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  • 11
    Electronic Resource
    Electronic Resource
    Coronal hole flux tubes and the problem of relating interplanetary and solar features (1996)
    Springer
    Astrophysics and space science 243 (1996), S. 113-121 
    Details
    ISSN: 1572-946X
    Keywords: Coronal holes ; Solar wind sources
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Coronal flux tubes have in general very large divergence, and the properties of their flow vary greatly inside the flux tube. We present here a general description of the evolution and the characteristics of coronal holes and discuss how these characteristics may lead to erroneous associations, between interplanetary and solar structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00644040
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  • 12
    Electronic Resource
    Electronic Resource
    Coronal magnetic structures associated with interplanetary clouds (1999)
    Springer
    Solar physics 188 (1999), S. 163-168 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Among all the signatures of solar ejecta in interplanetary space, magnetic clouds are particularly interesting. We have shown that they are associated with solar mass ejections that involve not only coronal heights, but also chromospheric heights and so, they are almost always associated with low-altitude solar activity such as Hα flares or filament eruptions. As a magnetic cloud is a very large structure, and not all the ejecta found in the interplanetary medium are clouds, it is interesting to investigate the characteristics of the large-scale coronal magnetic structures in the regions where the activity leading to a cloud takes place. In this paper we use Hoeksema's potential field model of the solar magnetosphere to obtain the magnetic structure of the site of the solar events associated with 35 interplanetary magnetic clouds. The position of the related solar activity was determined from the location of the near-surface solar explosive events (flares and filament eruptions) associated with each cloud, obtained in our previous study. We find that the solar activity associated with interplanetary magnetic clouds occurs in regions of low-altitude, magnetically closed structures lying between higher helmets, or between the highest helmets and coronal holes, where the magnetic field lines are longitudinally oriented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005198620551
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  • 13
    Electronic Resource
    Electronic Resource
    Polar coronal holes and the sunspot cycle. A new method to predict sunspot numbers (1989)
    Springer
    Solar physics 122 (1989), S. 335-343 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Twenty years ago, Ohl (1966, 1968) found a correlation between geomagnetic activity around the minimum of the solar cycle and the Wolf sunspot number in the maximum of the following solar cycle. In this paper we shall show that such a relation means indeed a relation between the polar coronal holes area around the minimum of the solar cycle and the sunspot number in the maximum of the next. In fact, a very high positive correlation exists between the temporal evolution of the size of polar coronal holes and the Wolf sunspot number 6.3. years later.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00913000
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  • 14
    Electronic Resource
    Electronic Resource
    Solar flare activity and the structure of the coronal neutral line (1995)
    Springer
    Solar physics 160 (1995), S. 331-341 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this study we analyse the positions of major flares from 1978 and 1979, with respect to the magnetic structure of the solar corona, as described by a potential field model. We find that major flares exhibit no strong association with the neutral line at the chromospheric level. However, when we calculate the neutral line's position at higher and higher altitudes in the corona, we find that major flares show an increasing tendency to be found close to these high-altitude coronal neutral lines. The correlation between flares and higher-altitude coronal neutral lines reaches a maximum at an altitude of 0.35R ⊙, and thereafter decreases as the neutral line is moved out to the source surface at an altitude of 1.50R ⊙. This indicates that major flares are strongly associated with coronal structure at the 0.35R ⊙ level (≈ 250 000 km) - an altitude surprisingly high in the corona. This reinforces the idea that flares are associated with large-scale coronal magnetic fields and also indicates that the region of coronal magnetic topology important to solar flare processes may be larger than previously thought.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732811
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  • 15
    Electronic Resource
    Electronic Resource
    A solar scenario for the associated occurrence of flares, eruptive prominences, coronal mass ejections, coronal holes, and interplanetary shocks (1995)
    Springer
    Solar physics 161 (1995), S. 57-65 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The observation of non-corotating shock fronts in interplanetary space is always associated with the previous occurrence of a coronal mass ejection (CME), which is frequently accompanied by a flare or a prominence eruption. When looking at the solar region of origin of these events, a coronal hole is always found. Here we propose a scenario at the Sun where all these related events can find a place.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00732084
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  • 16
    Electronic Resource
    Electronic Resource
    Characteristics of coronal mass ejections associated with interplanetary shocks (1994)
    Springer
    Solar physics 151 (1994), S. 333-339 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a correlated study using coronagraph and interplanetary data from 1978 to 1983, a set of 56 coronal mass ejections (CMEs) was confidently associated with interplanetary shocks by Sheeleyet al. (1985). In this paper we analyze the characteristics of these particular CMEs in contrast to the whole population of them during the period. We find that the associated CMEs are not a representative sample of all the variety of CMEs and that they share specific characteristics. Contrary to common beliefs, these characteristics are not a high velocity or a large extension, but have more to do with the importance and shape of the CME. Practically all the CMEs associated with shocks were of importance Y (bright and/or large) and had a curved-type front structural class (a continuous curved front with either straight edges or curved legs). Another common characteristic of these particular CMEs is that they show a considerable increase in their angular span as they go out from the Sun, moving the peak of the distribution from ≃30° to ≃70°.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00679079
