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  • 1
    Electronic Resource
    Electronic Resource
    Temporal evolution of the equatorialK-corona (1977)
    Springer
    Solar physics 55 (1977), S. 143-159 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of the equatorialK-coronal radiance at 2.5R ⊙ from Sun center and its variation with time, on a daily basis, during the Skylab mission (May 1973–February 1974) are presented. The observations are subdivided into three periods, each characterized by a different variation of the radiance pattern with time. During the initial period, encompassing two solar rotations, there are several data gaps, but the radiance pattern shows a more or less smooth variation with time; however, during the second period (also about two solar rotations duration) the radiance signal is neither persistent on the short term nor recurrent from one limb passage to the next. Finally, during the last period, of five solar rotations duration, the radiance signal exhibits an orderly periodic behavior of increasing intensity. These results are interpreted as indicating a general simplification of the coronal magnetic field through the mission and, in comparison with harmonic analysis of the surface magnetic field (Levine, 1977), as indicating a rapid response of equatorial outer coronal structures to abrupt changes in the global surface field structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150881
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  • 2
    Electronic Resource
    Electronic Resource
    The relation between hard X-ray and transition-region line emission in solar flares (1985)
    Springer
    Solar physics 96 (1985), S. 317-330 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observational evidence suggests that both the hard X-ray and ultraviolet emission from the impulsive phase of flares result from an electron beam. We present the results of model calculations that are consistent with this theory. The impulsive phase is envisioned as occurring in many small magnetically confined loops, each of which maintains an electron beam for only a few seconds. This model successfully matches several observed aspects of the impulsive phase. The corona is heated to less than 2 × 106 K, maximum enhanced emission occurs in lines formed near 105 K, and there is only slight enhancement between 105 and 2 × 106 K. The slope of the observed relationship between hard X-ray and Ov 1371 Å emission is also matched, but the relative emission is not. The calculations indicate that UV emission lines formed below a temperature of about 105 K will arise predominantly from the chromospheric region heated by the electron beam to transition region temperatures. Emission lines formed at higher temperatures will be produced in the transition region. This should be detectable in density-sensitive line ratios. To account successfully for the impulsive UV emission, the peak temperature in the impulsively heated loops must remain below about 2 × 106 K. Thus our model implies that the impulsive heating takes place in different loops from the hotter gradual phase emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149687
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  • 3
    Electronic Resource
    Electronic Resource
    Energetics of a double flare on November 8, 1980 (1985)
    Springer
    Solar physics 98 (1985), S. 141-158 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Here we complete an energy balance analysis of a double impulsive hard X-ray flare. From spatial observations, we deduce both flares probably occur in the same loop within the resolution of the data. For the first flare, the energy in the fast electrons (assuming a thick-target model) is comparable to the convective up-flow energy, suggesting that these are related successive modes of energy storage and transfer. The total energy lost through radiation and conduction, 2.0 × 1028 erg, is comparable to the energy in fast electrons 2.5 × 1028 erg. For the second flare, the energy in the fast electrons is more than one order of magnitude greater than the energy of the convective up-flow. Total energy losses are within a factor of two lower than the calculated fast electron energy. We interpret the observations as showing that the first flare occurred in a small loop with fast electrons heating the chromosphere and resulting in chromospheric evaporation increasing the density in the loop. For the second flare most of the heating occurred at the electron acceleration site. The two symmetrical components of the Ca xix resonance line and a high velocity down-flow of 115 km s −1 observed at the end of the second hard X-ray burst are consistent with the flare eruption (reconnection) region being high in the flare loop. The estimated altitude of the acceleration site is 5500 km above the photosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00177204
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  • 4
    Electronic Resource
    Electronic Resource
    The scientific payload of the space-based Solar and Heliospheric Observatory (SOHO) (1994)
    Springer
    Space science reviews 70 (1994), S. 7-12 
    Details
    ISSN: 1572-9672
    Keywords: Solar Physics ; Solar Interior ; Solar Corona ; Solar Wind ; SOHO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The space-based Solar and Heliospheric Observatory (SOHO) is a joint venture of ESA and NASA within the frame of the Solar Terrestrial Science Programme (STSP), the first “Cornerstone” of ESA's long-term programme “Space Science — Horizon 2000”. The principal scientific objectives of the SOHO mission are: a) a better understanding of the structure and dynamics of the solar interior using techniques of helioseismology, and b) a better insight into the physical processes that form and heat the Sun's corona, maintain it and give rise to its acceleration into the solar wind. To achieve these goals, SOHO carries a payload consisting of 12 sets of complementary instruments which are briefly described here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00777835
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  • 5
    Electronic Resource
    Electronic Resource
    SOHO: The Solar and Heliospheric Observatory (1995)
    Springer
    Space science reviews 72 (1995), S. 81-84 
    Details
    ISSN: 1572-9672
    Keywords: solar physics ; solar interior ; solar corona ; solar wind ; SOHO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Solar and Heliospheric Observatory (SOHO), together with the Cluster mission, constitutes ESA's Solar Terrestrial Science Programme (STSP), the first “Cornerstone” of the Agency's long-term programme “Space Science — Horizon 2000”. STSP, which is being developed in a strong collaborative effort with NASA, will allow comprehensive studies to be made of the both the Sun's interior and its outer atmosphere, the acceleration and propagation of the solar wind and its interaction with the Earth. This paper gives a brief overview of one part of STSP, the SOHO mission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00768758
