Optimized Grad – Shafranov Reconstruction of a Magnetic Cloud Using STEREO-Wind Observations
Optimized Grad – Shafranov Reconstruction of a Magnetic Cloud Using STEREO-Wind Observations
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优化梯度 - Shafranov 使用立体风观测重建磁云
DOI：
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发表时间：
2009
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通讯作者：
J. Luhmann
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作者：
C. Möstl;C. Möstl;C. Farrugia;H. Biernat;H. Biernat;M. Leitner;E. Kilpua;A. Galvin;J. Luhmann
我们提出的结果的几何形状的磁云（MC）在2007年5月23日从风和立体观测的综合分析。我们首先应用格拉德- Shafranov重建的STEREO-A等离子体和磁场数据，提供的塑料和影响仪器。然后，我们在Wind观测的帮助下优化得到的场图，Wind观测是在云的最外边界进行的，航天器角间距为6°。对于重建参数的正确选择，如轴的方向，间隔和网格大小，我们发现在风的位置和实际观测以及一致的定时预测的磁场之间有很好的匹配。我们认为，重建捕获几乎全部范围的云的横截面。所得到的形状横向不变轴由扭曲的椭圆组成，并在运动方向上稍微变平。MC轴与黄道呈−58°，轴向场强为12 nT。我们得到集成的轴向磁通和电流的精度提高，我们对比的结果，从线性无力拟合。螺旋几何的MC与几乎恒定的扭曲（Au-1）是不符合线性无力Lundquist模型。我们还发现云是非力自由的（|J|/|J|>0.3），特别是在与尾部高速流相互作用的后部。在此基础上，提出了改进单航天器格拉德-沙夫拉诺夫重建方法的初步指导思想。结果也给了我们机会比较的CME方向推断STEREO/SECCHI观测Mierla等人。（Solar Phys.252，385，2008），其中MC的三维配置在1 Au。这产生了一个几乎径向的CME传播从太阳到地球。
We present results on the geometry of a magnetic cloud (MC) on 23 May 2007 from a comprehensive analysis of Wind and STEREO observations. We first apply a Grad – Shafranov reconstruction to the STEREO-A plasma and magnetic field data, delivered by the PLASTIC and IMPACT instruments. We then optimize the resulting field map with the aid of observations by Wind, which were made at the very outer boundary of the cloud, at a spacecraft angular separation of 6°. For the correct choice of reconstruction parameters such as axis orientation, interval and grid size, we find both a very good match between the predicted magnetic field at the position of Wind and the actual observations as well as consistent timing. We argue that the reconstruction captures almost the full extent of the cross-section of the cloud. The resulting shape transverse to the invariant axis consists of distorted ellipses and is slightly flattened in the direction of motion. The MC axis is inclined at −58° to the ecliptic with an axial field strength of 12 nT. We derive integrated axial fluxes and currents with increased precision, which we contrast with the results from linear force-free fitting. The helical geometry of the MC with almost constant twist (≈1.5 turns AU−1) is not consistent with the linear force-free Lundquist model. We also find that the cloud is non-force-free (|J⊥|/|J∥|>0.3) in about a quarter of the cloud cross sectional area, particularly in the back part which is interacting with the trailing high speed stream. Based on the optimized reconstruction we put forward preliminary guidelines for the improved use of single-spacecraft Grad – Shafranov reconstruction. The results also give us the opportunity to compare the CME direction inferred from STEREO/SECCHI observations by Mierla et al. (Solar Phys.252, 385, 2008) with the three-dimensional configuration of the MC at 1 AU. This yields an almost radial CME propagation from the Sun to the Earth.