Samanta Tanmoy, Tian Hui, Nakariakov Valery M
School of Earth and Space Sciences, Peking University, Beijing 100871, China.
Centre for Fusion, Space and Astrophysics, University of Warwick, Coventry CV47AL, United Kingdom.
Phys Rev Lett. 2019 Jul 19;123(3):035102. doi: 10.1103/PhysRevLett.123.035102.
Vortex shedding is an oscillating flow that is commonly observed in fluids due to the presence of a blunt body in a flowing medium. Numerical simulations have shown that the phenomenon of vortex shedding could also develop in the magnetohydrodynamic (MHD) domain. The dimensionless Strouhal number, the ratio of the blunt body diameter to the product of the period of vortex shedding and the speed of a flowing medium, is a robust indicator for vortex shedding, and, generally of the order of 0.2 for a wide range of Reynolds number. Using an observation from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, we report a wavelike or oscillating plasma flow propagating upward against the Sun's gravitational force. A newly formed shrinking loop in the postflare region possibly generates the oscillation of the upflow in the wake of the hot and dense loop through vortex shedding. The computed Strouhal number is consistent with the prediction from previous MHD simulations. Our observation suggests the possibility of vortex shedding in the solar corona.
涡街是一种振荡流，由于流动介质中存在钝体，在流体中普遍可见。数值模拟表明，涡街现象也可能在磁流体动力学（MHD）领域中出现。无量纲斯特劳哈尔数是钝体直径与涡街周期和流动介质速度乘积的比值，是涡街的一个可靠指标，在广泛的雷诺数范围内通常约为0.2。利用太阳动力学观测台上大气成像组件的观测结果，我们报告了一种逆着太阳引力向上传播的波状或振荡等离子体流。耀斑后区域新形成的收缩环可能通过涡街在热而致密的环尾迹中产生上升流的振荡。计算得到的斯特劳哈尔数与先前磁流体动力学模拟的预测结果一致。我们的观测表明日冕中存在涡街的可能性。
