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  • 1
    Electronic Resource
    Electronic Resource
    Lasco Observations of Disconnected Magnetic Structures Out to Beyond 28 Solar Radii During Coronal Mass Ejections (1997)
    Springer
    Solar physics 175 (1997), S. 685-698 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two coronal mass ejections have been well observed by the LASCO coronagraphs to move out into the interplanetary medium as disconnected plasmoids. The first, on July 28, 1996, left the Sun above the west limb around 18:00 UT. As it moved out, a bright V-shaped structure was visible in the C2 coronagraph which moved into the field-of-view of C3 and could be observed out to beyond 28 solar radii. The derived average velocity in the plane of the sky was 110 ± 5 km s-1 out to 5 solar radii, and above 15 solar radii the velocity was 269 ± 10 km s-1. Thus there is evidence of some acceleration around 6 solar radii. The second event occurred on November 5, 1996 and left the west limb around 04:00 UT. The event had an average velocity in the plane of the sky of ∼54 km s-1 below 4 R⊙, and it accelerated rapidly around 5 R⊙ up to 310 ± 10 km s-1. In both events the rising plasmoid is connected back to the Sun by a straight, bright ray, which is probably a signature of a neutral sheet. In the November event there is evidence for multiple plasmoid ejections. The acceleration of the plasmoids around a projected altitude of 5 solar radii is probably a manifestation of the source surface of the solar wind.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004994214697
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  • 2
    Electronic Resource
    Electronic Resource
    Eit and LASCO Observations of the Initiation of a Coronal Mass Ejection (1997)
    Springer
    Solar physics 175 (1997), S. 601-612 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated to about 100 km s-1 and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at a velocity of 200–400 km s-1. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in the corona and here are shown to be present at the earliest stages of the CME. The event was later observed to traverse the LASCO coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest is the fact that this large-scale event, spanning as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5 x 104 km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated with this event as well as a considerable degree of activity near the west limb.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004907307376
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    First View of the Extended Green-Line Emission Corona At Solar Activity Minimum Using the Lasco-C1 Coronagraph on Soho (1997)
    Springer
    Solar physics 175 (1997), S. 667-684 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The newly developed C1 coronagraph as part of the Large-Angle Spectroscopic Coronagraph (LASCO) on board the SOHO spacecraft has been operating since January 29, 1996. We present observations obtained in the first three months of operation. The green-line emission corona can be made visible throughout the instrument's full field of view, i.e., from 1.1 R⊙ out to 3.2 R⊙ (measured from Sun center). Quantitative evaluations based on calibrations cannot yet be performed, but some basic signatures show up even now: (1) There are often bright and apparently closed loop systems centered at latitudes of 30° to 45° in both hemispheres. Their helmet-like extensions are bent towards the equatorial plane. Farther out, they merge into one large equatorial ‘streamer sheet’ clearly discernible out to 32 R⊙. (2) At mid latitudes a more diffuse pattern is usually visible, well separated from the high-latitude loops and with very pronounced variability. (3) All high-latitude structures remain stable on time scales of several days, and no signature of transient disruption of high-latitude streamers was observed in these early data. (4) Within the first 4 months of observation, only one single ‘fast’ feature was observed moving outward at a speed of 70 km s-1 close to the equator. Faster events may have escaped attention because of data gaps. (5) The centers of high-latitude loops are usually found at the positions of magnetic neutral lines in photospheric magnetograms. The large-scale streamer structure follows the magnetic pattern fairly precisely. Based on our observations we conclude that the shape and stability of the heliospheric current sheet at solar activity minimum are probably due to high-latitude streamers rather than to the near-equatorial activity belt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004948913883
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  • 4
    Electronic Resource
    Electronic Resource
    SOHO ground segment, science operations, and data products (1995)
    Springer
    Solar physics 162 (1995), S. 39-59 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe the ground segment, pre-launch operations concepts, and data products supporting the SOHO mission. Our goal is threefold: first, we provide a historical view of the design and development of the systems described here, as a background perspective to those who will use the system and those who may build such systems for future missions. Second, because we hope that many researchers from the solar and space physics communities will visit these facilities during the mission, we provide an overview for the benefit of the end-user. We anticipate that visitors to GSFC may plan observations for one or more of SOHO's complement of instruments, and such researchers may use the facilities to analyze data gathered by the SOHO instruments. Third, we present the working plan for investigators with groundbased or other spacebased instruments to collaborate with SOHO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733426
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  • 5
    Electronic Resource
    Electronic Resource
    The Relationship of Green-Line Transients to White-Light Coronal Mass Ejections (1997)
    Springer
    Solar physics 175 (1997), S. 699-718 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report observations by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft of three coronal green-line transients that could be clearly associated with coronal mass ejections (CMEs) detected in Thomson-scattered white light. Two of these events, with speeds 〉25 km s-1, may be classified as ‘whip-like’ transients. They are associated with the core of the white-light CMEs, identified with erupting prominence material, rather than with the leading edge of the CMEs. The third green-line transient has a markedly different appearance and is more gradual than the other two, with a projected outward speed 〈10 km s-1. This event corresponds to the leading edge of a ‘streamer blowout’ type of CME. A dark void is left behind in the emission-line corona following each of the fast eruptions. Both fast emission-line transients start off as a loop structure rising up from close to the solar surface. We suggest that the driving mechanism for these events may be the emergence of new bipolar magnetic regions on the surface of the Sun, which destabilize the ambient corona and cause an eruption. The possible relationship of these events to recent X-ray observations of CMEs is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004981125702
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  • 6
    Electronic Resource
    Electronic Resource
    Activity associated with coronal mass ejections at solar minimum: SMM observations from 1984–1986 (1991)
    Springer
    Solar physics 136 (1991), S. 379-394 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have examined 73 coronal mass ejections observed by the coronagraph aboard NASA's Solar Maximum Mission between 1984–1986. The goal of this study was to determine the distribution of various forms of solar activity that were spatially and temporally associated with mass ejections during solar minimum phase. For each coronal mass ejection a speed could be measured, hence, we were able to estimate a departure time of the transient from the lower corona. We then searched for other forms of solar activity that appeared within 45° longitude and 30° latitude of the mass ejection and within ± 90 minutes of its extrapolated departure time. We present the statistical results of the analysis of these 73 mass ejections, and we found that slightly less than half of the mass ejections had associations. This fraction is lower than reported by similar previous studies of Skylab and SMM 1980 coronagraph observations. We attribute the lower association rate to the large fraction of slow mass ejections detected during 1984–1986. Taken as a group, the slow mass ejections were infrequently associated with other forms of solar activity. This is the first such study to examine the association problem near the minimum phase of solar activity, but our results indicate that the distribution of the various forms of activity related to mass ejections does not appear to change at different phases of the solar cycle. For those CMEs with associations we found that eruptive prominences and soft X-ray events (especially long-decay events) were the most likely forms of activity to accompany the appearance of mass ejections. Our result strengthens the interpretation that most coronal mass ejections are the result of the reconfiguration of a magnetic field structure surrounding a prominence, leading to the destabilization and eruption of the prominence and its overlying coronal structure. This phenomenon occurs in both quiescent prominences and in prominences found in active regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146543
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