THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC MODELING OF PROPAGATING DISTURBANCES IN FAN-LIKE CORONAL LOOPS
THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC MODELING OF PROPAGATING DISTURBANCES IN FAN-LIKE CORONAL LOOPS
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DOI：
10.1088/2041-8205/775/1/l23
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发表时间：
2013-08
期刊：
影响因子：
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通讯作者：
Tongjiang Wang;L. Ofman;J. Davila
中科院分区：
文献类型：
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作者：
Tongjiang Wang;L. Ofman;J. Davila
准周期性传播强度扰动（PD）已被观察到在大日冕环的EUV图像超过十年，并被广泛接受为慢磁声波。然而，日出/EIS的光谱观测显示它们与持续的日冕上升流有关，这一解释值得商榷。出于这种情况下，日冕上升流可能是由零星的加热事件（nanoflares）在循环基地产生的众多个人流脉冲的累积结果，我们构建了一个速度驱动器与重复的微小脉冲，其能量频率分布遵循耀斑幂律缩放。然后，我们进行三维MHD建模的理想化的双极活动区，通过应用这种宽带速度驱动器的大冠状循环出现在计算域中打开的足点。我们的模型成功地再现了PD与观察到的类似功能，并表明，任何上升流脉冲不可避免地激发慢磁声波扰动传播沿着环路。我们发现，所产生的PD的波签名占主导地位，因为它们的传播速度是一致的，在流动的存在下的波的速度，和注入的流量迅速减速与高度。我们的模拟结果表明，所观察到的PD和相关的持续上升流可能是由小规模的脉冲加热事件（nanoflares）在环基地在日冕，和流动和波可能都有助于PD在较低的高度。
Quasi-periodic propagating intensity disturbances (PDs) have been observed in large coronal loops in EUV images over a decade, and are widely accepted to be slow magnetosonic waves. However, spectroscopic observations from Hinode/EIS revealed their association with persistent coronal upflows, making this interpretation debatable. Motivated by the scenario that the coronal upflows could be the cumulative result of numerous individual flow pulses generated by sporadic heating events (nanoflares) at the loop base, we construct a velocity driver with repetitive tiny pulses, whose energy frequency distribution follows the flare power-law scaling. We then perform three-dimensional MHD modeling of an idealized bipolar active region by applying this broadband velocity driver at the footpoints of large coronal loops which appear open in the computational domain. Our model successfully reproduces the PDs with similar features as the observed, and shows that any upflow pulses inevitably excite slow magnetosonic wave disturbances propagating along the loop. We find that the generated PDs are dominated by the wave signature as their propagation speeds are consistent with the wave speed in the presence of flows, and the injected flows rapidly decelerate with height. Our simulation results suggest that the observed PDs and associated persistent upflows may be produced by small-scale impulsive heating events (nanoflares) at the loop base in the corona, and that the flows and waves may both contribute to the PDs at lower heights.