On the reliability of the fractal dimension measure of solar magnetic features and on its variation with solar activity

Criscuoli, S.; Rast, Mark; Ermolli, I.; Centrone, Mauro

doi:10.1051/0004-6361:20065951

Cited by 22 publications

(17 citation statements)

References 21 publications

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“…This scale invariance is consistent with the proposal that the magnetic field forms a fractal (or multifractal) pattern at the solar surface (e.g., Roudier and Muller 1987;Lawrence et al 1995;Komm 1995;Nesme-Ribes et al 1996;Meunier 1999Meunier , 2004Holzreuter 2002, 2003;Abramenko 2005;Criscuoli et al 2007). Since magnetic features are moved around by the evolving convection cells, possibly such an analysis provides more information on the distribution of convection at different scales, rather than on intrinsic magnetic properties.…”

Section: Quiet Sun Magnetic Fieldssupporting

confidence: 87%

Small-Scale Solar Magnetic Fields

et al. 2008

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As we resolve ever smaller structures in the solar atmosphere, it has become clear that magnetism is an important component of those small structures. Small-scale magnetism holds the key to many poorly understood facets of solar magnetism on all scales, such as the existence of a local dynamo, chromospheric heating, and flux emergence, to name a few. Here, we review our knowledge of small-scale photospheric fields, with particular emphasis on quiet-sun field, and discuss the implications of several results obtained recently using new instruments, as well as future prospects in this field of research.

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Section: Quiet Sun Magnetic Fieldssupporting

confidence: 87%

Small-Scale Solar Magnetic Fields

et al. 2008

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“…16. This result agrees with previous results (Janßen et al 2003;Criscuoli et al 2007). In our work, the relative continuum intensity distribution at the locations of magnetic elements reaches a peak at 0.97, which shows that many magnetic elements located in the areas where the relative continuum intensity are lower than the average continuum intensity.…”

Section: Conclusion and Discussionsupporting

confidence: 94%

Properties of magnetic elements in the quiet Sun using the marker-controlled watershed method

Xie

Zhang

et al. 2009

A&A

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Context. The quiet Sun is an important part of understanding the global magnetic properties of the Sun. A recently launched observation system, named HINODE, provides a lot of high-resolution images for studying the quiet Sun. Obviously, it is time-consuming to analyze these images by hand. It is desirable to develop a technique for recognizing magnetic elements, thus automatically computing magnetic properties and the relationship between magnetic elements and granulation. Aims. We design an automatic method of recognizing magnetic elements based on the features of HINODE magnetograms and of measuring their properties. Then we study the relationship between magnetic elements and granulation. Methods. We used the magnetogram, continuum image, and Dopplergram on April 16, 2007, which were taken with the Solar Optical Telescope instrument aboard HINODE. The field of view is 147. 60 × 162. 30 in a quiet solar region, locating at disk center. We introduced the mark-controlled watershed method to detect magnetic elements automatically, because it is a popular image-segmentation method for dealing with overlapping objects. We took the centers that are the local maximum in all directions as the marks for restraining over-segmentation. We computed the properties of the detected magnetic elements and the relation among magnetic field strength, relative continuum intensity, and Doppler velocity at the same locations of magnetic elements. Results. We obtain the following results: (1) 34% of our observation region are covered by magnetic fields; (2) the magnetic flux distribution of all elements reaches a peak at 1.07 × 10 16 Mx for the whole region; (3) the relative continuum intensity distribution at the locations of magnetic elements reaches a peak at 0.97, which shows that the majority of magnetic elements located at the areas where the relative continuum intensity is less than its average. The relative continuum intensities in the areas with strong flux density are the median, meaning that the strong magnetic elements are usually located at the boundary of granulation; (4) the absolute Doppler velocity distribution at the locations of magnetic elements reaches a peak at 1.00 km s −1 , and the majority of weak magnetic elements located at the areas where the absolute velocity is greater than 1.00 km s −1 ; (5) strongly magnetized regions only have weak absolute Doppler velocities. The absolute velocity is lower than 1.00 km s −1 in the regions where the magnetic flux density of elements is higher than 100 G.

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“…A similar investigation was carried out by Georgoulis (2005), who also presented the multifractal analyses as more suitable than the fractal one for flare forecasting. Statistical analysis of large samples of data have shown that variations of fractal properties of ARs in photosphere (Meunier 2004) and low chromosphere (Criscuoli et al 2007) do not present clear trends with the activity cycle. On the contrary, McAteer et al (2005) reported a correlation between variations of photospheric fractal properties of ARs with flare productivity.…”

Section: Introductionmentioning

confidence: 99%

Magnetic evolution of superactive regions

Criscuoli¹,

Romano²,

Zuccarello³

et al. 2009

A&A

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Context. It is widely accepted that solar flares are manifestations of magnetic reconnection events taking place in the solar atmosphere. Several aspects of these events remain unclear, although many efforts have been devoted to the investigation of magnetic field configurations at flare occurrence sites. Aims. In this work, we have studied the temporal evolution of some properties of a sample of superactive regions with the aim to single out the most significant for flare activity forecasting. Methods. We have investigated properties of 14 superactive regions, observed between January 1st 2000 and December 31st 2006 with MDI/SOHO instrument and characterized by a particularly intense flare activity during their passage on the solar disk. We have analyzed the temporal evolution of fractal and multifractal properties of photospheric magnetic fields, namely the generalized fractal dimension and the contribution and dimensional diversities, which describe geometrical properties of the magnetic field, as well as the potential unstable volumes of magnetic discontinuities above the studied ARs, which may provide information about the magnetic field configuration in upper layers of the atmosphere. Correlations of these quantities with the flare index, which provides information about the flare activity of a region, have also been estimated. Results. We found that in 50% of our sample the generalized fractal dimension is correlated with the flare index computed over windows of 50 h, while the contribution diversity and the dimensional diversity are anticorrelated with the same index. A clear increase of the potential unstable volume of magnetic discontinuities in the corona is observed before the phases characterized by more frequent and intense flares. We also found that the free energy distribution functions of unstable volumes of the analyzed superactive regions can be fitted with straight lines whose slope is larger than the values found in previous works for less active magnetic regions. Conclusions. The generalized fractal dimension and the potential unstable volume of magnetic discontinuities are the most suitable for statistical investigations of relations with flare activity over longer (50 h) and shorter (few hours) time intervals, respectively.

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On the reliability of the fractal dimension measure of solar magnetic features and on its variation with solar activity

Cited by 22 publications

References 21 publications

Small-Scale Solar Magnetic Fields

Small-Scale Solar Magnetic Fields

Properties of magnetic elements in the quiet Sun using the marker-controlled watershed method

Magnetic evolution of superactive regions

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