specifically, the scientific objectives were concerned with the physical mechanisms for the flare energy build-up and subsequent release. In addition, transport of this energy to the corona and solar wind was also investigated. Well-posed, physically self-consistent, numerical simulation models that are based upon magnetohydrodynamics were sought. A systematic investigation of the basic processes that determine the macroscopic dynamic behavior of solar and heliospheric phenomena was conducted. A total of twenty-three articles were accepted and published in major journals. The major achievements are summarized.
    Keywords: PLASMA PHYSICS
    Type: NASA-CR-180176 , NAS 1.26:180176
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  • 8
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    Numerical tests of a modified full implicit continuous Eulerian (FICE) scheme with projected normal characteristic boundary conditions for MHD flows (1987)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A numerical method has been developed based on a modified full implicit continuous Eulerian (FICE) scheme and projected normal characteristic boundary conditions for simulating MHD flows which undergo a long process of evolution. An astrophysical flow is chosen for illustration of this procedure, and numerical tests are made to verify the computational stability and physically realistic solution. Three computational tests have been accomplished; they are tests of solving methods, characteristic boundary condition, and time steps. The tests show that the program from the modified FICE scheme with proper boundary conditions and time steps can be made numerically stable for a time long enough to obtain physically plausible solutions.
    Keywords: PLASMA PHYSICS
    Type: Computer Methods in Applied Mechanics and Engineering (ISSN 0045-7825); 64; 267-282
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  • 9
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    Amplification of electromagnetic waves by a ring-beam distribution of moderately relativistic electrons (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The possibility of a new mechanism for the excitation of unstable modes in cold background plasmas is indicated in this paper. These beam-cyclotron modes are excited by the presence of the ring-beam distribution of suprathermal electrons. The usual eigenmode excitation of a cold plasma is reviewed, and the new type of instability is examined using a single-harmonic approximation and multiharmonic treatment.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 29; 4212-421
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  • 10
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    Unstable-magnetic-drift waves in a plasma with temperature anisotropy (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: It is pointed out that under certain conditions, such as a weak electron temperature anisotropy, the magnetic-drift wave instability can become rather important, and the growth rate can be greater than the ion gyrofrequency when the scale length of the density gradient is comparable to, or shorter than, the thermal ion gyroradius. The instability is attributed to wave-electron interactions, and the growth rate is far greater than the case investigated by Krall and Rosenbluth (1963) who attributed the instability to wave-ion interactions. The anticipated vanishing of the instability is observed as epsilon sub n/epsilon sub B approaches zero. The presently observed instability may be used to explain the low-frequency fluctuations evidenced by the Active Particle Tracer Explorer Ion Release Module magnetometer measurements, and may contribute to the acceleration of ions along the plasma cometary tail.
    Keywords: PLASMA PHYSICS
    Type: Physics of Fluids (ISSN 0031-9171); 29; 1840-184
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