Solar supergranulation revealed by granule tracking
Solar supergranulation revealed by granule tracking
复制标题
通过粒子追踪揭示太阳超粒化现象
DOI：
10.1051/0004-6361:20079077
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发表时间：
2008
影响因子：
6.5
通讯作者：
L. Parès
中科院分区：
文献类型：
--
作者：
M. Rieutord;N. Meunier;T. Roudier;S. Rondi;F. Beigbeder;L. Parès
上下文超微粒化是太阳表面速度场的一种模式，人们已经知道了50多年，然而，对于它的起源还没有令人满意的解释。目标。因此，需要新的观测约束来指导理论方法，这些方法在引起表面湍流对流的大规模不稳定性或浮力的直接强迫的情景之间犹豫不决。方法.使用Pic-du-Midi天文台的14 Mpixel CALAS相机，我们获得了7.5 h长的高分辨率图像序列，具有前所未有的视场大小。跟踪颗粒，我们已经确定了在太阳表面的速度场非常详细的规模为2.5毫米至250毫米。结果。动能密度谱显示，超颗粒化的峰值在36微米，尺度范围在20微米到75微米之间。在小尺度下，超颗粒流的减少接近于k −2幂律，比均分柯尔莫哥洛夫定律更陡。发散场的概率分布函数显示了超颗粒的不稳定性的特征，因此也显示了它的湍流性质。
Context. Supergranulation is a pattern of the velocity field at the surface of the Sun, which has been known about for more than fifty years, however, no satisfactory explanation of its origin has been proposed. Aims. New observational constraints are therefore needed to guide theoretical approaches which hesitate between scenarios that either invoke a large-scale instability of the surface turbulent convection or a direct forcing by buoyancy. Methods. Using the 14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained a 7.5 h-long sequence of high resolution images with unprecedented field size. Tracking granules, we have determined the velocity field at the Sun’s surface in great detail from a scale of 2.5 Mm up to 250 Mm. Results. The kinetic energy density spectrum shows that supergranulation peaks at 36 Mm and spans on scales ranging between 20 Mm and 75 Mm. The decrease of supergranular flows in the small scales is close to a k −2 -power law, steeper than the equipartition Kolmogorov one. The probability distribution function of the divergence field shows the signature of intermittency of the supergranulation and thus its turbulent nature.