Analysis of Deformation and Erosion during CME Evolution
Analysis of Deformation and Erosion during CME Evolution
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DOI：
10.3390/geosciences11080314
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发表时间：
2021-08-01
期刊：
影响因子：
2.7
通讯作者：
Poedts, Stefaan
中科院分区：
文献类型：
--
作者：
Hosteaux, Skralan;Chane, Emmanuel;Poedts, Stefaan
磁化日冕物质抛射（CME）在从太阳到地球的过程中会发生相当大的变形。此外，它们的内部磁场与周围太阳风磁场的相互作用会导致它们的质量和磁通量发生偏转和侵蚀。在这里，我们分析轴对称（2.5D）MHD模拟的正常和逆CME，即，与背景太阳风的极性相反或相同，并试图量化的侵蚀和不同的力量，在其演变过程中对日冕物质抛射。通过对这些力的分析，发现背景风密度的增加导致鞘层中更强的等离子体压力梯度，从而使磁云减速更多。这反过来又导致磁云中心和分界线之间的磁压梯度增加，导致进一步减速。无论极性如何，在我们的模型中，在CME的后部和头盔流光的闭合场线之间形成的电流片导致磁场线从磁云中剥离。研究还发现，无论背景风密度如何，缓慢的正常CME都会经历相同的侵蚀量。此外，随着初始风速的增大，风速对侵蚀的影响也增大。我们发现，增加日冕物质抛射的速度导致更高的整体侵蚀，由于更强的磁场重联。对于逆日冕物质抛射，磁力线没有被剥离，而是被添加到磁云中，导致在1 Au处的磁通量是具有相同初始通量的正常日冕物质抛射的两倍。
Magnetised coronal mass ejections (CMEs) are quite substantially deformed during their journey form the Sun to the Earth. Moreover, the interaction of their internal magnetic field with the magnetic field of the ambient solar wind can cause deflection and erosion of their mass and magnetic flux. We here analyse axisymmetric (2.5D) MHD simulations of normal and inverse CME, i.e., with the opposite or same polarity as the background solar wind, and attempt to quantify the erosion and the different forces that operate on the CMEs during their evolution. By analysing the forces, it was found that an increase of the background wind density results in a stronger plasma pressure gradient in the sheath that decelerates the magnetic cloud more. This in turn leads to an increase of the magnetic pressure gradient between the centre of the magnetic cloud and the separatrix, causing a further deceleration. Regardless of polarity, the current sheet that forms in our model between the rear of the CME and the closed field lines of the helmet streamer, results in magnetic field lines being stripped from the magnetic cloud. It is also found that slow normal CMEs experience the same amount of erosion, regardless of the background wind density. Moreover, as the initial velocity increases, so does the influence of the wind density on the erosion. We found that increasing the CME speed leads to a higher overall erosion due to stronger magnetic reconnection. For inverse CMEs, field lines are not stripped away but added to the magnetic cloud, leading to about twice as much magnetic flux at 1 AU than normal CMEs with the same initial flux.