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arXiv 1603.07129astro-ph.SR
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日冕加热的观测驱动动力学方法

An observationally-driven kinetic approach to coronal heating

K. Moraitis, A. Toutountzi, H. Isliker, M. Georgoulis, L. Vlahos, G. Chintzoglou

摘要:

日冕加热通过磁能量的爆炸释放仍然是太阳物理学中的一个悬而未决的问题。最近的流体动力学模型试图通过在模拟的一维日冕环中随机地点和时间放置成群的“纳米耀斑”来进行调查。我们利用观测到的太阳活动区的外推日冕磁场,在三维空间中研究了这个问题。本文利用NOAA活动区AR 11158观测到的光球磁图进行了非线性无力场外推。然后,我们确定的位置,能量含量和体积的“不稳定”的地区,即地区容易释放磁能,由于当地积累的电流密度。这些体积和它们的分形维数的统计分布推断,调查也依赖于空间分辨率。进一步采用一个简单的电阻率模型,我们推断的分形分布的电场在这些体积的属性。接下来,我们通过跟踪10 ^5粒子(电子和离子)在所产生的电场中的轨迹和运动轨迹,监测它们在10 eV温度下服从初始麦克斯韦分布的演化。为了计算方便,磁场外推的长度元素是1弧秒,比低日冕中的粒子碰撞平均自由程粗得多。碰撞的存在将大部分等离子体捕获在不稳定体积或电流片(UCS)周围,只有分布的尾部获得大量能量。假设UCS之间的距离类似于碰撞平均自由程,我们发现低活性区电晕被加热到100-200 eV,对应于超过2 MK的温度,电子在几十秒内,离子在几千秒内。分形分布的,纳米片触发的碎片状UCS...

英文摘要:

Coronal heating through the explosive release of magnetic energy remains an open problem in solar physics. Recent hydrodynamical models attempt an investigation by placing swarms of 'nanoflares' at random sites and times in modeled one-dimensional coronal loops. We investigate the problem in three dimensions, using extrapolated coronal magnetic fields of observed solar active regions. We apply a nonlinear force-free field extrapolation above an observed photospheric magnetogram of NOAA active region (AR) 11158. We then determine the locations, energy contents, and volumes of 'unstable' areas, namely areas prone to releasing magnetic energy due to locally accumulated electric current density. Statistical distributions of these volumes and their fractal dimension are inferred, investigating also their dependence on spatial resolution. Further adopting a simple resistivity model, we infer the properties of the fractally distributed electric fields in these volumes. Next, we monitor the evolution of 10^5 particles (electrons and ions) obeying an initial Maxwellian distribution with a temperature of 10 eV, by following their trajectories and energization when subjected to the resulting electric fields. For computational convenience, the length element of the magnetic-field extrapolation is 1 arcsec, much coarser than the particles collisional mean free path in the low corona. The presence of collisions traps the bulk of the plasma around the unstable volumes, or current sheets (UCS), with only a tail of the distribution gaining substantial energy. Assuming that the distance between UCS is similar to the collisional mean free path we find that the low active-region corona is heated to 100-200 eV, corresponding to temperatures exceeding 2 MK, within tens of seconds for electrons and thousands of seconds for ions. Fractally distributed, nanoflare-triggening fragmented UCS ...

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