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Solar Surface Convection

机译:太阳表面对流

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We review the properties of solar convection that are directly observable at the solar surface, and discuss the relevant underlying physics, concentrating mostly on a range of depths from the temperature minimum down to about 20 Mm below the visible solar surface. The properties of convection at the main energy carrying (granular) scales are tightly constrained by observations, in particular by the detailed shapes of photospheric spectral lines and the topology (time- and length-scales, flow velocities, etc.) of the up- and downflows. Current supercomputer models match these constraints very closely, which lends credence to the models, and allows robust conclusions to be drawn from analysis of the model properties. At larger scales the properties of the convective velocity field at the solar surface are strongly influenced by constraints from mass conservation, with amplitudes of larger scale horizontal motions decreasing roughly in inverse proportion to the scale of the motion. To a large extent, the apparent presence of distinct (meso- and supergranulation) scales is a result of the folding of this spectrum with the effective "filters" corresponding to various observational techniques. Convective motions on successively larger scales advect patterns created by convection on smaller scales; this includes patterns of magnetic field, which thus have an approximately self-similar structure at scales larger than granulation. Radiative-hydrodynamical simulations of solar surface convection can be used as 2D/3D time-dependent models of the solar atmosphere to predict the emergent spectrum. In general, the resulting detailed spectral line profiles agree spectacularly well with observations without invoking any micro- and macroturbulence parameters due to the presence of convective velocities and atmosphere inhomogeneities. One of the most noteworthy results has been a significant reduction in recent years in the derived solar C, N, and O abundances with far-reaching consequences, not the least for helioseismology. Convection in the solar surface layers is also of great importance for helioseismology in other ways; excitation of the wave spectrum occurs primarily in these layers, and convection influences the size of global wave cavity and, hence, the mode frequencies. On local scales convection modulates wave propagation, and supercomputer convection simulations may thus be used to test and calibrate local helioseismic methods. We also discuss the importance of near solar surface convection for the structure and evolution of magnetic patterns: faculae, pores, and sunspots, and briefly address the question of the importance or not of local dynamo action near the solar surface. Finally, we discuss the importance of near solar surface convection as a driver for chromospheric and coronal heating.
机译:我们回顾了可直接在太阳表面观测到的太阳对流特性,并讨论了相关的基础物理学,主要集中在从最低温度到可见太阳表面以下约20 Mm的深度范围。对流在主要能量携带(颗粒)尺度上的性质受到观测的严格限制,特别是受到光球光谱线的详细形状和上升波的拓扑结构(时间尺度和长度尺度,流速等)的严格限制。和下流。当前的超级计算机模型非常紧密地匹配这些约束,这使模型具有可信度,并允许通过对模型属性的分析得出可靠的结论。在较大的尺度上,太阳表面对流速度场的性质受到质量守恒因素的强烈影响,较大尺度的水平运动的幅度与运动尺度成反比地减小。在很大程度上,不同尺度(中粒和超粒化)的表观存在是由于该频谱被对应于各种观测技术的有效“过滤器”折叠的结果。连续较大尺度上的对流运动将平移由较小尺度上的对流产生的模式;这包括磁场模式,因此具有比颗粒更大的自相似结构。太阳表面对流的辐射流体动力学模拟可以用作太阳大气的2D / 3D时间相关模型来预测出现的光谱。通常,由于对流速度和大气不均匀性的存在,所得的详细光谱线轮廓与观测结果非常吻合,而无需调用任何微湍流和大湍流参数。最值得注意的结果之一是,近年来,太阳C,N和O的丰度大大降低,产生了深远的影响,尤其是对于日震学。太阳表面层中的对流在其他方面对日震学也很重要。频谱的激发主要发生在这些层中,对流会影响整体波腔的大小,进而影响模式频率。在局部尺度上,对流可调制波的传播,因此超级计算机对流模拟可用于测试和校准局部偏震方法。我们还讨论了近太阳表面对流对磁模式的结构和演化的重要性:云状,孔隙和黑子,并简要讨论了太阳表面附近局部发电机作用的重要与否的问题。最后,我们讨论了近太阳表面对流作为色球和日冕加热的驱动因素的重要性。

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