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  • 1
    Electronic Resource
    Electronic Resource
    The extended solar activity cycle (1988)
    [s.l.] : Nature Publishing Group
    Nature 333 (1988), S. 748-750 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The small overlap of successive sunspot cycles in the butterfly diagram has long been known. But during the 1950s, coronal observers1'3 noted that, in addition to the strong maxima in the emission of the 5,303-A wavelength (green) line at sunspot latitudes, a zone of enhanced emission appears at ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/333748a0
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  • 2
    Electronic Resource
    Electronic Resource
    Large-scale coronal heating by the small-scale magnetic field of the Sun (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 394 (1998), S. 152-154 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Magnetic fields play a crucial role in heating the outer atmospheres of the Sun and Sun-like stars, but the mechanisms by which magnetic energy in the photosphere is converted to thermal energy in the corona remain unclear. Observations show that magnetic fields emerge onto the solar surface as ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/28108
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  • 3
    Electronic Resource
    Electronic Resource
    Observations of coronal structure during sunspot maximum (1982)
    Springer
    Space science reviews 33 (1982), S. 219-231 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents some of the results that have been obtained from the Kitt Peak observations of coronal holes and the NRL observations of coronal transients during the recent years near sunspot maximum (1979–1981). On the average, low-latitude coronal holes of comparable size contained 3 times more flux near sunspot maximum than near the previous minimum. In the outer corona, transients occurred at the observed rate of at least 2 per day, and quiet conditions persisted during less than 15 % of the observed days. We describe a sample of the more than 800 events that we have observed so far, including the observation of a comet apparently colliding with the Sun.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00213255
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  • 4
    Electronic Resource
    Electronic Resource
    X-ray bright points and He i λ 10830 dark points (1989)
    Springer
    Solar physics 124 (1989), S. 211-217 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using near-simultaneous full disk solar X-ray images and Hei λ10830 spectroheliograms from three rocket flights, we compare dark points identified on the Hei maps with X-ray bright points identified on the X-ray images. We find that for the largest and most obvious features there is a strong correlation: most Hei dark points correspond to X-ray bright points. However, about two-thirds of the X-ray bright points were not identified on the basis of the helium data alone. Once an X-ray feature is identified it is almost always possible to find an underlying dark patch of enhanced Hei absorption which, however, would not a priori have been selected as a dark point. Therefore, the Hei dark points, using current selection criteria, cannot be used as a one-to-one proxy for the X-ray data. Hei dark points do, however, identify the locations of the stronger X-ray bright points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156266
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  • 5
    Electronic Resource
    Electronic Resource
    Ephemeral active regions in 1970 and 1973 (1975)
    Springer
    Solar physics 40 (1975), S. 87-102 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study of ephemeral active regions (ER) identified on good quality full-disk magnetograms reveals: (1) On the average 373 and 179 ER were present on the Sun in 1970 and 1973 respectively. The number varies with the solar cycle. (2) The median lifetime of ER depends on observation quality and selection rules but is estimated as about 12 hr for our data. (3) The latitude distribution is very broad but not uniform. The distribution peaks near the equator and shows variations similar to distributions of large active regions. (4) The longitude distribution is essentially homogeneous. (5) The spatial orientation of ER is almost random. In 1973 there is a hint of an excess of new cycle orientations at high latitudes. A comparison of parameters of ER and regular active regions suggests that ER are the small-scale end of a broad spectrum of active regions. The role of ER in the light of present theories of solar activity is investigated but is not yet clear. Heating of the chromosphere and corona may be significantly affected by ER.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00183154
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  • 6
    Electronic Resource
    Electronic Resource
    Simulations of magnetic-flux transport in solar active regions (1985)
    Springer
    Solar physics 102 (1985), S. 41-49 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We simulate the evolution of several observed solar active regions by solving a transport equation for magnetic flux at the photosphere. The rates of rotation, meridional flow, and diffusion of the flux are determined self-consistently in the calculations. Our findings are in good quantitative agreement with previous measures of the rotation rate and diffusion constant associated with photospheric magnetic fields. Although our meridional velocities are consistent in direction and magnitude with recently reported poleward flows, relatively large uncertainties in our velocity determinations make this result inconclusive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154036
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  • 7
    Electronic Resource
    Electronic Resource
    A study of the magnetic and velocity fields in an active region (1976)
    Springer
    Solar physics 47 (1976), S. 233-246 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A time sequence of magnetograms and velocity-grams in the Hα and Fe i 6569 Å lines has been made at a rate of 12 h−1 of McMath Region 10385 from 26 to 29 October, 1969. The 14 flares observed during this period have been studied in relation to the configuration and changes in the magnetic and velocity fields. There was little correlation between flare position and the evolutionary changes in the photospheric magnetic and velocity field, except at large central meridian distances where the velocity observations suggested shearing taking place at flare locations. At central meridian distances 〉 30° we found that flares are located in areas of low line-of-sight photospheric velocity surrounded by higher velocity hills. The one exception to this was the only flare which produced a surge. Blue-shifted velocity changes in the photosphere of 0.3 to 1 km s−1 were observed in localized areas at the times of 8 of 14 flares studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152261
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic measurements of coronal holes during 1975–1980 (1982)
    Springer
    Solar physics 79 (1982), S. 149-160 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photospheric magnetic fluxes and average field strengths have been measured beneath 33 coronal holes observed on 63 occasions during 1975–1980. The principal result is that low-latitude holes contained 3 times more flux near sunspot maximum than near minimum despite the fact that their sizes were essentially the same. Average magnetic field strengths ranged from 3–36 G near sunspot maximum compared to 1–7 G near minimum. Evidently the low-latitude coronal holes received a proportion of the extra flux that was available at low latitudes near sunspot maximum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146979
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  • 9
    Electronic Resource
    Electronic Resource
    The photospheric magnetic flux budget (1994)
    Springer
    Solar physics 150 (1994), S. 1-18 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ensemble of bipolar regions and the magnetic network both contain a substantial and strongly variable part of the photospheric magnetic flux at any phase in the solar cycle. The time-dependent distribution of the magnetic flux over and within these components reflects the action of the dynamo operating in the solar interior. We perform a quantitative comparison of the flux emerging in the ensemble of magnetic bipoles with the observed flux content of the solar photosphere. We discuss the photospheric flux budget in terms of flux appearance and disappearance, and argue that a nonlinear dependence exists between the flux present in the photosphere and the rate of flux appearance and disappearance. In this context, we discuss the problem of making quantitative statements about dynamos in cool stars other than the Sun.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712873
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