Little attention has been paid to group velocities of three-dimensional (3D) MHD waves in solar coronal seismology. This study aims to present a rather comprehensive examination on the group velocities of trapped 3D kink modes in coronal slabs, emphasizing the connection of mode analysis to both mode characterization and impulsively excited 3D kink waves. We work in linear, ideal, pressureless MHD, and take the equilibrium slab to be symmetrically structured only in one transverse direction. The dispersion relation is numerically solved, with the results understood by making in-depth analytical progress. We address both the transverse fundamental and its first overtone. We develop a three-subgroup scheme for categorizing 3D kink modes on the plane spanned by the axial and out-of-plane wavenumbers. The group ($\vec{v}_{\rm gr}$) and phase velocities ($\vec{v}_{\rm ph}$) sit on the same side of the equilibrium magnetic field ($\vec{B}_0$) for the ``$\vec{B}_0$-same-side A'' and ``$\vec{B}_0$-same-side F'' subgroups, which are further discriminated by the directional similarity of $\vec{v}_{\rm gr}$ and $\vec{B}_0$. The ``$\vec{B}_0$-straddling'' subgroup is peculiar in that $\vec{v}_{\rm gr}$ and $\vec{v}_{\rm ph}$ lie astride $\vec{B}_0$, a feature that cannot be found for waves in unbounded uniform media in pressureless MHD. This ``$\vec{B}_0$-straddling'' subgroup pertains to both the fundamental and its overtones. We further place our results in the context of impulsive waves, employing the method of stationary phase to predict the large-time wavefront morphology in the plane of symmetry of the equilibrium slab. Wavefronts directed toward $\vec{B}_0$ derive exclusively from ``$\vec{B}_0$-straddling'' modes, and are confined to narrow sectors.
Magnetic swirls and associated fast magnetoacoustic kink waves in a solar chromospheric flux tube
我们进行了数值模拟脉冲产生的磁漩涡在一个孤立的通量管，这是植根于太阳光球。这些漩涡是由速度的水平分量中的初始脉冲触发的。初始脉冲或者：（a）在局部磁通量管内的中心发射;或者（b）在周围介质中偏离中心发射。磁通管的演变和动力学是由三维的，理想的磁流体动力学方程。通过数值求解这些方程，发现在（a）情况下，产生了与快磁声扭折和$m=1$ Alfvén波相关的偶极状涡旋。在情况（b）中，快磁声扭折和$m=0$ Alfvén模式被激发。在这两种情况下，激发的快磁声扭折波和阿尔文波由相似的流型组成，磁壳也由顺时针和逆时针旋转的等离子体产生，这可以是偶极形色球漩涡的代理。涡旋和波扰动的复杂动力学揭示了足够数量的能量的通道，以满足色球层（$\sim$ 10 $^{4}$ W m $^{-1}$）和日冕（$\sim$ 10 $^{2}$ W m $^{-1}$）中的能量损失。其中一些数字发现让人想起最近观测数据中的特征。
Key Laboratory of Solar Activity and Space Weather, School of Aerospace, Harbin Institute of Technology, Shenzhen（哈尔滨工业大学深圳航天学院太阳活动与空间天气重点实验室）；Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick（华威大学物理部聚变、太空与天体物理中心）；G-LAMP NEXUS Institute/School of Space Research, Kyung Hee University（庆熙大学太空研究学院 G-LAMP NEXUS 研究所）；Centro de Investigacion en Astronomía, Universidad Bernardo O’Higgins（贝尔纳多·奥希金斯大学天文学研究中心）；Institute of Solar-Terrestrial Physics SB RAS（俄罗斯科学院西伯利亚分院太阳-地球物理研究所）
