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  • Other Sources  (288)
  • SOLAR PHYSICS  (288)
  • 1990-1994  (288)
  • 1970-1974
  • 1990  (288)
  • 1
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    Sunspot seismology theory (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Physical mechanisms proposed to explain the absorption of significant p-mode wave power by sunspots are reviewed, and their viability in view of the current knowledge of the scattering process is discussed. It is concluded that there is no satisfactory theoretical model for the absorption of p-modes by sunspots available at present. It is argued that the resonance absorption model is able to obtain the large absorption coefficients observed for nonaxisymmetric perturbations. For axisymmetric perturbations, departures from perfect cylindrical symmetry or the inclusion of a slight twist in the sunspot flux tube may be able to resolve the problem with the absorption of m = 0 wave modes. Other dissipative models, which do not incorporate the background gradient effects inherent in the resonance absorption mechanism, require inconveniently large dissipation coefficients within the sunspot.
    Keywords: SOLAR PHYSICS
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  • 2
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    Global configuration of a magnetic cloud (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A magnetic cloud associated with a 2N flare on January 1, 1978 was observed by IMP-8, Helios A, Helios B, and Voyager 2. The variation of the magnetic field observed at each spacecraft is represented to good approximation by Lundquist's solution for a cylindrically symmetric force-free magnetic field with constant alpha. A least-squares fit of Lundquist's solution to the data from each spacecraft gives the local orientation of the axis of the magnetic cloud. The times of the estimated boundaries of the magnetic cloud at each spacecraft, together with the speeds of the boundaries and the spacecraft position, give the positions of the boundaries at a given time. From these results the magnetic cloud is determined to resemble a flux rope whose minor radius is approximately 0.15 AU at 1 AU, and whose radius of curvature at 1 AU is approximately 1/3 AU.
    Keywords: SOLAR PHYSICS
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  • 3
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    Resonant absorption of p-modes by sunspots (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Explanations for the observed p-mode absorption in sunspots are examined. It is demonstrated that any dissipative process like radiative, viscous, or resistive dissipation leads to the resonant absorption of acoustic waves incident on the sunspot tube, and that the resultant heating rate can be shown to be consistent with the observed absorption of the p-mode power impinging on an isolated inhomogeneously structured sunspot.
    Keywords: SOLAR PHYSICS
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  • 4
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    The Ulysses mission in the high latitude heliosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Ulysses, a joint ESA/NASA mission launched in October 1990, will be the first to explore the high latitude heliosphere. Launch will be from the Shuttle and a Jupiter gravity assist will be used to send the spacecraft first over the southern solar pole approximately three and one half years after launch and then over the northern solar pole one year later. Instruments will be carried to study the solar wind, the heliospheric magnetic field, energetic solar particles, galactic cosmic rays, solar X-rays, cosmic gamma rays, cosmic dust and interstellar neutral helium. The radio signals used to track and transmit spacecraft data will be used also to sound the corona and to search for gravitational waves.
    Keywords: SOLAR PHYSICS
    Type: In: Observatories in earth orbit and beyond (A93-23401 07-89); p. 307-313.
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  • 5
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    SOHO - An observatory to study the solar interior and the solar atmosphere (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Solar and Heliospheric Observatory (SOHO) is described. The two main objectives of SOHO are to improve understanding of solar coronal phenomena and to study solar structure and interior dynamics from its core to the photosphere. The primary goals of the coronal and solar wind studies are to understand the coronal heating mechanism and its expansion into the solar wind. These goals will be achieved both by remote sensing of the solar atmosphere with high resolution spectrometers and telescopes and by in situ measurement of the composition and energy of the resulting solar wind and the energetic particles that propagate through it. The structure and interior dynamics are to be studied by helioseismological methods and the measurement of solar irradiance variations. The SOHO spacecraft will be three-axis stabilized and located in a halo orbit around the L1 Lagrangian point (approximately 1 percent of the distance from the Earth to the Sun). It is currently scheduled for launch in July 1995.
