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  • 1
    Electronic Resource
    Electronic Resource
    Relationships among flare images at different wavelengths (1982)
    Springer
    Solar physics 113 (1982), S. 67-86 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The talk reviews briefly historical development of the imaging of the Sun, and flare imaging in particular, at different wavelengths. The present state is then critically analyzed, emphasizing and demonstrating problems related to simultaneity of observed data, differences in time resolution, limitations of the imaged field of view, unequal spatial resolution, and alignment of the images. Prospects for the future are briefly sketched, including imaging in very hard X-rays and γ-rays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00147684
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Flaring arches (1988)
    Springer
    Solar physics 116 (1988), S. 91-118 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract ‘Flaring arches” is a name assigned to a particular component of some flares. This component consists of X-ray and Hα emission which traverses a coronal arch from one to the other of its chromospheric footpoints. The primary footpoint is at the site of a flare. The secondary footpoint, tens of thousands of kilometers distant from the source flare, but in the same active region, brightens in Hα concurrent with the beginning of the hard X-ray burst at the primary site. From the inferred travel time of the initial exciting agent we deduce that high speed electron streams travelling through the arch must be the source of the initial excitation at the secondary footpoint. Subsequently, a more slowly moving agent gradually enhances the arch first in X-rays and subsequently in Hα, starting at the primary footpoint and propagating along the arch trajectory. The plasma flow in Hα shows clearly that material is injected into the arch from the site of the primary footpoint and later on, at least in some events, a part of it is also falling back. Thus a typical flaring arch has three, and perhaps four consecutive phases: (1) An early phase characterized by the onset of hard X-ray burst and brightening of the secondary footpoint in Hα. (2) The main X-ray phase, during which X-ray emission propagates through the arch. (3) The main Hα phase, during which Hα emitting material propagates through the arch. And (4) an aftermath phase when some parts of the ejected material seem to flow in the reverse direction towards the primary site of injection. An extensive series of flaring arches was observed from 6 to 13 November, 1980 at the Big Bear Solar Observatory and with the Hard X-Ray Imaging Spectrometer (HXIS) on board the SMM in a magnetically complex active region. The two most intense arches for which complete Hα and X-ray data are available and which occurred on 6 November at 17 ∶ 21 UT (length ≈ 57000 km) and on 12 November at 16 ∶ 57 UT (length ≈ 263 000 km) are discussed in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00171717
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Flaring arches (1989)
    Springer
    Solar physics 123 (1989), S. 317-341 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss first the development of the coronal arch-shaped structure of ∼ 57000 km length which was born at or before 08:00 UT on 6 November, 1980 and became the site of 13 quasi-periodic brightenings in hard X-rays from 10:00 to 14:30 UT. The same structure became the site of a series of 17 flaring arches between 15:30 and 24:00 UT on that day. The periodicity of ∼ 19 min, defined well for the quasi-periodic variations, seems to be partly retained during the occurrence of the flaring arches. The flaring arch studied in Paper I (called SB arch) was the brightest event of this set of events. This paper presents its extended analysis and also an analysis of three other flaring arches that occurred in this configuration. All these events exhibit similar characteristics and thus demonstrate that the ‘flaring arch’ is a distinct solar phenomenon with specific characteristic properties. A comparison of Hα, Ov, and X-ray data for the SB arch essentially confirmed, in a quantitative way, the qualitative interpretation of the flow of emitting plasma through the arch proposed in Paper I. In particular, these data show: (1) a hot conduction front producing X-rays in the least dense plasma ahead, a decelerating more dense plasma bulk seen next in Ov, and still more decelerating very dense plasma eventually visible in emission in Hα; (2) a gradient of densities from the primary towards the secondary footpoint, by factor 3 in X-rays, one order of magnitude in Ov, and probably more in the densest loops emitting in Hα; (3) the secondary footpoint with hard X-ray spectrum, predominantly excited by particle streams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149109
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Multi-thermal observations of newly formed loops in a dynamic flare (1987)
    Springer
    Solar physics 108 (1987), S. 237-250 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The dynamic flare of 6 November, 1980 (max ≈ 15:26 UT) developed a rich system of growing loops which could be followed in Hα for 1.5 hr. Throughout the flare, these loops, near the limb, were seen in emission against the disk. Theoretical computations of deviations from LTE populations for a hydrogen atom reveal that this requires electron densities in the loops close to, or in excess of 1012 cm -3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 1012 cm -3 if no non-thermal motions were present, or 5 × 1011 cm -3 for a turbulent velocity of ~ 12 km s -1. It is now general knowledge that flare loops are initially observed in X-rays and become visible in Hα only after cooling. For such a high density, a loop would cool through radiation from 107 to 104 K within a few minutes so that the dense Hα loops should have heights very close to the heights of the X-ray loops. This, however, contradicts the observations obtained by the HXIS and FCS instruments on board SMM which show the X-ray loops at much higher altitudes than the loops in Hα. Therefore, we suggest that the density must have been significantly lower when the loops were formed and that the flare loops were apparently both shrinking and increasing in density while cooling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00214164
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Coronal mass ejection associated with the stationary post-flare arch of 21–22 May 1980 (1986)
    Springer
    Solar physics 103 (1986), S. 399-408 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract By using a combination of X-ray (HXIS), Hα (Haleakala), white-light corona (Solwind), and zodiacal light (Helios) images on 21–22 May, 1980 we demonstrate, and try to explain, the co-existence of a coronal mass ejection with a stationary post-flare coronal arch. The mass ejection was seen, both by Solwind and Helios, in prolongation of the path of a powerful spray, whereas the active region filament did not erupt. A tentative comparison is made with other occurrences of stationary, or quasi-stationary post-flare coronal arches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00147838
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Flaring arches (1982)
    Springer
    Solar physics 113 (1982), S. 303-304 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00147713
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    The footpoints of giant arches (1989)
    Springer
    Solar physics 124 (1989), S. 339-352 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have detected chromospheric footpoints of the giant post-flare coronal arches discovered by HXIS a few years ago. Hα photographs obtained at Big Bear and Udaipur Solar Observatories show chromospheric signatures associated with 5 sequential giant arch events observed in the interval from 6 to 10 November, 1980. The set of footpoints at one end of the arches consists of enhancements within a plage at the northeast periphery of the active region and the set of footpoints at the other end of the arch consists of brightenings of the chromosphere south of the active region. Both sets of footpoints show very slow brightness variations correlated in time with the brightness variations of the X-ray arches. Current-free modelling of the coronal magnetic field by Kopp and Poletto (1989), based on a Kitt Peak magnetogram, confirms the identification of the two sets of footpoints by showing magnetic field lines connecting them. The brightenings appear as a succession of point-like enhancements whose individual lifetimes are of the time-scale of minutes but which continue to occur for periods of several hours. This behaviour allows us to infer a fine structure in the coronal arches, undetectable in the X-ray images. The discovery of these brightenings and their location at the periphery of the active region also alters our conception of the relationship of the giant arches to the flares that begin concurrently with them. The giant arch phenomenon appears now to be either: (1) a long-lived, semi-permanent, coronal structure which is revived and fed with plasma and energy by underlying dynamic flares, or alternatively (2) a system of high-altitude loops which open at the onset of every such flare and subsequently reconnect over intervals of many hours.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156274
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