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  • 1
    Digitale Medien
    Digitale Medien
    Coronal X-ray enhancements associated with Hα filament disappearances (1976)
    Springer
    Solar physics 48 (1976), S. 159-186 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A survey of soft X-ray images from Skylab has revealed a class of large-scale transient X-ray enhancements in the lower corona which are typically associated with the disappearance of Hα filaments away from active regions. Contemporary with the Hα filament disappearance, X-ray emitting structures appeared at or near the filament location with shape and size resembling the filament. Eventually these structures faded, but the filament cavity was no longer obvious. Typically the peak of the X-ray event lagged the end of the filament disappearance by tens of minutes. The durations of the coronal X-ray enhancements were considerably longer than the associated Hα filament disappearances. Major flare effects, such as chromospheric brightenings, typically were not associated with these X-ray events. One event analyzed quantitatively had a peak temperature between 1.8 and 2.7 × 106 K, achieved a peak density of ≈109 cm−3 and resulted in an enhancement in the plasma pressure over the conditions of the preexisting coronal cavity of at least a factor of 7. The mass of the coronal X-ray emitting material was about 10% that of the preexisting filament and the thermal energy of the coronal event was on the order of 1029 erg, about 10% of the mechanical energy of the Hα filament eruption. The event appeared to cool by radiative losses and not by thermal conduction. It is likely that the coronal enhancements are caused by heating of an excess of previously cooler material, either from the filament itself, or by compression of coronal material by a changing magnetic field.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00153342
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    X-ray and Hα observations of a filament-disappearance flare: An empirical analysis of the magnetic field configuration (1981)
    Springer
    Solar physics 70 (1981), S. 335-350 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A flare event occurred which involved the disappearance of a filament near central meridian on 29 August 1973. The event was well observed in X-rays with the AS & E telescope on Skylab and in Hα at BBSO. It was a four-ribbon flare involving both new and old magnetic inversion lines which were roughly parallel. The Hα, X-ray, and magnetic field data are used to deduce the magnetic polarities of the Hα brightenings at the footpoints of the brightest X-ray loops. These magnetic structures and the preflare history of the region are then used to argue that the event involved a reconnection of magnetic field lines rather than a brightening in place of pre-existing loops. The simultaneity of the Hα brightening onsets in the four ribbons and the apparent lack of an eruption of the filament are consistent with this interpretation. These observations are compared to other studies of filament disappearances. The preflare structures and the alignment of the early X-ray flare loops with the Hα filament are consistent with the schematic picture of a filament presented first by Canfield et al. (1974).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00151338
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Kinematical analysis of flare spray ejecta observed in the corona (1981)
    Springer
    Solar physics 73 (1981), S. 341-361 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The mass ejection event on 17 January 1974 was a classsic spray associated with a flare from an over the limb region. The structure of the accompanying coronal transient was typical of well-observed mass ejections, with coronal loops and a forerunner racing ahead of the rising prominence. Observations in Hα, soft X-ray, white light and radio wavelengths allowed us to track both cool (T e∼104 K) and hot (T e〉106 K) material from limb de-occultation to 6R ⊙. We determined the kinematics and thermodynamics of the internal material, and the overall mass and energy budget of the event. The majority of the mass and energy was linked with coronal material, but at least 20% of the ejected mass originated as near-surface prominence material. We conclude that the upper part of the prominence was being continuously heated to coronal temperatures as it rose through the corona. Above ∼2R ⊙ nearly all of the material was completely ionized. The primary acceleration of the prominence occurred below 3.5 × 104 km with all of the material exhibiting constant velocity above 1.5R ⊙. We found evidence that a moving type IV burst, indicative of strong magnetic fields, was associated with the upper part of the prominence. Our observations suggest that both the cool and hot material were acted upon by a similar, continuous force(s) to great heights and over a long time interval. We find that the observations are most consistent with magnetic propulsion models of coronal transients.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00151686
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    The spatial distribution of 6 centimeter gyroresonance emission from a flaring X-ray loop (1984)
    Springer
    Solar physics 92 (1984), S. 271-281 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We compare simultaneous high resolution soft X-ray and 6 cm images of the decay phase of an M3 X-ray flare in Hale Region 16413. The photographic X-ray images were obtained on an AS & E sounding rocket flown 7 November, 1979, and the 6 cm observations were made with the VLA. The X-ray images were converted to arrays of line-of-sight emission integrals and average temperature throughout the region. The X-ray flare structure consisted of a large loop system of length ∼ 1.3 arc min and average temperature ∼8 × 106 K. The peak 6 cm emission appeared to come from a region below the X-ray loop. The predicted 6 cm flux due to thermal bremsstrahlung calculated on the basis of the X-ray parameters along the loop was about an order of magnitude less than observed. We model the loop geometry to examine the expected gyroresonance absorption along the loop. We find that thermal gyroresonance emission requiring rather large azimuthal or radial field components, or nonthermal gyrosynchrotron emission involving continual acceleration of electrons can explain the observations. However, we cannot choose between these possibilities because of our poor knowledge of the loop magnetic field.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00157251
