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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Hydrogen and helium excitation by EUV radiation for the production of white-light flares (1988)
    Springer
    Solar physics 115 (1988), S. 277-288 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract White-light flares are defined as those flares that produce significant enhancement of emission in the visible light continuum. The source of energy for this emission has not yet been identified with several possibilities being suggested: heating of the lower chromosphere by some mechanical or magnetic means, or by soft X-ray or extreme ultraviolet radiation from coronal loops being absorbed in the lower chromosphere and re-emitted in the visible. Using non-LTE radiative transfer calculations for hydrogen and helium in a simple model atmosphere we show that EUV (λ 〈 912 Å) radiation cannot be the main energy source for white-light flares. Estimates of the observed energy emitted in the visible and the EUV indicate that there may be enough energy in the EUV to account for the white light flare with this mechanism. Using enhancements in the wavelength region below 912 Å of up to ∼7 × 109 ergs cm−2 s−1 ster−1 (∼5 × 105 times the estimated q radiation field) to represent flare EUV emission from above we investigated the non-LTE level populations for hydrogen and helium and the lower atmospheric heating resulting from this radiation. The basic result is that the opacities in the Lyman continuum and the helium I and II continua are so much larger than even the enhanced opacity in the visible hydrogen continuum that the EUV radiation is absorbed before it can have a significant effect in the visible light continuum. However, the EUV radiation can cause a significant enhancement of Hα emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00148729
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  • 5
    Electronic Resource
    Electronic Resource
    The eruption of a quiescent prominence as observed in UV lines (1989)
    Springer
    Solar physics 123 (1989), S. 143-160 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We compare observations of an eruptive and a quiescent prominence in order to better understand the energetic processes in an eruptive prominence. Observations of an eruptive prominence were obtained in Hα, several UV emission lines (1215–1640 Å), and coronal white light at approximately 19:00 UT on September 20, 1980. The data we present shows the development of the eruption in the Hα and UV emission lines and is compared with the intensities from similar observations of a quiescent prominence. While the event is coincident with some coronal changes, above 1.2 and up to 1.5 solar radii, it does not result in a true coronal mass ejection event. The comparison between the eruptive and quiescent prominences reveals several differences which suggest that the activation consists not only of a mechanical movement of material, but also changes in the temperature of the prominence plasma. Some prominence material that does not seem to participate in the large scale prominence motion is heated during the eruptive event. Most of this material is heated to transition zone temperatures with almost no cool ‘core’ (i.e., no or very little Hα emission). The behavior indicates that there are structures that are first cool and then heat up to transition zone temperatures (apparently remaining stable for some time at these temperatures). Since this is an unstable temperature region for prominence type structures the energy transport that allows this is not understood and presents an interesting theoretical problem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150017
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  • 6
    Electronic Resource
    Electronic Resource
    The large coronal transient of 10 June 1973 (1975)
    Springer
    Solar physics 42 (1975), S. 163-177 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract During the 8.5 month flight of the High Altitude Observatory's white light coronagraph on board Skylab, over 100 coronal transients were observed. In this paper we present a description of one well observed loop transient, that of 10 June 1973. The transient apparently resulted from the eruption of a quiescent prominence on the limb; the emergence of a new, bipolar active region near the prominence may have caused the eruptior. The transient's leading edge rose from 3.6 to 5.0 solar radii (R ⊙) from Sun center at approximately 500 km s−1 during the 32 min of coronagraph observations. Material in a pre-existing streamer was swept away by the transient, causing the streamer to disappear. The mass ejected into the corona above a projected height of 2 R ⊙ was ≈ 5.4 × 1015 g, the potential energy associated with the ejected transient material was ⩾7.0 × 1030 erg, and the kinetic energy of the ejected material is estimated as 1.7 × 1030 erg. The 10 June 1973 transient was, in most respects, typical of other loop transients observed by Skylab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00153293
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  • 7
    Electronic Resource
    Electronic Resource
    FIRST RESULTS OF THE SUMER TELESCOPE AND SPECTROMETER ON SOHO – II. Imagery and Data Management (1997)
    Springer
