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  • 1
    Electronic Resource
    Electronic Resource
    The chromospheric network: Dependence of cell lifetime on length-scale (1999)
    Springer
    Solar physics 184 (1999), S. 267-280 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A time series of Ca ii K filtergrams of the chromosphere was used to study the relationship between correlation lifetimes and autocorrelation length scales. The form of the lifetime-scale relation is inferred by comparing the distribution of the two parameters. A linear dependence of lifetime on cell area, with a least squares fit slope of 3.34×107 km2 hr−1, is deduced. The relation can be explained by assuming the network evolves by means of a diffusion process of the magnetic elements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005125326765
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  • 2
    Electronic Resource
    Electronic Resource
    Short-period intensity oscillations in the solar corona observed during the total solar eclipse of 26 February 1998 (1999)
    Springer
    Solar physics 188 (1999), S. 89-98 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Encouraged by the detection of high-frequency, low-amplitude continuum intensity oscillations in the solar corona during the total solar eclipse of 1995, we designed and fabricated a six-channel photometer incorporating low-noise Hamamatsu R647 photomultipliers. Fast photometry at five different locations in the solar corona was performed at Don Bosco Mission, Venezuela during the total solar eclipse of 26 February 1998. Three interference filters with passbands of about 150 Å and centered around 4700, 4900, and 5000 Å were used. The photometric data were recorded at a rate of 20 Hz in three channels and 50 Hz in the remaining three channels. The power spectrum analysis of one of the channels that recorded appreciable counts indicates the existence of intensity oscillations in the frequency range 0.01–0.2 Hz. A least-squares analysis yields 90.1, 25.2, and 6.9 s periods for the three prominent components which have amplitudes in the range 0.5–3.5% of the coronal brightness. These periods and their amplitudes are similar to those detected in the coronal intensity oscillations during the 1995 eclipse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005149303094
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  • 3
    Electronic Resource
    Electronic Resource
    The Dependence of Chromospheric Ca II K Network Cell Sizes on Solar Latitude (1998)
    Springer
    Solar physics 180 (1998), S. 47-51 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Calcium K line spectroheliograms obtained during the solar minimum phases at Kodaikanal between 1913–1974 have been used to study the network cell sizes. The autocorrelation is calculated for two-dimensional strips at 5° interval up to ±50° latitude. The average size of the network cells was found to have a dependence on solar latitude with a maximum variation of about 7%. The pattern shows an apparent north–south symmetry with two minima at about 20° N and S.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005072907000
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  • 4
    Electronic Resource
    Electronic Resource
    Clues to the mode of excitation of Fe x ions in the solar corona from the 1980 eclipse observations (1985)
    Springer
    Solar physics 95 (1985), S. 253-262 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The line and continuum intensities deduced from the multislit spectra of the (Fe X) coronal emission line taken at the 1980 eclipse are used to discuss the relative roles of radiative and collisional excitation mechanisms. It is shown that for R/R ⊙ 〈 1.2, collisional excitation is the predominant mode. Collisional as well as radiative excitation is equally important for 1.2 〈 R/R ⊙ 〈 1.4, whereas beyond 1.4 R ⊙ radiative excitation becomes dominant. The line width measurements indicate that a large number of locations have half-widths around 1.3 Å. The maximum half-width is reached at ∼ 1.4 R ⊙ with an average value of 1.6 Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152403
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  • 5
    Electronic Resource
    Electronic Resource
    Variations in the solar rotation rate derived from Ca+ K plage areas (1985)
    Springer
    Solar physics 97 (1985), S. 203-212 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Daily calcium plage areas for the period 1951–1981 (which include the solar cycle 19 and 20) have been used to derive the rotation period of the Sun at latitude belts 10–15 ° N, 15–20 ° N, 10–15 ° S, and 15–20 ° S and also for the entire visible solar disk. The mean rotation periods derived from 10–20 ° S and N, total active area and sunspot numbers were 27.5, 27.9, and 27.8 days (synodic), respectively. A power spectral analysis of the derived rotation rate as a function of time indicates that the rotation rate in each latitude belt varies over time scales ranging from the solar activity cycle, down to about 2 years. Variations in adjacent latitude belts are in phase, whereas those in different hemispheres are not correlated. The rotation rates derived from sunspot numbers also behave similarly though the dependence over the solar cycle are not very apparent. The total plage areas, integrated over the entire visible hemisphere of the Sun shows a dominant periodicity of 7 years in rotation rate, while the other time scales are also discernible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152989
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  • 6
