Helical magnetic fields in filaments

Rust, David M.; Kumar, Ashok

doi:10.1007/bf00670732

Cited by 363 publications

(261 citation statements)

References 40 publications

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“…17 (adapted from Bothmer and Schwenn, 1994): four di erent magnetic ux tubes are expected in interplanetary space from the magnetic structure of disappearing ®laments in the Sun's southern and northern hemispheres. The results indicate that the magnetic helicity of MCs observed in interplanetary space is the same as that of the associated ®laments, i.e., the magnetic helicity inherent in magnetic ®elds at the Sun might be conserved outward into interplanetary space, as has been pointed out by Rust and Kumar (1994b) in agreement with ®ndings of helicity conservation in laboratory plasmas. Note that on the contrary, Martin and McAllister (1997) claimed that the helicity of the overlying arches above a prominence axis which may evolve into¯ux tube is opposite to that of the ®lament beneath it.…”

Section: Expansion Of Magnetic Cloudssupporting

confidence: 83%

The structure and origin of magnetic clouds in the solar wind

1998

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Abstract. Plasma and magnetic ®eld data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs) in the inner heliosphere. 46 MCs were identi®ed in the Helios data for the period 1974±1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections). Seven MCs were identi®ed as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs) identi®ed as whitelight brightness enhancements in the Helios photometer data. The total (plasma and magnetic ®eld) pressure in MCs was higher and the plasma-b lower than in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as largescale quasi-cylindrical magnetic¯ux tubes. The axes of the¯ux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale¯ux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to $ 60 in solar longitude in the ecliptic having the same magnetic con®guration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R 0X8 (R in AU). The density decrease inside MCs was found to be proportional to R À2X4 , thus being stronger compared to the average solar wind. Four di erent magnetic con®gurations, as expected from the¯ux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with leftand right-handed magnetic helicity occurred with about equal frequencies during 1974±1981, but surprisingly, the majority (74%) of the MCs had a south to north (SN) rotation of the magnetic ®eld vector relative to the ecliptic. In contrast, an investigation of solar wind data obtained near Earth's orbit during 1984±1991 showed a preference for NS-clouds. A direct correlation was found between MCs and large quiescent ®lament disappearances (disparition brusques, DBs). The magnetic con®gurations of the ®laments, as inferred from the orientation of the prominence axis, the polarity of the overlying ®eld lines and the hemispheric helicity pattern observed for ®laments, agreed well with the in situ observed magnetic structure of the associated MCs. The results support the model of MCs as large-scale expanding quasi-cylindrical magnetic¯ux tubes in the solar wind, most likely caused by SMEs associated with eruptions of large quiescent ®laments. We suggest that the hemispheric dependence of the magnetic helicity structure observed for solar ®laments can explain the preferred orientation of MCs in interplanetary space as well as their solar cycle behavior. However, the whitelight features of SMEs and the measured volumes of their interplanetary coun...

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Section: Expansion Of Magnetic Cloudssupporting

confidence: 83%

The structure and origin of magnetic clouds in the solar wind

1998

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“…A similar process of flux and helicity ejection was made independently by Rust [1994] Figure 9 shows that the rise of a magnetic flux rope through the photosphere must involve the latter process; that is, it is associated with flux removal from the photosphere. In the more common process of a field churned into a complicated tangle, the rise of the magnetic system through the photosphere involves a complexity of smallscale U-loops lifting off through the photosphere.…”

Section: Cmes and The Solar Dynamomentioning

confidence: 65%

Coronal mass ejections, magnetic flux ropes, and solar magnetism

Low¹

2001

J. Geophys. Res.

377

272

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Abstract. This review on coronal mass ejections (CMEs) treats hydromagnetic issues posed by observations, in order to relate CMEs to flares and prominence eruptions and to consider the roles these processes play in the evolution of the solar corona in the course of an l 1-year cycle. This global view of the corona, proposed in varying degrees of completeness by the author, physically connects the corona to the photosphere and the dynamo in the solar interior. This view is synthesized afresh starting with CME phenomenology, in order to include some new insights and to arrive at definite statements on the hydromagnetic nature of CMEs. The synthesis shows that each CME culminates a long, coherent physical process involving magnetic-flux emergence; flares and magnetic reconnection; creation of long-lived, large-scale coronal structures; conservation of magnetic helicity; and failure of confinement of magnetic flux ropes in the open atmosphere. Each CME contributes a systematic permanent change to the coronal magnetic field. In this view the cumulative changes brought by all the CMEs in the course of a solar cycle have fundamental implications for the magnetic-flux budgets of the photosphere and the corona.

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“…The eruption of the flux rope occurs in response to the injection of magnetic flux into the rope. It is however unanswered to date whether the flux rope emerges from below the photosphere (Rust and Kumar 1994) or if it is formed above the photosphere (e.g., Gosling et al 1995). Contrarily, other authors (e.g., Forbes and Priest 1995;Shibata 2001) assume a loop arcade-like structure.…”

Section: -D Structure Of Cmes Projection Effects and Halo Cmesmentioning

confidence: 99%

Solar Weather Event Modelling and Prediction

et al. 2009

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Key drivers of solar weather and mid-term solar weather are reviewed by considering a selection of relevant physics-and statistics-based scientific models as well as a selection of related prediction models, in order to provide an updated operational scenario for space weather applications. The characteristics and outcomes of the considered scientific and prediction models indicate that they only partially cope with the complex nature of solar activity for the lack of a detailed knowledge of the underlying physics. This is indicated by the fact that, on one hand, scientific models based on chaos theory and non-linear dynamics reproduce better the observed features, and, on the other hand, that prediction models based on statistics and artificial neural networks perform better. To date, the solar weather prediction success at most time and spatial scales is far from being satisfactory, but the forthcoming ground-and space-based high-resolution observations can add fundamental tiles to the modelling and predicting frameworks as well as the application of advanced mathematical approaches in the analysis of diachronic solar observations, that are a must to provide comprehensive and homogeneous data sets.

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Helical magnetic fields in filaments

Cited by 363 publications

References 40 publications

The structure and origin of magnetic clouds in the solar wind

The structure and origin of magnetic clouds in the solar wind

Coronal mass ejections, magnetic flux ropes, and solar magnetism

Solar Weather Event Modelling and Prediction

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