HIGH-RESOLUTION CALCULATIONS OF THE SOLAR GLOBAL CONVECTION WITH THE REDUCED SPEED OF SOUND TECHNIQUE. I. THE STRUCTURE OF THE CONVECTION AND THE MAGNETIC FIELD WITHOUT THE ROTATION
HIGH-RESOLUTION CALCULATIONS OF THE SOLAR GLOBAL CONVECTION WITH THE REDUCED SPEED OF SOUND TECHNIQUE. I. THE STRUCTURE OF THE CONVECTION AND THE MAGNETIC FIELD WITHOUT THE ROTATION
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DOI：
10.1088/0004-637x/786/1/24
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
H. Hotta;M. Rempel;T. Yokoyama
中科院分区：
文献类型：
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作者：
H. Hotta;M. Rempel;T. Yokoyama
我们对太阳全球对流进行了非旋转的高分辨率计算，该计算解决了小于10 Mm的对流尺度。为了应对低对流区的低马赫数条件，我们使用了简化的声速技术（RSST），该技术实现简单，在并行计算中只需要本地通信。此外，RSST允许我们将计算范围向上扩展到约0.99 R☉，因为它也可以处理可压缩流。利用这种方法，我们在全球尺度上研究了太阳对流区，包括小尺度近地表对流。特别地，我们研究了顶边界条件对整个对流区对流结构以及小尺度发电机作用的影响。我们的主要结论如下。(1)在近地表产生的小尺度下流在一定程度上渗透到更深层，并激发>0.9 R☉区域的小尺度湍流，其中R☉是太阳半径。(2)在较深的对流区（<0.9 R☉），对流不受上界位置的影响。(3)采用大涡模拟方法，可以实现小规模的发电机作用，在整个对流区保持约0.15Beq-0.25Beq的磁场，其中Beq为磁场与动能的均分。(4)对流区总体发电机效率受坡印亭通量向下和固有对流尺度深度变化的影响。
We carry out non-rotating high-resolution calculations of the solar global convection, which resolve convective scales of less than 10 Mm. To cope with the low Mach number conditions in the lower convection zone, we use the reduced speed of sound technique (RSST), which is simple to implement and requires only local communication in the parallel computation. In addition, the RSST allows us to expand the computational domain upward to about 0.99 R☉, as it can also handle compressible flows. Using this approach, we study the solar convection zone on the global scale, including small-scale near-surface convection. In particular, we investigate the influence of the top boundary condition on the convective structure throughout the convection zone as well as on small-scale dynamo action. Our main conclusions are as follows. (1) The small-scale downflows generated in the near-surface layer penetrate into deeper layers to some extent and excite small-scale turbulence in the region >0.9 R☉, where R☉ is the solar radius. (2) In the deeper convection zone (<0.9 R☉), the convection is not influenced by the location of the upper boundary. (3) Using a large eddy simulation approach, we can achieve small-scale dynamo action and maintain a field of about 0.15Beq–0.25Beq throughout the convection zone, where Beq is the equipartition magnetic field to the kinetic energy. (4) The overall dynamo efficiency varies significantly in the convection zone as a consequence of the downward directed Poynting flux and the depth variation of the intrinsic convective scales.