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On the twists of interplanetary magnetic flux ropes observed at 1 AU 的详细信息
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名称
On the twists of interplanetary magnetic flux ropes observed at 1 AU
所属服务系统
空间科学主题数据库
URI
cn.csdb.space.201706187
作者姓名
Yuming Wang
作者单位
University of Science and Technology of China
摘要
Magnetic flux ropes (MFRs) are one kind of fundamental structures in the solar physics, and involved in various eruption phenomena. Twist, characterizing how the magnetic field lines wind around a main axis, is an intrinsic property of MFRs, closely related to the magnetic free energy and stableness. So far it is unclear how much amount of twist is carried by MFRs in the solar atmosphere and in heliosphere and what role the twist played in the eruptions of MFRs. Contrasting to the solar MFRs, there are lots of insitu measurements of magnetic clouds (MCs), the largescale MFRs in interplanetary space, providing some important information of the twist of MFRs. Thus, starting from MCs, we investigate the twist of interplanetary MFRs with the aid of a velocitymodified uniformtwist forcefree flux rope model. It is found that most of MCs can be roughly fitted by the model and nearly half of them can be fitted fairly well though the derived twist is probably overestimated by a factor of 2.5. By applying the model to 115 MCs observed at 1 AU, we find that (1) the twist angles of interplanetary MFRs generally follow a trend of about $0.6\frac{l}{R}$ radians, where $\frac{l}{R}$ is the aspect ratio of a MFR, with a cutoff at about $12\pi$ radians AU$^{1}$, (2) most of them are significantly larger than $2.5\pi$ radians but well bounded by $2\frac{l}{R}$ radians, (3) strongly twisted magnetic field lines probably limit the expansion and size of MFRs, and (4) the magnetic field lines in the legs wind more tightly than those in the leading part of MFRs. These results not only advance our understanding of the properties and behavior of interplanetary MFRs, but also shed light on the formation and eruption of MFRs in the solar atmosphere. A discussion about the twist and stableness of solar MFRs are therefore given.
关键词
Magnetic flux ropes, Twist, Coronal mass ejections, Magnetic clouds, Unstable
备注
文献出处
J. Geophys. Res., 121, DOI:10.1002/2016JA023075,2016.
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