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  • 6
    Electronic Resource
    Electronic Resource
    SOHO operations and ground system (1994)
    Springer
    Space science reviews 70 (1994), S. 13-18 
    Details
    ISSN: 1572-9672
    Keywords: Sun ; Corona ; SOHO
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract SOHO is a joint ESA/NASA mission to study the sun from its interior to, and including, the solar wind in interplanetary space. It is currently scheduled for launch in 1995. After launch SOHO with be operated from the Experiment Operations Facility (EOF) at Goddard Space Flight Center (GSFC). The EOF will consist of facilities for instrument commanding, data reception, data reduction and data analysis. In this paper the operations concepts including instrument ground commanding from the EOF and communications capabilities between the EOF and ground observatories and the public networks in general will be described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00777836
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  • 7
    Electronic Resource
    Electronic Resource
    Frequency of coronal transients and solar activity (1976)
    Springer
    Solar physics 48 (1976), S. 127-135 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The High Altitude Observatory's white light coronagraph aboard Skylab observed some 110 coronal transients - rapid changes in appearance of the corona - during its 227 days of operation. The longitudes of the origins of these transients were not distributed uniformly around the solar surface (51 of the 100 events observed in seven solar rotations arose from a single quadrant of longitude). Further, the frequency of transient production from each segment of the solar surface was well correlated with the sunspot number and Ca ii plage (area × brightness) index in the segment, rotation by rotation. This correlation implies that transients occur more often above strong photospheric and chromospheric magnetic fields, that is, in regions where the coronal magnetic field is stronger and, perhaps, more variable. This pattern of occurrence is consistent with our belief that the forces propelling transient material outward are, primarily, magnetic. A quantitative relation between transient production from an area and the Zürich sunspot number appropriate to that area is derived, and we speculate that the relation is independent of phase in the solar activity cycle. If true, the Sun may give rise to as many as 100 white light coronal transients per month at solar cycle maximum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153339
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  • 8
    Electronic Resource
    Electronic Resource
    The speeds of coronal mass ejection events (1976)
    Springer
    Solar physics 48 (1976), S. 389-397 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The outward speeds of mass ejection events observed with the white light coronagraph experiment on Skylab varied over a range extending from less than 100 km s−1 to greater than 1200 km s−1. For all events the average speed within the field of view of the experiment (1.75 to 6 solar radii) was 470 km s−1. Typically, flare associated events (Importance 1 or greater) traveled faster (775 km s−1) than events associated with eruptive prominences (330 km s−1); no flare associated event had a speed less than 360 km s−1, and only one eruptive prominence associated event had a speed greater than 600 km s−1. Speeds versus height profiles for a limited number of events indicate that the leading edges of the ejecta move outward with constant or increasing speeds. Metric wavelength type II and IV radio bursts are associated only with events moving faster than about 400 km s−1; all but two events moving faster than 500 km −1 produced either a type II or IV radio burst or both. This suggests that the characteristic speed with which MHD signals propagate in the lower (1.1 to 3 solar radii) corona, where metric wavelength bursts are generated, is about 400 to 500 km s−1. The fact that the fastest mass ejection events are almost always associated with flares and with metric wavelength type II and IV radio bursts explains why major shock wave disturbances in the solar wind at 1 AU are most often associated with these forms of solar activity rather than with eruptive prominences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152004
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  • 9
    Electronic Resource
    Electronic Resource
    Coronal transients near sunspot maximum (1981)
    Springer
    Solar physics 69 (1981), S. 169-175 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Naval Research Laboratory's most recent Earth-orbiting coronagraph, called Solwind, has been observing the Sun's outer corona (2.6–10.0 R ⊙) at 10-min intervals since March 28, 1979. These observations provide the first comprehensive view of coronal transients near the peak of a sunspot cycle. Six, well-defined transients in our quick-look data have masses ranging from 7 × 1014 g to 2 × 1016 g and outward speeds ranging from 150 km s−1 to 900 km s−1. These values are comparable to the ones that were obtained with the OSO-7 and Skylab observations during the declining phase of the last sunspot cycle. Although the amount of quick-look data is not sufficient to provide meaningful statistics, the coronal transients near sunspot maximum seem to occur with a greater frequency and a wider latitude range than the transients during the declining phase of the cycle. In both eras, there is a good, but imperfect, association between the occurrence of coronal transients and surface phenomena such as eruptive prominences and flares.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151264
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  • 10
    Electronic Resource
    Electronic Resource
    Physical conditions in a quiescent prominence derived from UV spectra obtained with the UVSP instrument on the SMM (1983)
    Springer
    Solar physics 84 (1983), S. 63-70 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A quiescent prominence observed above the north-west limb on November 20, 1980, is analyzed using data obtained with the Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum Mission (SMM). The spectral data include the lines 1215 Å of Hi, 1401 Å of Oiv, 1402 Å of Siiv, 1548 Å of Civ, 1640 Å of Hei, and 1655 Å of Ci. From an analysis of these lines and their emission patterns we deduce physical characteristics of the prominence plasma, and suggest in particular that the prominence consisted of flux tubes at various temperatures. In the hotter parts of the plasma the number density reached values of about 3 × 1011 cm#X2212;3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00157443
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