    Electronic Resource
    Electronic Resource
    The Correlation Lifetimes of Chromospheric Ca II K Network Cells (1998)
    Springer
    Solar physics 178 (1998), S. 251-257 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The lifetimes and spatial scales of emission network cells in the solar chromosphere were studied from a nearly continuous sequence of Caii K filtergrams, obtained from Antarctica. The temporal autocorrelation function (ACF) was calculated for spatially-aligned windows from the time sequence of filtergrams. The lifetime of network cells was found to be dependent on the activity of the region. The estimated lifetimes are 24–34 hours for quiet-region cells and 58–61 hours for active-region cells. The temporal ACF shows prominent undulations in some of the quiet-region windows. The spatial ACF reveals the periodicity of the emission network in quiet regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005094523212
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  • 7
    Electronic Resource
    Electronic Resource
    The Chromospheric Network – (A) Network Evolution Viewed as a Diffusion Process (1999)
    Springer
    Solar physics 187 (1999), S. 1-9 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Autocorrelation and cross-correlation techniques have been applied to obtain quantitative information about the dynamics of magnetic flux on the solar surface. The speed of network magnetic elements and the diffusion coefficient associated with their random motion is derived. The speed is found to be about 0.1 km s−1, independent of activity level. However, the diffusion coefficient shows a strong activity dependence: it is about 370–500 km2 s−1in the quiet network and 135–210 km2 s−1in the enhanced network. It is found that the lifetime of the enhanced network relative to the quiet network is compatible with that suggested by a comparison of their respective diffusion coefficients. This supports the proposition that a diffusion-like dispersion of magnetic flux is the dominant factor in the large-scale, long-term evolution of the network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005168001758
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  • 8
    Electronic Resource
    Electronic Resource
    Spatio-temporal fluctuations in HeI 10830 Å line parameters: Evidence for spicule formation (1992)
    Springer
    Solar physics 138 (1992), S. 107-121 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The equivalent width, line depth, line width, and Doppler shift of the He i 10830 Å line were extracted from two time series of spectra. Scatter plots of time-averaged line depth, line width, and Doppler shifts, as well as the root mean square temporal fluctuation of these quantities against the time-averaged equivalent width at a few hundred spatial locations were obtained. The statistical behaviour of these line parameters and their fluctuations was used to infer plausible reasons for the fluctuations. Examination of these results showed that the line parameter fluctuations could be caused by fluctuations in the coronal UV radiation (which could drive the spicules) or by the appearance of density inhomogeneities such as spicules within the line forming domain. In either case, the data can be interpreted as representing the initial phases of spicules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146199
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  • 9
    Electronic Resource
    Electronic Resource
    On the eruption of prominences and disappearance of quiescent filaments (1995)
    Springer
    Solar physics 158 (1995), S. 259-268 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We suggest the following heuristic model for the evolution of a quiescent filament. The middle part of the filament rises due to heating, while its ends remain anchored in the chromosphere; and a kink appears in the Hα filament due to projection and line-of-sight effects. Further, the top segment of the filament rises rapidly above the solar surface 1–2 days before the disappearance of a filament or eruption of a prominence. The top of the filament attains a high temperature due to further heating, thereby becoming invisible in Hα, giving the impression that the filament has split into two parts. It is expected that this gap between the Hα filament can be seen in the observations in high-temperature lines and soft X-rays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00795662
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  • 10
    Electronic Resource
    Electronic Resource
    Sun as a star: Rotation rates from the Ca K-index (1987)
    Springer
    Solar physics 109 (1987), S. 387-391 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Daily measurements for 18 months made at Tucson of the Ca K-index in integrated sunlight have been used to derive solar rotation rates. Power spectral analysis shows that one can obtain a well defined value of solar rotation rate in a period of six months, provided the data are fairly continuous. One might suppose it is possible to study the variation of solar (or stellar) rotation rate with time, a variation arising from a combination of differential rotation and shifts in the active latitude. A comparison between our observed rates and the prevailing dominant activity zones does not support this supposition, at least for the interval studied. Rather, our rates seem to depend on the circumstances of sampling and active region birth and decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160661
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