    Keywords: SOLAR PHYSICS
    Type: In: Observatories in earth orbit and beyond (A93-23401 07-89); p. 277-284.
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  • 6
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    Solar accelerated particles - Comparisons of abundances and energy spectra from particle and gamma-ray observations (1990)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Gamma-ray observations of the April 27, 1981 flare have been used to derive elemental abundances of both the ambient gas and the accelerated particle which interact with this gas to produce gamma rays. The results show that the abundances of the accelerated particles which produce the gamma rays are much more consistent with first-class particle abundances than with large proton-flare abundances. Observed bremsstrahlung spectral from 16 flares are compared with calculated bremsstrahlung spectra. It is concluded that the electrons observed in interplanetary space and the electrons responsible for gamma-ray production cannot be drawn from the same accelerated particle population without the former being affected by reacceleration or energy-dependent escape.
    Keywords: SOLAR PHYSICS
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  • 7
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    Solar radiation on Mars (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Detailed information on solar radiation characteristics on Mars are necessary for effective design of future planned solar energy systems operating on the surface of Mars. Presented here is a procedure and solar radiation related data from which the diurnally, hourly and daily variation of the global, direct beam and diffuse insolation on Mars are calculated. The radiation data are based on measured optical depth of the Martian atmosphere derived from images taken of the sun with a special diode on the Viking cameras; and computation based on multiple wavelength and multiple scattering of the solar radiation.
    Keywords: SOLAR PHYSICS
    Type: Solar Energy (ISSN 0038-092X); 45; 6, 19; 353-363
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  • 8
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    The 155-day solar period in the sixteenth century and later (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Recent interest in short solar periods has been stimulated by the discovery of a peak period of about 150-160 days in very energetic solar flares and hard X-ray flares. Auroral data are used here as a proxy for solar activity to show the presence of the peak in data from 1570 to 1573 and in some other time periods. The data are also used to show the absence or lack of prominence of this peak at other times in the nineteenth and early twentieth centuries.
    Keywords: SOLAR PHYSICS
    Type: Nature (ISSN 0028-0836); 347; 365-367
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  • 9
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    An estimate of the maximum speed of the solar wind, 1938-1989 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In an effort to estimate the highest flow velocity that the solar wind has exhibited at earth during the past 50 years, geomagnetic storms that occurred from 1938 to 1989 were surveyed, and the storms that were preceded by a major proton flare were selected. For each identified flare-storm pair, the average speed ('transit speed') of the associated interplanetary shock from the interval between the flare onset and the sudden commencement of the geomagnetic storm was calculated. In each case, the maximum solar wind flow speed was inferred from an empirical relationship (derived for a sample of recent events) between the shock transit speed and the peak flow velocity of the associated transient stream, obtaining a distribution of maximum solar wind speeds, which presumably corresponds to a sample of the most energetic events of this 50-yr period. Results show no evidence for bulk flow velocities greater than the about 2000 km/sec value deduced by Zastenker et al. (1978) and Grunwaldt (1975) for the August 4, 1972 event.
    Keywords: SOLAR PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 17103-17
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  • 10
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    Quasilinear saturation of forced current sheet tearing modes (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Numerical studies of tearing modes in a nearly singular forced current sheet equilibrium (Liewer and Payne, 1990) show that the modes saturate quasilinearly when the width of the magnetic island formed by the reconnection is on the order of several times the linear mode width which scales as approximately (kS) exp -2/5, where S is the Lundquist number and k is the wavenumber. The modes saturate quasilinearly by flattening the current profile, converting magnetic energy into plasma energy. The longer wavelength modes, which saturate at higher levels, release the most energy. These modes may, nonlinearly, play a role in coronal heating when sharp current sheets form as a result of global magnetic stresses.
    Keywords: SOLAR PHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 17; 2047-205
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