Magnetic evolution of superactive regions - Complexity and potentially unstable magnetic discontinuities
Magnetic evolution of superactive regions - Complexity and potentially unstable magnetic discontinuities
复制标题
超活跃区域的磁演化 - 复杂性和潜在不稳定的磁不连续性
DOI：
10.1051/0004-6361/200912044
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发表时间：
2009
影响因子：
6.5
通讯作者：
F. Giorgi
中科院分区：
文献类型：
--
作者：
S. Criscuoli;P. Romano;F. Zuccarello;F. Giorgi
上下文人们普遍认为，太阳耀斑是太阳大气中发生的磁重联事件的表现。这些事件的几个方面仍然不清楚，虽然许多努力已经致力于调查耀斑发生地点的磁场配置。目标。在这项工作中，我们已经研究了超活动区域的样本的一些属性的时间演化，目的是挑选出最重要的耀斑活动预测。方法.我们研究了2000年1月1日至2006年12月31日期间用MDI/SOHO仪器观测到的14个超活动区的性质，这些超活动区的特征是在它们通过太阳盘期间特别强烈的耀斑活动。我们分析了光球磁场的分形和多重分形性质的时间演化，即广义分形维数和贡献和维的diligence，它描述了磁场的几何性质，以及潜在的不稳定体积的磁不连续性以上的研究AR，这可能提供信息的磁场配置在大气上层。还估计了这些量与耀斑指数的相关性，耀斑指数提供了关于一个区域的耀斑活动的信息。结果我们发现，在我们的样本的50%的广义分形维数与耀斑指数计算超过50小时的窗口，而贡献的多样性和维度多样性的相关性与相同的指数。一个明显的增加的潜在的不稳定体积的磁不连续的日冕观察之前的阶段，其特征在于更频繁和更强烈的耀斑。我们还发现，自由能分布函数的不稳定体积的分析超活性区可以拟合直线的斜率大于在以前的作品中发现的值为不太活跃的磁性区域。结论.广义分形维数和磁不连续的潜在不稳定体积是最适合的统计调查与耀斑活动的关系在较长的时间间隔（50小时）和较短的时间间隔（几个小时），分别。
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.