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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of Helically Twisted Prominence of January 22, 1979 (1998)
    Springer
    Astrophysics and space science 262 (1998), S. 29-38 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the dynamics of a macroscopically twisted helical prominence observed in Hα line on January 22, 1979 from Udaipur Solar Observatory. The analysis carried out is similar to that of March 11, 1979 event (Srivastava et al., 1991) wherein we had studied the role of twisted force-free magnetic fields in the prominence system. In the present study, it is found that of the two helically braided prominence tubes, one was dynamically more active. We have examined the temporal evolution of force-free parameter α, and the axial currents associated with the prominence system that decreased with time. We find that the magnitude of the electric currents and also the rate of energy release during the untwisting of the prominence was of comparatively higher order ∼ 1030 ergs s-1 than that of March 11, 1979 event, in agreement with the physical dimensions of the two prominences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001797601616
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Photospheric and Chromospheric Activity Associated with 3B Flare of February 27, 1992 (1998)
    Springer
    Astrophysics and space science 262 (1998), S. 363-374 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have analyzed the Hα filtergrams and vector magnetograms of the active region NOAA 7070, in which a 3B/X3.3 flare occurred on February 27, 1992. The average area per sunspot of this active region was in declining phase at the time of the flare. The vector magnetograms indicate that the magnetic field was non-potential at the flaring site. Besides non-potentiality, the longitudinal field gradient was found to be the highest at the region showing initial Hα brightening. Further, in Hα filtergrams no appreciable change in the morphology of the filament tracing the magnetic neutral line was noticed in the post-flare stage. Also, the photospheric vector magnetograms show considerable shear in post-flare magnetic field of the active region. In this paper we present the observations and discuss the possible mechanism responsible for the 3B/X3.3 flare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1001874701720
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Acceleration Profile of the Slow Solar Wind as Inferred from Gradual Mass Ejections Observed by LASCO (1999)
    Springer
    Space science reviews 87 (1999), S. 303-306 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The slow solar wind (〈 400 km s-1) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar wind from a distance of 1.1 up to 30 R⊙. We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several cases of gradual mass ejections and present them in perspective of earlier work.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005189610536
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  • 4
    Electronic Resource
    Electronic Resource
    On the Solar Origins of Intense Geomagnetic Storms Observed During 6–11 March 1993 (1998)
    Springer
    Solar physics 183 (1998), S. 419-434 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Intense geomagnetic storms with DST index ≤-100 nT were recorded on 9 March and 11 March 1993 associated with solar activity on 6 March and 9-10 March, respectively. In this paper, we discuss the characteristic features of the solar origins of the two events that gave rise to coronal and interplanetary disturbances and as a consequence produced strong geomagnetic activity at the Earth. The source of the activity in one case is attributed to a major 3M7.0 flare that occurred on 6 March 1993 and in the other case, to two large filament disruptions on the disk during 9-10 March, 1993. Both these sources were found to be located near changing or varying low-latitude coronal holes. They were also located close to the heliospheric currents sheets. Distinct X-ray activity was observed for both the events as observed by the Yohkoh SXT telescope. The detailed evolution and a comparison of these events on the basis of Yohkoh soft X-ray observations are presented here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005018328191
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    A Digital Imaging Multi-Slit Spectrograph for Measurement of Line-of-Sight Velocities on the sun (1999)
    Springer
    Solar physics 185 (1999), S. 61-68 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A multi-slit digital imaging spectrograph has been installed at Udaipur Solar Observatory, Udaipur (India) to measure the line-of-sight velocities in Hα associated with the mass motions of the dynamic phenomena on the solar surface viz. solar flares, eruptive prominences and surges. This spectrograph is being used in conjunction with a 15 cm aperture Coudé telescope to obtain the Hα spectra at a high rate of a specific region of interest on the Sun. In this paper, we describe the principal features of this instrument and the data acquisition method. We also present spectral observations of a surge and a quiescent prominence recorded using this instrument.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005189319845
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  • 6
    Electronic Resource
    Electronic Resource
    A possible explanation of reversed magnetic field features observed in NOAA AR 7321 (1995)
    Springer
    Solar physics 158 (1995), S. 249-258 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations of reversed-polarity features in the chromosphere as well as in the photosphere in the form of magnetic gulfs or islands of opposite polarity have been reported recently. In this paper, we present a possible explanation for the appearance of reversed-polarity features observed in the chromospheric magnetograms of the NOAA AR 7321 observed during October 25–27, 1992. It is suggested that the large-scale reversed-polarity features may occur due to the twisting of the smaller-scale magnetic flux tubes in the layer between the photosphere and the chromosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00795661
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