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  • Other Sources  (10)
  • 1975-1979  (10)
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  • 1
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    Energy balance in a magnetically confined coronal structure observed by OSO-7 (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A model of a coronal region of enhanced Fe XV and Fe XVI emission is developed and its energy balance is examined using extreme ultraviolet observations from OSO-7 together with calculations of possible force-free coronal magnetic field configurations. The coronal emissions overlying the photospheric boundary between regions of opposite magnetic polarity are found to be associated with generally nonpotential (current-carrying) magnetic fields in the forms of arches with footpoints in regions of opposite polarity. The orientation of these arches relative to the neutral line changes with degree of ionization of the emitting ion (which we infer from our limb observations to be a function of height) and may be evidence of differing electric currents along various field lines. The appearance of a coronal arch, seen side-on, can conveniently be represented by a parabola and a detailed analysis shows this to be a realistic approximation that should be generally useful in analyzing two-dimensional pictures of coronal structures.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 43; Aug. 197
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  • 2
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    Numerical study of an explosion in a non-homogeneous medium with and without magnetic fields (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A version of the two step Lax-Wendroff difference method with second order accuracy is used to seek solutions of the unsteady magnetohydrodynamic (MHD) equations for the study of an explosion in a non-homogeneous medium with and without magnetic fields. The explosion is initiated by introducing a finite amount of energy in a small volume of gas which leads to an instantaneous increase of gas temperature. Two types of magnetic field configurations (i.e. open and closed) are considered to illustrate the dependence and differences of magnetic and a non-magnetic flow motion. Numerical results show the strong dependence of induced MHD flow field on the magnetic field configuration and strength. The development and decay of the fast and slow MHD shock waves, as well as the ordinary gasdynamic shock waves, are also represented well by the present computer simulations. In conclusion, we have demonstrated that the numerical scheme we have used is a reliable one for studying 2-dimensional MHD problems in non-homogeneous medium.
    Keywords: PLASMA PHYSICS
    Type: Computers and Fluids; 7; June 197
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  • 3
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    EUV emission, filament activation and magnetic fields in a slow-rise flare (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Results are reported for observations and analysis of synoptic data on a 1B flare that occurred on January 19, 1972. The observations include large-scale H-alpha movies of the flare and pre-flare developments, OSO-7 satellite data on soft X-ray and EUV developments, magnetograms, and hard X-ray observations. Theoretical force-free magnetic field configurations are compared with structures seen in the soft X-ray, EUV, and H-alpha images, and the evolution of the flare is described. The energy available for the flare is estimated from the change of magnetic field inferred from the H-alpha filtergrams and from force-free field calculations. It is suggested that the flare originated in a twisted filament where it was compressed by emerging fields, and it is shown that the flare started below the corona and appeared to derive its energy from the magnetic fields in or near the filament.
    Keywords: SOLAR PHYSICS
    Type: AD-A050171 , AFGL-TR-76-0021 , Solar Physics; 41; Apr. 197
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  • 4
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    Dynamic response of an isothermal static corona to finite-amplitude disturbances (1975)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Keywords: SOLAR PHYSICS
    Type: Solar Physics; 41; Apr. 197
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  • 5
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    Dynamical response of the solar corona. III - Numerical simulation of the 1973 June 10 coronal transient (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: A spherically symmetric adiabatic single-fluid model is outlined for simulating the nonlinear time-dependent response of the corona to solar events that are simulated by perturbations in the appropriate physical variables from their steady-state values at the coronal base. Several observed features of the coronal transient that occurred on June 10, 1973, are simulated by using a particular steady-state solar wind, a specific combination of density and temperature perturbations, and a particular time dependence of the perturbations. A different steady-state solar wind, a perturbation of shorter duration, and other perturbation combinations are also employed to simulate the same transient so that the effect of each quantity can be determined. It is found that the model cannot adequately simulate all the observational results for the investigated transient, that the steady-state solar wind is relatively unimportant in such numerical simulations, and that studies which attempt only to reproduce observed shock trajectories may lead to erroneous conclusions regarding the physics of the solar event that produced the transient.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 215
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  • 6
