First Unambiguous Imaging of Large-scale Quasi-periodic Extreme-ultraviolet Wave or Shock

Abstract

We report the first unambiguous quasi-periodic large-scale extreme-ultraviolet (EUV) wave or shock that was detected by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. During the whip-like unwinding eruption of a small filament on 2012 April 24, multiple consecutive large-scale wavefronts emanating from AR11467 were observed simultaneously along the solar surface and a closed transequatorial loop system. In the meantime, an upward propagating dome-shaped wavefront was also observed, whose initial speed and deceleration are about 1392 km s −1 and 1.78 km s −2 , respectively. Along the solar surface, the quasi-peridoic wavefronts had a period of about 163±21 seconds and propagated at a nearly constant speed of 747±26 km s −1 ; they interacted with active region AR11469 and launched a sympathetic upward propagating secondary EUV wave. The wavefronts along the loop system propagated at a speed of 897 km s −1 , and they were reflected back at the southern end of the loop system at a similar speed. In addition to the propagating waves, a standing kink wave was also present in the loop system simultaneously. Periodicity analysis reveals that the period of the wavefronts was consistent with that of the unwinding helical structures of the erupting filament. Based on these observational facts, we propose that the observed quasi-periodic EUV wavefronts were most likely excited by the periodic unwinding motion of the filament helical structures. In addition, two different seismological methods are applied to derive the magnetic field strength of the loop system, and for the first time the reliability of these inversion techniques are tested with the same magnetic structure.

Research progress on coronal extreme ultraviolet waves

“…EUV波具有穹顶状形态, CME被包围在其 内部. 研究发现, 圆顶状EUV波径向部分的速度是侧向 部分的1.3~2.3倍 [45,47,48] ; 射电观测也揭示了类似的关 系 [48] . EUV波不同部分传播速度的差异可能是由CME…”

“…另外, 与EUV波相关的大尺度扰动信号也可在射 电米波和微波观测图像上探测到 [62~65] . Shen和Liu [ , 并且采用射电II型暴推算的波速与成像观测测量 得到的波速一致 [34,45] . 但是, 如果考虑所有EUV波, 它与 射电II型暴之间的相关性却不高 [28,69~71] .…”

“…如果是前者, 那么次级日冕暗化现象便更支持 [110,111] . 后来又发现, 在没有莫尔顿波的情况 下, EUV波也会导致暗条发生横向振荡 [44,45,90,112,113] . 当 日面上有多个暗条时, 因EUV波到达不同暗条需要的时 间不同, 暗条将按离爆发源区距离远近依次发生振荡运 动 [20,112] .…”

“…当EUV波作用于暗条的角度不同时将触发不 同模式的暗条振荡: EUV波垂直(平行)作用于暗条轴向 时将激发横向(纵向)暗条振荡 [114] ; 二者呈锐角相互作用 时将导致暗条同时发生纵向和横向振荡 [115] . EUV波通 常还会引起冕环和盔状流发生横向振荡 [44,45,51,59] . 在21世纪初人们便认识到大尺度波动可以触发太 阳活动的连续发生.…”

“…QFP波时常在传播过程中表现出明显的波动效 应. 比如, 与强磁场结构作用发生明显的折射效应进而 改变传播方向 [23,94] ; 沿闭合磁力线传播时, 波前在磁力 线另一端被反射并导致闭合磁环的振荡等 [19,45,133] .…”