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  • 17
    Electronic Resource
    Electronic Resource
    The sources of large-scale heliospheric disturbances (1986)
    Springer
    Solar physics 106 (1986), S. 185-200 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Observations on a grid of 900 radio sources have been used to map and to track large-scale structures in the solar wind at distances of 0.6–1.5 AU from the Sun. Most of the disturbances were shells of enhanced density followed by high-speed streams lasting for several days, although more stable corotating interaction regions were also observed. Ninety-six disturbances were mapped during August 1978–September 1979 and those of the ‘erupting stream’-type were usually accompanied by shocks and geomagnetic activity if they encountered the Earth. Back-projection to the Sun indicated sources that were always associated with coronal holes. Possible associations with solar flares and disappearing filaments occurred but on many occasions no flare or filament activity was evident anywhere on the disc within a suitable time interval. It is concluded that erupting streams are transients generated by coronal hole activity. Evidence is presented which further suggests that coronal mass ejections of the ‘curved-front’ variety may be identified with these erupting streams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00161362
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  • 18
    Electronic Resource
    Electronic Resource
    Evolution of polar coronal holes and sunspots during cycles 21 and 22 (1994)
    Springer
    Solar physics 154 (1994), S. 377-384 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A very good correlation between the evolution of polar coronal hole size and sunspot number half a solar cycle later was found by Bravo and Otaola for solar cycle 21. In this paper we use a more complete set of data to reanalyse the relationship for solar cycle 21 and investigate the same relationship for solar cycle 22. We find that the complete set of data for cycle 21 yields a slightly different time shift for the best correlation between sunspots and holes and that the time shift for cycle 22 is different from that of cycle 21. However, because of limited availability of data of cycle 22, we consider it necessary to wait until the end of this cycle in order to decide if the difference is statistically significant or not. We also found that the time between successive peaks of smoothed polar hole area and smoothed sunspot number is the same in both cycles. This may provide a useful tool for the forecasting of future sunspot maxima. The constant of proportionality between polar coronal hole area and sunspot number can be seen to be different in both cycles. We discuss this difference and interpret it in terms of a different magnitude of the polar field strength in the two cycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00681106
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  • 19
    Electronic Resource
    Electronic Resource
    The Varying Multipolar Structure of the Sun's Magnetic Field and the Evolution of the Solar Magnetosphere Through the Solar Cycle (1998)
    Springer
    Solar physics 179 (1998), S. 223-235 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Sun's magnetic field extends far from the photosphere, into the corona, defining a magnetically dominated region before being drawn out radially by the solar wind flow. This region, where the internal sources of the solar field dominate the plasma structures and the energetic particle movement, can be properly considered the solar magnetosphere. The magnetic field in this region can be approximately described by models that extrapolate photospheric magnetic field observations under some simplifying assumptions. In this paper we use a potential field model which describes the solar field up to a source surface at 3.25 Rs, where the field is constrained to become radial. We present the variation of the magnitude and inclination of the various multipolar components throughout the solar magnetic cycle that characterise the changes in the structure of the solar magnetosphere over a period of 22 years. We also present some 3-D images of the coronal magnetic structure to show the global evolution of the solar magnetosphere throughout the solar cycle and discuss the importance of taking this structure into account in order to relate interplanetary and solar features.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005017329287
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  • 20
    Electronic Resource
    Electronic Resource
    THE CORRELATION BETWEEN SUNSPOT AND CORONAL HOLE CYCLES AND A FORECAST OF THE MAXIMUM OF SUNSPOT CYCLE 23 (1997)
    Springer
    Solar physics 173 (1997), S. 193-198 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have shown in previous papers that a close relationship exists between the evolution of polar coronal hole area, estimated from K-coronameter observations, and the Wolf sunspot number, with a time lag of about half a solar cycle. In this paper we study the same relationship, but with the total coronal hole area at the base of the corona as obtained from a potential field model of the coronal magnetic field, which provides a more complete series of about three solar cycles. We confirm the relationship for the two last cycles and find that the forward time shift in the coronal hole area for the best correlation with sunspot number is almost the same for cycles 21 and 22, and this shift is also the time between peaks in both series. We use this result to make an early prediction of the time and size of the sunspot maximum for solar cycle 23, and find that this should occur early in 2001 and have a magnitude of about 190, similar to that of the two previous sunspot cycles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004916427722
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