Global axis shape of magnetic clouds deduced from the distribution of their local axis orientation
Global axis shape of magnetic clouds deduced from the distribution of their local axis orientation
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DOI：
10.1051/0004-6361/201321442
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发表时间：
2013-05
影响因子：
6.5
通讯作者：
M. Janvier;P. Démoulin;S. Dasso
中科院分区：
文献类型：
--
作者：
M. Janvier;P. Démoulin;S. Dasso
上下文日冕物质抛射（CME）是行星际空间中的常规成像仪跟踪，而磁云（MC）的性质是由航天器本地测量。然而，无论是成像仪和原位数据不提供直接估计的全球磁绳属性。目标。本研究的主要目的是约束的全球形状的磁绳轴从本地测量，并比较结果从原位数据与成像仪观测。方法.我们进行了统计分析的一组MC观测的风航天器在地球附近超过15年。我们分析了不同MC参数之间的相关性，并研究了定义局部轴方向的角度的统计分布。假设有一个样本的MC与航天器穿过沿着其轴的均匀分布，我们表明，平均轴形状可以从轴的方向分布。作为补充，虽然日光层成像仪通常不观察MC，但只有他们的鞘区，我们分析了一个事件，其中的磁通绳轴可以从立体声成像仪估计。结果从一组理论模型的分析，我们表明，局部轴方向的分布强烈地受到全局轴形状的影响。接下来，我们从观察到的取向分布的积分中导出平均轴形状。这种形状是稳健的，因为它主要是根据分布的全局形状确定的。此外，我们发现没有依赖于黄道上的磁通绳倾角。最后，得出的形状是完全一致的，从2008年6月事件的日光层成像仪观测。结论.我们导出了MC轴的平均形状，它只依赖于一个自由参数，角分离的腿（从太阳上看）。这种平均形状可以用于各种背景，例如高能粒子的研究或空间天气预报。
Context. Coronal mass ejections (CMEs) are routinely tracked with imagers in the interplanetary space while magnetic clouds (MCs) properties are measured locally by spacecraft. However, both imager and in situ data do not provide direct estimation on the global flux rope properties. Aims. The main aim of this study is to constrain the global shape of the flux rope axis from local measurements, and to compare the results from in-situ data with imager observations. Methods. We perform a statistical analysis of the set of MCs observed by WIND spacecraft over 15 years in the vicinity of Earth. We analyze the correlation between di erent MC parameters and study the statistical distributions of the angles defining the local axis orientation. With the hypothesis of having a sample of MCs with a uniform distribution of spacecraft crossing along their axis, we show that a mean axis shape can be derived from the distribution of the axis orientation. In complement, while heliospheric imagers do not typically observe MCs but only their sheath region, we analyze one event where the flux-rope axis can be estimated from the STEREO imagers. Results. From the analysis of a set of theoretical models, we show that the distribution of the local axis orientation is strongly a ected by the global axis shape. Next, we derive the mean axis shape from the integration of the observed orientation distribution. This shape is robust as it is mostly determined from the global shape of the distribution. Moreover, we find no dependence on the flux-rope inclination on the ecliptic. Finally, the derived shape is fully consistent with the one derived from heliospheric imager observations of the June 2008 event. Conclusions. We have derived a mean shape of MC axis which only depends on one free parameter, the angular separation of the legs (as viewed from the Sun). This mean shape can be used in various contexts such as the study of high energy particles or space weather forecast.