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    Magnetohydrodynamics of atmospheric transients. I - Basic results of two-dimensional plane analyses (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The dynamic behavior of transients in a stratified atmosphere in the presence of a magnetic field is investigated with the two-dimensional plane formulation, i.e., the formulation in which variations of the flow and magnetic field are confined within a plane. It is pointed out that, in the plane formulation, the noncompressible transverse waves (often called the Alfven waves) are excluded. The compressible responses of the atmosphere are then examined with a temperature perturbation (simulating a sudden local release of energy by a flare) as functions of the configuration of magnetic field and field strength. It is shown that (1) in the open (mostly radial) magnetic field, the propagation of 'bubble-like' density enhancements, the coronal transients, result; while (2) in the closed (mostly azimuthal) field, the density enhancement forms a pair of 'horns' near the foot points of field lines similar to that often observed by coronagraphs after flares. Discussions in interpreting the results in terms of the anisotropic propagation of the fast and slow waves (or shocks) are presented together with consideration of possible consequences with the inclusion of the transverse waves.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 219
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  • 7
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    Magnetohydrodynamics of atmospheric transients. II - Two-dimensional numerical results for a model solar corona (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: A systematic study of dynamic response of the inner solar corona is made within the context of two-dimensional, time-dependent plane hydromagnetics. The governing equations are written in r-phi coordinates (i.e., in the solar equatorial plane), and numerical solutions are obtained by introducing an impulsive temperature enhancement within a rectangular region (i.e., 'box') in an initially isothermal corona in magnetohydrostatic equilibrium. Effects of the magnetic field configuration are illustrated for initially open (radial) and closed (azimuthal) magnetic fields by comparison with the nonmagnetic response. The channeling or blocking effects by the magnetic fields on the mass motion of solar plasma as the consequence of the evolution of fast and slow mode MHD shock waves are demonstrated. Some physically significant applications of the results, useful for the interpretation of observations, are discussed. It is noted, for example, that coronal transients observed in white light probably occur within essentially radial field topologies.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal; vol. 219
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  • 8
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    On build-up of magnetic energy in the solar atmosphere (1976)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The dynamic response of the solar atmosphere is examined with the use of self-consistent numerical solutions to the complete set of nonlinear two-dimensional hydromagnetic equations. Of particular interest are the magnetic-energy buildup and the velocity field established by emerging flux at the base of an existing magnetic loop structure in a stationary atmosphere. For a plasma with a relatively low beta (0.03), the magnetic-energy buildup is approximately twice that of the kinetic energy, while the buildup in magnetic energy first exceeds but is eventually overtaken by the kinetic energy for a plasma with an intermediate beta (3). The increased magnetic flux causes the plasma to flow upward near the loop center and downward near the loop edges for the low-beta plasma. The plasma eventually flows downward throughout the lower portion of the loop carrying the magnetic field with it for the intermediate beta plasma. It is hypothesized that this latter case, and possibly the other case as well, may provide a reasonable simulation of the disappearance of prominences by flowing down into the chromosphere (a form of disparition brusque).
    Keywords: SOLAR PHYSICS
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  • 9
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    Global constant-alpha force-free magnetic fields and coronal structures (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Nakagawa's (1973) general formulation of constant-alpha global force-free magnetic fields is used to examine the topological characteristics of axisymmetric constant-alpha fields with specific reference to solar EUV, XUV, and X-ray structures observed from Skylab. The theoretical formulation is briefly summarized, and topological characteristics of the field lines are analyzed. The results are compared with X-ray observations of a large coronal arch and white-light observations of a coronal transient. It is concluded that global-scale force-free magnetic fields are present in the solar atmosphere and that their topological characteristics differ significantly from those of potential fields.
    Keywords: SOLAR PHYSICS
    Type: Astronomy and Astrophysics; 69; 1, Se; Sept
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  • 10
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    Dynamic modeling of coronal and interplanetary responses to solar events (1977)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Recent progress in the dynamic modeling of responses of the corona and interplanetary medium to solar events (such as surges, eruptive prominences, flares, etc.) is reviewed. In particular, coronal transients and wave phenomena are discussed in some detail including pertinent mathematical requirements. Within the context of hydrodynamics and magnetohydrodynamics, a summary of both one- and two-dimensional time-dependent models is presented. A comparison of theoretical results with ground-based optical, radio, ATM Skylab observations, Pioneer 9 and Pioneer 10 solar wind observations is also presented. It is illustrated that: (1) substantial progress has been made in the theoretical (i.e., numerical) modeling of coronal and interplanetary responses within the last few years; (2) two-dimensional, time-dependent modeling is needed to examine the details of nonlinear wave coupling; and (3) theoretical results of modeling appear to reproduce physical consequences successfully.
    Keywords: SOLAR PHYSICS
    Type: L. D. de Feiter Memorial Symposium; Jun 07, 1977 - Jun 10, 1977; Tel Aviv; Israel
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