DERIVING THE PROPERTIES OF CORONAL PRESSURE FRONTS IN 3D: APPLICATION TO THE 2012 MAY 17 GROUND LEVEL ENHANCEMENT
DERIVING THE PROPERTIES OF CORONAL PRESSURE FRONTS IN 3D: APPLICATION TO THE 2012 MAY 17 GROUND LEVEL ENHANCEMENT
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DOI：
10.3847/1538-4357/833/1/45
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
A. Rouillard;I. Plotnikov;R. Pinto;M. Tirole;M. Lavarra;P. Zucca;R. Vainio;A. Tylka;A. Vourlidas-A.
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作者：
A. Rouillard;I. Plotnikov;R. Pinto;M. Tirole;M. Lavarra;P. Zucca;R. Vainio;A. Tylka;A. Vourlidas-A.
我们研究了在2012年5月17日地面增强期间在地球附近测量到的日冕激波和高能粒子之间的联系。我们开发了一种基于多点成像的新技术来三角测量日冕中激波形成的三维（3D）膨胀。它使用来自三个有利位置的图像，绘制受压力锋干扰的日冕区域的最外层范围。我们首次导出了整个锋面的三维速度矢量和马赫数随时间的分布。我们的方法使用了日冕磁场重建、全磁流体动力学模拟和成像反演技术。我们发现，在日冕物质抛射开始的几分钟内，最高的MFM值出现在日冕中性线附近；这条中性线通常与日球层电流和等离子体片的来源有关。我们说明了激波速度、激波几何形状和马赫数沿不同的模拟磁力线的可变性。尽管激波马赫数的推导存在一定程度的不确定性，但所有采用的重建技术都表明，GeV粒子的释放时间发生在日冕激波达到超临界（MFM bbbb3）时。结合现场测量和日球层图像，我们还证明了加速器（2012年5月17日的日冕冲击）和近地环境之间的磁连接是通过大约5天前从同一活跃区域喷发的磁云建立的。
We study the link between an expanding coronal shock and the energetic particles measured near Earth during the ground level enhancement of 2012 May 17. We developed a new technique based on multipoint imaging to triangulate the three-dimensional (3D) expansion of the shock forming in the corona. It uses images from three vantage points by mapping the outermost extent of the coronal region perturbed by the pressure front. We derive for the first time the 3D velocity vector and the distribution of Mach numbers, MFM, of the entire front as a function of time. Our approach uses magnetic field reconstructions of the coronal field, full magnetohydrodynamic simulations and imaging inversion techniques. We find that the highest MFM values appear near the coronal neutral line within a few minutes of the coronal mass ejection onset; this neutral line is usually associated with the source of the heliospheric current and plasma sheet. We illustrate the variability of the shock speed, shock geometry, and Mach number along different modeled magnetic field lines. Despite the level of uncertainty in deriving the shock Mach numbers, all employed reconstruction techniques show that the release time of GeV particles occurs when the coronal shock becomes super-critical (MFM > 3). Combining in situ measurements with heliospheric imagery, we also demonstrate that magnetic connectivity between the accelerator (the coronal shock of 2012 May 17) and the near-Earth environment is established via a magnetic cloud that erupted from the same active region roughly five days earlier.