Bin Zhuang

On the twists of interplanetary magnetic flux ropes observed at 1 AU

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 over-estimated 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 0.6lR radians, where lR is the aspect ratio of a MFR, with a cutoff at about 12π radians AU−1, (2) most of them are significantly larger than 2.5π radians but well bounded by 2lR 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.

On the propagation of a geoeffective coronal mass ejection during 15-17 March 2015

The largest geomagnetic storm so far in the solar cycle 24 was produced by a fast coronal mass ejection (CME) originating on 2015 March 15. It was an initially west-oriented CME and expected to only cause a weak geomagnetic disturbance. Why did this CME finally cause such a large geomagnetic storm? We try to find some clues by investigating its propagation from the Sun to 1 AU. First, we reconstruct the CMEs kinematic properties in the corona from the SOHO and SDO imaging data with the aid of the graduated cylindrical shell (GCS) model. It is suggested that the CME propagated to the west

A statistical study of the likelihood of a super geomagnetic storm occurring in a mild solar cycle

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The Significance of the Influence of the CME Deflection in Interplanetary Space on the CME Arrival at Earth

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Reconstructing Solar Wind Inhomogeneous Structures From Stereoscopic Observations in White Light: Small Transients Along the Sun-Earth Line

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The Role of Viscosity in Causing the Plasma Poloidal Motion in Magnetic Clouds

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Forecast Coronal Mass Ejection Arrival at the Earth: An Integrated Automated System and Its Performance

away from the Sun-Earth line with a speed of about 817 km s