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    X-Ray and microwave observations of active regions (1983)
    Springer
    Solar physics 85 (1983), S. 267-283 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We compare coordinated, high spatial resolution (2–3 arc sec) observations at 6 cm and in soft X-rays with photospheric magnetograms and optical filtergrams of two active regions. The correspondence of the brightest centimetric components in these regions with coronal loops, sunspots and pores, chromospheric structures and the photospheric magnetic field was determined. Our principal results are: The association between the microwave components and coronal X-ray and photospheric magnetic field structures is complex; in general X-ray emission was not associated with the microwave components. A majority of the components were not associated with sunspots, although the brightest (T b ≥ 4 × 106 K) components overlay regions of strong photospheric field or high field gradients. Several of the components coincided with the apparent bases of shorter coronal loops and 4 with the tops of X-ray loops. The X-ray and magnetic field observations are used to constrain possible centimetric emission mechanisms. Thermal bremsstrahlung can not be a significant contributor to this bright microwave emission. Thermal gyro-resonance absorption is consistent with some of the observations, but untenable for those components which are bright in microwaves, lack X-ray emission, and overlie regions of weak magnetic field. As an explanation for the brightest (T b ≥ 4 × 106 K) components, the g-r theory requires coronal loops with significant currents but very low densities. Alternatively, a nonthermal mechanism implies that the emission arises from the transition region and suggests that discrete regions of continuous particle acceleration may be common in active regions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00148654
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Material ejection (1994)
    Springer
    Solar physics 153 (1994), S. 73-89 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract This paper reviews the major discussions and conclusions of the Flares 22 Workshop concerning the physical processes involved in mass ejecta events, with an emphasis on large-scale phenomena, especially Coronal Mass Ejections (CMEs). New insights have been gained from recent data obtained from the SMM andYohkoh spacecraft and from several new ground-based radio and optical instruments, as well as from theoretical advances concerning the origins, driving mechanisms and long-term evolution of CMEs.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00712493
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Book reviews (1996)
    Springer
    Solar physics 167 (1996), S. 453-453 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00146355
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Activity associated with the solar origin of coronal mass ejections (1987)
    Springer
    Solar physics 108 (1987), S. 383-401 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences and the proportions of association of all types of activity were similar. We also found a high percentage of association between SMM CMEs and X-ray long duration events (LDEs), in agreement with Skylab results. We conclude that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00214170
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    The correspondence between x-ray bright points and evolving magnetic features in the quiet sun (1993)
    Springer
    Solar physics 144 (1993), S. 15-35 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Coronal bright points, first identified as X-ray Bright Points (XBPs), are compact, short-lived and associated with small-scale, opposite polarity magnetic flux features. Previous studies have yielded contradictory results suggesting that XBPs are either primarily a signature of emerging flux in the quiet Sun, or of the disappearance of pre-existing flux. With the goal of improving our understanding of the evolution of the quiet Sun magnetic field, we present results of a study of more recent data on XBPs and small-scale evolving magnetic structures. The coordinated data set consists of X-ray images obtained during rocket flights on 15 August and 11 December, 1987, full-disk magnetograms obtained at the National Solar Observatory - Kitt Peak, and time-lapse magnetograms of multiple fields obtained at Big Bear Solar Observatory. We find that XBPs were more frequently associated with pre-existing magnetic features of opposite polarity which appeared to be cancelling than with emerging or new flux regions. Most young, emerging regions were not associated with XBPs. However, some XBPs were associated with older ephemeral regions, some of which were cancelling with existing network or intranetwork poles. Nearly all of the XBPs corresponded to opposite polarity magnetic features which wereconverging towards each other; some of these had not yet begun cancelling. We suggest that most XBPs form when converging flow brings oppositely directed field lines together, leading to reconnection and heating of the newly-formed loops in the low corona.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00667979
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    The association of nonthermal electrons with non-flaring coronal transients (1978)
    Springer
    Solar physics 57 (1978), S. 155-173 
    Details
    ISSN: 1573-093X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A close temporal and spatial association has been found between erupting filaments/coronal transients and radio noise storm continua. The three transients studied occurred away from active regions and are members of a class not usually accompanied by chromospheric emission. The data analyzed were from the S-054 soft X-ray telescope on Skylab and from one- and two-dimensional interferometers at meter and decameter wavelengths at Nançay and Clark Lake observatories. Calculations confirmed that observed microwave radiation from the transients is due to thermal bremsstrahlung. The results are consistent with an interpretation of heating of an increased amount of coronal plasma by nonthermal, 10–100 keV electrons. Three possibilities for the source of the material are described: (1) The filament material; (2) evaporation from the chromosphere or transition region; and (3) via a long-lived reconnection process.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00152052
    Standort Signatur Erwartet Verfügbarkeit
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