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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 152 (1994), S. 69-76 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The 1 Å index of the solar Ca II K line is compared with the core-to-wing ratio of satellite measurements of the Mg II h and k lines. The correlation coefficient r = 0.976 for the Nimbus-7 Mg II ratio during solar cycle 21 andr = 0.99 for the NOAA9 Mg II ratio in cycle 22. Linear regression analysis for the full dynamic range of both data sets is used to combine the Nimbus-7 and NOAA9 Mg II data. These relations permit the ground-based Ca K index to estimate the solar UV flux.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 66 (1980), S. 357-370 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Time sequences of profiles of the λ1548 line of C iv containing 51 EUV bursts observed in or near active regions are analyzed to determine the brightness, Doppler shift and line broadening characteristics of the bursts. The bursts have mean lifetimes of approximately 150s, and mean increases in brightness at burst maximum of four-fold as observed with a field of view of 2″ × 20″. Mean burst diameters are estimated to be 3″, or smaller. All but three of the bursts show Doppler shifts with velocities sometimes exceeding 75 km s−1; 31 are dominated by red shifts and 17 are dominated by blue shifts. Approximately half of the latter group have red-shifted precursors. We interpret the bursts as prominence material, such as surges and coronal rain, moving through the field of view of the spectrometer.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New center-to-limb measurements in FeI lines show changes in both the line profiles and the limb darkening curves that appear to be characteristic of many other solar lines. Here we seek the constraints placed on the atmospheric model by these effects. We find that in addition to a depth varying source function we must also allow the ratio of the continuous absorption coefficient to the total absorption coefficient to pass through a minimum in the mid-photosphere. Such an effect is consistent with inward increases of the Doppler width and damping constant in the upper photosphere and an inward increase of the ionization for both iron and hydrogen in the low photosphere.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 27 (1972), S. 27-33 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Bright emission arches in the spectra of Hα and the Ca II (H and K lines) are identified as the spectroscopic picture of the chromospheric network as it appears near the solar limb. Analysis of the geometrical properties of these spectroscopic arches indicates that the average network is a diverging sheet with a divergence angle of ∼ 50°. This sheet extends to 2600 km and 2000 km as an opaque emission feature in Hα and the Ca II (H and K) lines, respectively.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 39 (1974), S. 289-295 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe a tangential limb spectrum at 5870 Å which geometrically probes the high photosphere through the low chromosphere. Velocity and brightness structures with sizes ranging from 500 to 1500 km are present in the stronger emission lines. Such structure is consistent between the Fe i and Ba ii lines, and emission knots in these lines coincide with continuum bright streaks. But no correlation is evident between structure in the He i D3 line, emission in the Na i D2 line, and emission in the Fe i and Ba ii lines as a group. Two classes of near-horizontal velocity structure are seen in the height range from 0 to 500 km above the limb: υ ⪝ 1 km s−1 for the weaker metals and υ ∼ 7–10 km s−1 for the Na i line. Differences in line opacity are suggested as the cause of the low correlation between the fine structure in the various lines.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report high resolution measurements of the center-to-limb variation of the Mgi line at 4571.1 Å. This forbidden line is of interest because it should be formed in LTE. Comparison of our measurements with the Harvard-Smithsonian Reference Atmosphere show that the line center radiation originates in the temperature minimum region from 330 to 550 km above the point where τ continuum = 1. Observations near the limb confirm that the temperature minimum is ∼4200K.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 678-679 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] There are two possible explanations for why sunspots are dark: the partial suppression by the sunspot magnetic fields of convective energy transport from the underlying layers, or the removal of energy from the sunspot by enhanced hydromagnetic wave radiation. Both processes would reduce the ...
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 182 (1998), S. 97-105 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new instrument capable of 3-min time resolution full-disk and limb observations in the Hei 1083 nm spectral line has been in operation at the High Altitude Observatory's Mauna Loa Solar Observatory (MLSO) since April 1996. We discuss instrument capabilities and performance and present some initial observations of limb activity from the first year of instrument operation. We compare limb Hei and Hα observations of quiescent and active prominences, comment on the role of Doppler shifts in interpreting the Hei observations, and illustrate the use of disk/limb Hei observations of a CME-associated eruptive filament in mass-ejection studies.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 3 (1968), S. 269-281 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The discussion of the Hα double limb had reached the point where the question of its existence as a real solar phenomenon could not be resolved without new observations made with the Lockheed filter and the Mount Wilson spectroheliograph. A study of the instrumental profiles had indicated that there was sufficient off-band light to produce the observed inner limb step in the Mount Wilson instrument, but this analysis was not completely satisfactory because of limitations inherent in the measurement of instrument functions with a Hg-198 source. The instrumental profile work did indicate, however, that the spectral purity of the instruments in question could be substantially improved by the use of narrow-band interference filters. An experimental program was thus launched to determine the effect of such a blocking filter on the appearance of the Hα limb. The results of these observations with three Halle filter systems and the Mount Wilson spectroheliograph are that the inner limb completely disappears at the center of Hα when a blocking filter is used to reduce unwanted light, which originates at wavelengths beyond ±0.8 Å. In addition, the contrast and visibility of the chromospheric fine structure is increased by eliminating the off-band light. Thus the experiment conclusively demonstrates that the apparent inner limb is not a solar feature but is due entirely to instrumental parasitic light.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 3 (1968), S. 523-530 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new series of photometric observations of the H and K lines were obtained at Sacramento Peak Observatory in 1964 and 1965. In both the observations and the data reduction special attention was given to obtaining a suitable average over the solar fine structure and to defining a proper reference continuum. The results are that the central intensities of H and K are the same and equal to 4.2% of the continuum. The limb-darkening curves at the line centres are also the same for both lines.
    Type of Medium: Electronic Resource
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