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  • 1
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    Induced mass and wave motions in the lower solar atmosphere. I - Effects of shear motion of flux tubes (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations indicate that various dynamic solar phenomena lead to enhanced emission of electromagnetic waves from radio to X-ray wavelengths which can be traced to magnetic activity in the photospheric level. A number of previous investigations have ignored the dynamic responses in the solar atmosphere. On the other hand, Nakagawa et al. (1978, 1981) have studied the atmospheric responses in the frame of MHD in the supersonic super-Alfvenic region. Studies of the slowly varying dynamic response (subsonic) have been unsuccessful because of the requirements of high accuracy in the numerical scheme in which a rigorous mathematical treatment of the boundary conditions is necessary. Recently, a numerical MHD model was constructed by using the full implicit continuous eulerian method. The present investigation makes use of a method which is written in a more convenient numerical code. A two-dimensional, time-dependent, nonplanar MHD model is used to investigate the induced mass and wave motions in the lower solar atmosphere due to the shear motion of flux tubes.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 2
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    A mechanism for a class of solar coronal disturbances (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new ideal magnetohydrodynamic (MHD) model is used to examine the dynamical response of the upper solar atmosphere to the injection of cold mass from the photosphere, a surge perturbation. Theoretical results show that mass ejections from the photosphere will form loop structures with internally-moving plasma blobs, which is due to the mass injections from both legs in active regions leading to a reflection of waves at the top of the loop. The mass-loaded loop will remain as long as ejection continues, and will excite MHD waves propagating outward to the upper atmosphere, which may trigger a class of coronal disturbances.
    Keywords: SOLAR PHYSICS
    Type: Astrophysics and Space Science; 83; 1-2,; Apr. 198
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  • 3
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    Modeling of energy buildup for a flare-productive region (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A self-consistent MHD model of shearing magnetic loops is used to investigate magnetic energy buildup in active region AR 2372 (Boulder number), in the period of April 5-7, 1980. The magnetic field and sunspot motions in this region, derived using observational data obtained by the Marshall Space Flight Center Solar Observatory, suggest the initial boundary conditions for the model. It is found that the plasma parameters (i.e., density, temperature, and plasma flow velocity) do not change appreciably during the process of energy buildup as the magnetic loops are sheared. Thus, almost all of the added energy is stored in the magnetic field. Furthermore, it is shown that dynamical processes are not important during a slow buildup (i.e., for a shearing velocity less than 1 km/s). Finally, it is concluded that the amount of magnetic energy stored and the location of this stored magnetic energy depend on the initial magnetic field (whether potential or sheared) and the magnitude of the shearing motion.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 90; 117-131
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  • 4
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    Interaction between perpendicular magnetohydrodynamic shocks (1993)
    In:  Other Sources
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    Publication Date: 2019-08-14
    Description: A general analysis is made of the collision and merging of perpendicular shocks as well as the interaction between a shock and a tangential discontinuity. It is found that two head-on shocks diminish both in strength after collisions and a tangential discontinuity forms between them. The property of the discontinuity depends on the relative strength of the two shocks. No discontinuity occurs if the shocks are equal in strength. The emerging of two shocks propagating in the same direction results in a strong shock followed by a tangential discontinuity and a reverse wave. The reverse wave is a rarefaction wave if one or both of the shocks are strong. If the shocks are both weak, a critical adiabatic index (CAI) exists. The reverse wave is a rarefaction wave if the wavelength is less than the CAI and a shock exists if the wavelength is greater than the CAI. As a wake shock enters from a medium of higher wave impedance into that of lower wave impedance, the reflected wave is a rarefaction wave and the total pressure ratio decreases and the velocity jump increases after the shock passes through the border.
    Keywords: SOLAR PHYSICS
    Type: Physics of Fluids B (ISSN 0899-8221); 5; 3; p. 732-741.
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  • 5
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    Induced mass and wave motions in the lower solar atmosphere. II - Effects of converging and diverging photospheric motions (1986)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 306; 751-761
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  • 6
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    Double shock pairs in the solar wind (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: A numerical study of the evolution of a velocity enhancement disturbance in the solar wind is presented in terms of a 1D isentropic MHD flow model. It is shown that the disturbance steepens and evolves into a double shock pair while propagating outward away from the sun. The double shock pair consists of a reverse fast shock, a reverse slow shock, a forward slow shock, and a forward fast shock in order of distance away from the sun. The formation time of the double shock pair is nearly inversely proportional to the average velocity gradient of the disturbance. When the double shock pair is fully developed, the strength of the fast shocks is essentially determined by the disturbance amplitude, while the slow shocks behave differently. Their strength increases first with the disturbance amplitude but starts to decrease once the disturbance amplitude exceeds a certain value.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; A3; p. 3551-3561.
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