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  • SOLAR PHYSICS  (602)
  • 1985-1989  (278)
  • 1980-1984  (324)
  • 1
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    Solar wind-magnetosphere coupling and the distant magnetotail - ISEE-3 observations (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from absolute value of X = 120 to 140 R/sub e near the center of the tail to beyond absolute value of X = 200 R/sub e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B/sub z in the solar wind as observed by IMP-8. V/sub x in the distant plasma sheet is also found to be proportional to IMF B/sub z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 + or - 5 percent is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B/sub z and tailward V/sub x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.
    Keywords: SOLAR PHYSICS
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  • 2
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    Observations of a probable change in the solar radius between 1715 and 1979 (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: A decrease in the solar radius is determined using the technique of Dunham and Dunham (1973), in which timed observations are made just inside the path edges. When the method is applied to the solar eclipses of 1715, 1976, and 1979, the solar radius for 1715 is 0.34 + or - 0.2 arc second larger than the recent values, with no significant change between 1976 and 1979. The duration of totality is examined as a function of distance from the edges of the path. Corrections to the radius of the sun derived from observations of the 1976 and 1979 eclipses by the International Occultation Timing Association are also presented.
    Keywords: SOLAR PHYSICS
    Type: Science; 210; Dec. 12
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  • 3
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    Diode laser heterodyne observations of silicon monoxide in sunspots - A test of three sunspot models (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Absorption features from the 8 micron SiO fundamental (upsilon = 1-0) and hot bands (upsilon = 2-1) have been observed in sunspots at sub-Doppler resolution using a ground-based tunable diode laser heterodyne spectrometer. The observed line widths suggest an upper limit of 0.5 km/s for the microturbulent velocity in sunspot umbrae. Since the silicon monoxide abundance is very sensitive to sunspot temperature, the measured equivalent widths permit an unambiguous determination of the temperature-pressure relation in the upper layers of the umbral atmosphere. In the region of SiO line formation (log P sub g = 3.0-4.5), the results support the sunspot model suggested by Stellmacher and Wiehr (1970).
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 269; June 1
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  • 4
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    Solar wind-magnetosphere coupling and the distant magnetotail: ISEE-3 observations (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: ISEE-3 Geotail observations are used to investigate the relationship between the interplanetary magnetic field, substorm activity, and the distant magnetotail. Magnetic field and plasma observations are used to present evidence for the existence of a quasi-permanent, curved reconnection neutral line in the distant tail. The distance to the neutral line varies from absolute value of X = 120 to 140 R/sub e near the center of the tail to beyond absolute value of X = 200 R/sub e at the flanks. Downstream of the neutral line the plasma sheet magnetic field is shown to be negative and directly proportional to negative B/sub z in the solar wind as observed by IMP-8. V/sub x in the distant plasma sheet is also found to be proportional to IMF B/sub z with southward IMF producing the highest anti-solar flow velocities. A global dayside reconnection efficiency of 20 +- 5% is derived from the ISEE-3/IMP-8 magnetic field comparisons. Substorm activity, as measured by the AL index, produces enhanced negative B/sub z and tailward V/sub x in the distant plasma sheet in agreement with the basic predictions of the reconnection-based models of substorms. The rate of magnetic flux transfer out of the tail as a function of AL is found to be consistent with previous near-Earth studies. Similarly, the mass and energy fluxes carried by plasma sheet flow down the tail are consistent with theoretical mass and energy budgets for an open magnetosphere. In summary, the ISEE-3 Geotail observations appear to provide good support for reconnection models of solar wind-magnetosphere coupling and substorm energy rates.
