In Situ Generation of Transverse Magnetohydrodynamic Waves from Colliding Flows in the Solar Corona
In Situ Generation of Transverse Magnetohydrodynamic Waves from Colliding Flows in the Solar Corona
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DOI：
10.3847/2041-8213/aacf98
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发表时间：
2018-07
期刊：
影响因子：
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通讯作者：
P. Antolin;P. Pagano;I. De Moortel;V. Nakariakov
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文献类型：
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作者：
P. Antolin;P. Pagano;I. De Moortel;V. Nakariakov
横向磁流体动力学（MHD）波渗透太阳大气，是日冕加热的候选者。然而，这些波的起源仍然不清楚。在这封信中，我们分析了日珥/太阳光学望远镜（SOT）和界面区域成像光谱仪（IRIS）在太阳边缘的日珥/日冕雨环状结构的协调观测。沿结构沿着观察到冷而密集的下行流和上行流。观测到一个向下和向上的气流之间的碰撞，估计能量通量为107-108 erg cm-2 s-1，产生了总振幅估计为1040 km s-1的股线振荡横向扰动，以及一个短暂的等离子体温度升高到至少105 K的增亮事件。我们解释为香肠和扭结横向MHD波的基础上的等离子体流碰撞的二维MHD模拟的响应。碰撞团块之间的长度、密度和速度差以及磁场强度是决定碰撞反应的主要参数。团块之间的不对称性（冲击表面的角度和/或流动轴线的偏移）的存在对于产生扭结模式是至关重要的。利用观测值，我们成功地再现了观测到的横向扰动和增亮，并显示了绝热加热到日冕温度。数值模拟结果表明，在这种环形结构中，等离子体β被限制在0.09 ~ 0.36之间。这些结果表明，这种碰撞从逆流流可以在原位横向MHD波的来源，并为冷和密集的突出条件，这样的波可能有显着的振幅。
Transverse magnetohydrodynamic (MHD) waves permeate the solar atmosphere and are a candidate for coronal heating. However, the origin of these waves is still unclear. In this Letter, we analyze coordinated observations from Hinode/Solar Optical Telescope (SOT) and Interface Region Imaging Spectrograph (IRIS) of a prominence/coronal rain loop-like structure at the limb of the Sun. Cool and dense downflows and upflows are observed along the structure. A collision between a downward and an upward flow with an estimated energy flux of 107–108 erg cm−2 s−1 is observed to generate oscillatory transverse perturbations of the strands with an estimated ≈40 km s−1 total amplitude, and a short-lived brightening event with the plasma temperature increasing to at least 105 K. We interpret this response as sausage and kink transverse MHD waves based on 2D MHD simulations of plasma flow collision. The lengths, density, and velocity differences between the colliding clumps and the strength of the magnetic field are major parameters defining the response to the collision. The presence of asymmetry between the clumps (angle of impact surface and/or offset of flowing axis) is crucial for generating a kink mode. Using the observed values, we successfully reproduce the observed transverse perturbations and brightening, and show adiabatic heating to coronal temperatures. The numerical modeling indicates that the plasma β in this loop-like structure is confined between 0.09 and 0.36. These results suggest that such collisions from counter-streaming flows can be a source of in situ transverse MHD waves, and that for cool and dense prominence conditions such waves could have significant amplitudes.