On the twists of interplanetary magnetic flux ropes observed at 1 AU. Issue 10 (18th October 2016)

• Record Type: Journal Article
• Authors: Wang, Yuming; Zhuang, Bin; Hu, Qiang; Liu, Rui; Shen, Chenglong; Chi, Yutian
• Is Part Of: Journal of geophysical research. Volume 121:Issue 10(2016:Oct.)
• Page Start: 9316
• Page End: 9339
• Publication Date: 2016-10-18
• Subjects: Magnetic flux ropes -- Twist -- Coronal mass ejections -- Magnetic clouds -- Unstable; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023075
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Magnetic flux ropes (MFRs) are one kind of fundamental structures in the solar/space 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. Although the effect of the twist on the behavior of MFRs had been widely studied in observations, theory, modeling, and numerical simulations, it is still 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 in situ measurements of magnetic clouds (MCs), the large‐scale 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 velocity‐modified uniform‐twist force‐free 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 l R radians, where l R is the aspect ratio of a MFR, with a cutoff at about 12 π radians AU −1, (2) most of them are significantly larger than 2.5 π radians but well bounded by 2 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. Key Points: Establish a velocity‐modified uniform‐twist force‐free flux rope model Obtain the statistical properties of the twists of interplanetary magnetic flux ropes The total twist angles of most MFRs are larger than 2.5 π but bounded by 2 times of the aspect ratio of a MFR