标题： 磁流体动力学波在太阳日冕弧中的三维传播 显示英文标题

标题： Three-Dimensional Propagation of Magnetohydrodynamic Waves in Solar Coronal Arcades

摘要： 我们通过包含扰动的三维传播，数值研究了二维日冕弧中振荡的激发和时间演化。 通过在零β近似下求解线性理想磁流体动力学（MHD）方程，研究了瞬时生成的扰动的时间演化。 由于我们忽略了气体压力，慢模式不存在，因此只剩下耦合的MHD快模式和阿尔芬模式。 进行了两种类型的数值实验。 首先，分析了系统中的一个快模与局部阿尔芬波之间的共振波能传递。 可以看到，由于共振耦合，具有全局特征的快波将其能量转移到日冕弧中某一特定磁面上的局域阿尔芬振荡，从而导致初始快MHD模式的阻尼。 其次，考虑了局部瞬时激励的时间演化，试图模拟附近的日冕扰动。 在这种情况下，生成的快波前在其能量上留给了日冕弧内的多个磁面。 因此，即使没有密度增强（如日冕环中的情况），系统仍能以阿尔芬振荡的形式捕获能量。 这些局部振荡随后被相位混合到更小的空间尺度。 系统通过波能转换捕获的波能数量强烈依赖于垂直方向扰动的波长，但几乎与磁场尺度高度与密度尺度高度的比值无关。 显示英文摘要

摘要： We numerically investigate the excitation and temporal evolution of oscillations in a two-dimensional coronal arcade by including the three-dimensional propagation of perturbations. The time evolution of impulsively generated perturbations is studied by solving the linear, ideal magnetohydrodynamic (MHD) equations in the zero-beta approximation. As we neglect gas pressure the slow mode is absent and therefore only coupled MHD fast and Alfv\'en modes remain. Two types of numerical experiments are performed. First, the resonant wave energy transfer between a fast normal mode of the system and local Alfv\'en waves is analyzed. It is seen how, because of resonant coupling, the fast wave with global character transfers its energy to Alfv\'enic oscillations localized around a particular magnetic surface within the arcade, thus producing the damping of the initial fast MHD mode. Second, the time evolution of a localized impulsive excitation, trying to mimic a nearby coronal disturbance, is considered. In this case, the generated fast wavefront leaves its energy on several magnetic surfaces within the arcade. The system is therefore able to trap energy in the form of Alfv\'enic oscillations, even in the absence of a density enhancement such as that of a coronal loop. These local oscillations are subsequently phase-mixed to smaller spatial scales. The amount of wave energy trapped by the system via wave energy conversion strongly depends on the wavelength of perturbations in the perpendicular direction, but is almost independent from the ratio of the magnetic to density scale heights.