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arXiv 1402.3474astro-ph.SR
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作为磁场II的函数的连续强度。局部磁通量和对流

The continuum intensity as a function of magnetic field II. Local magnetic flux and convective flows

P. Kobel, S. K. Solanki, J. M. Borrero

摘要:

为了加深我们对太阳活动区(AR)和宁静太阳(QS)小尺度磁场对太阳辐照度的作用的理解,研究其连续亮度的物理过程是至关重要的。先前的结果表明,在QS中的磁性元素达到更大的连续强度比AR在磁盘中心,但离开这种差异无法解释。利用Hinode/SP盘心资料,研究了局部磁通量对对流强度和连续强度对比度的影响。通过Milne-Eddington反演(VFISV代码)检索了表观(即在一个像素上平均)纵向场强和视线(LOS)等离子体速度。我们分析了一系列在AR谱段和QS上采集的盒子,以确定磁性元素的连续强度对比度、垂直流的振幅和盒子平均对比度如何受到盒子中平均纵向场强的影响(盒子中的总无符号通量与之成比例)。我们的研究结果表明,作为磁通量增加局部(例如,从弱网络到强plage),加热的磁性元件减少了中间的更大和更强的磁补丁内的对流能量传输的抑制。这一点,再加上已知存在的较大的磁性特征,可以解释先前发现的AR中最亮磁性元素的对比度低于QS。对流的抑制也影响光球区域的平均连续亮度,因此在圆盘中心,一个强网络或斑的光球区域比一个纯粹安静的区域显得更暗。这与三维MHD模拟的预测定性一致。

英文摘要:

To deepen our understanding of the role of small-scale magnetic fields in active regions (ARs) and in the quiet Sun (QS) on the solar irradiance, it is fundamental to investigate the physical processes underlying their continuum brightness. Previous results showed that magnetic elements in the QS reach larger continuum intensities than in ARs at disk center, but left this difference unexplained. We use Hinode/SP disk center data to study the influence of the local amount of magnetic flux on the vigour of the convective flows and the continuum intensity contrasts. The apparent (i.e. averaged over a pixel) longitudinal field strength and line-of-sight (LOS) plasma velocity were retrieved by means of Milne-Eddington inversions (VFISV code). We analyzed a series of boxes taken over AR plages and the QS, to determine how the continuum intensity contrast of magnetic elements, the amplitude of the vertical flows and the box-averaged contrast were affected by the mean longitudinal field strength in the box (which scales with the total unsigned flux in the box). Our results suggest that as the magnetic flux increases locally (e.g. from weak network to strong plage), the heating of the magnetic elements is reduced by the intermediate of a more suppressed convective energy transport within the larger and stronger magnetic patches. This, together with the known presence of larger magnetic features, could explain the previously found lower contrasts of the brightest magnetic elements in ARs compared to the QS. The inhibition of convection also affects the average continuum brightness of a photospheric region, so that at disk center, an area of photosphere in strong network or plage appears darker than a purely quiet one. This is qualitatively consistent with the predictions of 3D MHD simulations.

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