    Solar physics 170 (1997), S. 105-122 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract SUMER – Solar Ultraviolet Measurements of Emitted Radiation – is not only an extreme ultraviolet (EUV) spectrometer capable of obtaining detailed spectra in the range from 500 to 1610 Å, but, using the telescope mechanisms, it also provides monochromatic images over the full solar disk and beyond, into the corona, with high spatial resolution. We report on some aspects of the observation programmes that have already led us to a new view of many aspects of the Sun, including quiet Sun, chromospheric and transition region network, coronal hole, polar plume, prominence and active region studies. After an introduction, where we compare the SUMER imaging capabilities to previous experiments in our wavelength range, we describe the results of tests performed in order to characterize and optimize the telescope under operational conditions. We find the spatial resolution to be 1.2 arc sec across the slit and 2 arc sec (2 detector pixels) along the slit. Resolution and sensitivity are adequate to provide details on the structure, physical properties, and evolution of several solar features which we then present. Finally some information is given on the data availability and the data management system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004994702333
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  • 8
    Electronic Resource
    Electronic Resource
    Mass flow in loop type coronal transients (1979)
    Springer
    Solar physics 61 (1979), S. 95-113 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The white light coronagraph on Skylab observed many loop type coronal transients. These loops travel through the coronagraph's field of view (2–6R ⊙) over a period of a few hours, after which the legs of the loops usually remain visible for a few days. In this paper we investigate the temporal changes in density and mass per unit length measured along the legs of such loops during the several days after the initial eruption. Examination of 8 transients shows that the mass and density in the legs decrease during the few hours after the top of the loop has travelled beyond the coronagraph's field of view. The mass and density then increase slowly, during the next one half to one day, then decrease again over approximately the same period. These changes are generally shown to be too rapid to be explained by solar rotation, indicating that the transient legs have a lifetime of only a few days. The results of a detailed study of the transient of 10 August 1973 are compared with the results from theoretical calculations. For the top of the loop a one-dimensional flow problem is solved, assuming a balance between gravity, inertia, and pressure gradients. The legs are modeled by a flow in a tube of constant cross section. Models for the flow in the legs were calculated under the assumption that the mass distribution is close to hydrostatic equilibrium. Using these models we can estimate that approximately 5 × 1014 g of material flow outward through the legs of this transient. We also find that the best fit to the observed average density gradient is obtained with a temperature of ∼1.7 × 106 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155449
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  • 9
    Electronic Resource
    Electronic Resource
    The association of coronal mass ejection transients with other forms of solar activity (1979)
    Springer
    Solar physics 61 (1979), S. 201-215 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Coronal mass ejection transients observed with the white light coronagraph on Skylab are found to be associated with several other forms of solar activity. There is a strong correlation between such mass ejection transients and chromospheric Hα activity, with three-quarters of the transients apparently originating in or near active regions. We infer that 40% of transients are associated with flares, 50% are associated with eruptive prominences solely (without flares), and more than 70% are associated with eruptive prominences or filament disappearances (with or without flares). Nine of ten flares which displayed apparent mass ejections of Hα-emitting material from the flare site could be associated with coronal transients. Within each class of activity, the more energetic events are more likely to be associated with an observable mass ejection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155456
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  • 10
    Electronic Resource
    Electronic Resource
    FIRST RESULTS OF THE SUMER TELESCOPE AND SPECTROMETER ON SOHO – I. Spectra and Spectroradiometry (1997)
    Springer
    Solar physics 170 (1997), S. 75-104 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract SUMER – the Solar Ultraviolet Measurements of the Emitted Radiation instrument on the Solar and Heliospheric Observatory (SOHO) – observed its first light on January 24, 1996, and subsequently obtained a detailed spectrum with detector B in the wavelength range from 660 to 1490 Å (in first order) inside and above the limb in the north polar coronal hole. Using detector A of the instrument, this range was later extended to 1610 Å. The second-order spectra of detectors A and B cover 330 to 805 Å and are superimposed on the first-order spectra. Many more features and areas of the Sun and their spectra have been observed since, including coronal holes, polar plumes and active regions. The atoms and ions emitting this radiation exist at temperatures below 2 × 106 K and are thus ideally suited to investigate the solar transition region where the temperature increases from chromospheric to coronal values. SUMER can also be operated in a manner such that it makes images or spectroheliograms of different sizes in selected spectral lines. A detailed line profile with spectral resolution elements between 22 and 45 mÅ is produced for each line at each spatial location along the slit. From the line width, intensity and wavelength position we are able to deduce temperature, density, and velocity of the emitting atoms and ions for each emission line and spatial element in the spectroheliogram. Because of the high spectral resolution and low noise of SUMER, we have been able to detect faint lines not previously observed and, in addition, to determine their spectral profiles. SUMER has already recorded over 2000 extreme ultraviolet emission lines and many identifications have been made on the disk and in the corona.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004923511980
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