太阳物理研究组知识库

磁重联在宇宙的许多动力学现象中都是非常核心的过程.磁流体动力学（MHD）数值模拟是研究磁重联过程以及相应物理图像的一种很有效的手段.通过不同的参数组合,来研究MHD数值模拟中磁雷诺数和空间分辨率对磁重联率、数值耗散和能谱分布的影响.对得到的数据进行分析后,发现磁雷诺数对磁重联率和能谱分布有一定的影响.磁雷诺数越大,磁重联过程进入非线性阶段所需的特征时间越短,磁重联率就越早发生跃升.磁雷诺数R_m对耗散开始发挥作用的Kolmogorov微观尺度l_ko有明显影响:R_m越大,l_ko就越小.研究了磁重联过程中包括数值耗散在内的额外耗散对重联过程的影响.结果表明,撕裂模不稳定性开始之前的额外耗散以纯数值耗散为主,撕裂模不稳定性出现之后,额外耗散出现同步跃升,说明不稳定性导致的湍流明显增强了耗散的效果,相当于在局部湍流区引入了超电阻.能谱分析进一步表明,大尺度电流片的l_ko完全可能出现在宏观的MHD尺度上. 

Magnetic reconnection (MR) is one of the most important physical process for many dynamical phenomena in the universe.  Magnetohydrodynamical (MHD) simulation is an effective way to study the potential mechanisms related to the MR. In this paper, we investigate the influence of Magnetic Reynolds number and numerical resolution on the reconnection rate, numerical diffusion and energy spectrum. We have found that magnetic Reynolds number has some impact on the reconnection rate and energy spectrum distribution. The characteristic time for engaging into the non-linear phase will be earlier as the Reynold number increases. When it comes to the tearing phase, reconnection rate will increase rapidly. On the other hand, magnetic Reynolds number Rm affects significantly the Kolmogorov microscopic scale lko, which becomes smaller as Rm increases. Additional dissipation is defined as combined effect between numerical diffusion and turbulent dissipation. We find that the additional dissipation is dominated by numerical diffusion before the tearing mode instability takes place. After the instability develops, the additional dissipation rises vastly, which indicates that turbulence can enhance the diffusion. Through the spectrum study, the energy dissipation might take place at the macroscopic MHD scale.