    Keywords: SOLAR PHYSICS
    Type: DE86-002386 , LA-UR-85-3525 , CONF-850277-5 , NAS 1.15:88764 , NASA-TM-88764 , Chapman Conference on Solar Wind-magnetosphere Energy Coupling; Feb 12, 1985; Pasadena, CA; United States
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  • 5
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    Dynamical evolution of a solar coronal magnetic field arcade (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Calculations of the long-term dynamical evolution of a solar coronal magnetic field arcade which is subjected to shearing photospheric flows are presented. The evolution is obtained by numerical solution of a subset of the resistive magnetohydrodynamic equations. For a simplified model of the bipolar magnetic field observed in the solar corona, it is found that photospheric flow produces a slow evolution of the magnetic field, with a buildup of magnetic energy. For certain photospheric shear profiles, the field configuration produced is linearly unstable to an ideal magnetohydrodynamic mode when the shear exceeds a critical value. The nonlinear evolution of this instability shows the spontaneous formation of current sheets. Reconnection of the magnetic field produces a rapid release of magnetic energy. The major fraction of the energy is dissipated resistively, while a small fraction is converted into kinetic energy of an ejected plasmoid. The relevance of these results to two-ribbon flares is discussed.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 328; 830-847
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  • 6
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    A solar activity monitoring platform for SCADM (1980)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: The adaptation of proven space probe technology is proposed as a means of providing a solar activity monitoring platform which could be injected behind the Earth's orbital position to give 3 to 6 days advanced coverage of the solar phenomenon on the backside hemisphere before it rotates into view and affects terrestrial activities. The probe would provide some three dimensional discrimination within the ecliptic latitude. This relatively simple off-Earth probe could provide very high quality data to support the SCADM program, by transmitting both high resolution video data of the solar surface and such measurements of solar activity as particle, X-ray, ultraviolet, and radio emission fluxes. Topics covered include the orbit; constraints on the spacecraft; subsystems and their embodiments; optical imaging sensors and their operation; and the radiation-pressure attitude control system are described. The platform would be capable of mapping active regions on an hourly basis with one arc-second resolution.
    Keywords: SOLAR PHYSICS
    Type: NASA. Goddard Space Flight Center Study of the Solar Cycle from Space; p 45-54
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  • 7
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    Nonlinear radiative condensation in a sheared magnetic field (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A well-resolved two-dimensional nonlinear numerical simulation of the radiative/thermal instability in a sheared magnetic field is described which leads to filament formation. The condensation is initiated by a linearly unstable mode and widens until it is slowed by thermal conduction parallel to B. During the nonlinear evolution, the minimum temperature falls from 10 to the 6th K to 10 to the 4th K and eventually reaches a state of local thermal equilibrium in about five e-folding times.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 317; L91-L94
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  • 8
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    HRTS results from Spacelab 2 (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The High Resolution Telescope and Spectrograph (HRTS) instrument flew on the Spacelab 2 mission and consisted of a 30-cm Gregorian telescope, a slit spectrograph covering the 1190-1680 A region with 0.05-A spectral resolution, a broadband (90 A FWHM) spectroheliograph tuned to 1550 A, and an H-alpha filter system. The spectrograph slit was 920 arcsec, approximately in length. Subarcsecond spatial resolution along the slit is possible, but because of jitter in the Spacelab Instrument Pointing System, good exposures actually achieved 1-2 arcsec resolution.
    Keywords: SOLAR PHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 8, 19; 263-272
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  • 9
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    Highlights of the study of energy release in flares (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: From February 26 to March 1, 1979, 32 solar flare investigators attended a workshop at Cambridge, MA to define objectives and devise a scientific program for the study of energy release in flares (SERF) during the coming solar maximum. Herein, some major results of the ensuing five-year effort to observe and understand the flare energy release process and its effects (energetic particle production, coronal and chromospheric heating, electromagnetic radiations, and mass motions and ejections) are reviewed. The central issue - what processes store and release the energy liberated in flares - remains unresolved except in the most general terms (e.g., it is generally agreed that the energy is stored in sheared or stressed magnetic fields and released by field annihilation during some MHD instability). Resolving that issue is still one of the most important goals in solar physics, but the advances during the SERF program have brought it closer.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 114; 2, 19
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  • 10
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    Thermal bifurcation in the upper photosphere inferred from heterodyne spectroscopy of OH rotational lines (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Low-noise (S/N greater than 100), high spectral resolution observations of two pure rotation transitions of OH from the solar photosphere are used to make inferences concerning the thermal structure and inhomogeneity of the upper photosphere. It is found that the v = O R22(24.5)e line strengthens at the solar limb, in contradiction to the predictions of current one-dimensional photospheric models. The results for this line support a two-dimensional model in which horizontal thermal fluctuations in the upper photosphere are of the order plus or minus 800 K. This thermal bifurcation may be maintained by the presence of magnetic flux tubes and may be related to the solar limb extensions observed in the 30-200-micron region.
    Keywords: SOLAR PHYSICS
    Type: Solar Physics (ISSN 0038-0938); 94; 57-74
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