Journal ArticleDOI
Magnetic flux rope versus the spheromak as models for interplanetary magnetic clouds
TLDR
In this article, the authors compare and contrast two models for the global magnetic field line topology of magnetic clouds: a magnetic flux tube geometry, on the one hand, and a spheromak geometry (including possible higher multiples), on the other.Abstract:
Magnetic clouds form a subset of interplanetary ejecta with well-defined magnetic and thermodynamic properties. Observationally, it is well established that magnetic clouds expand as they propagate antisunward. The aim of this paper is to compare and contrast two models which have been proposed for the global magnetic field line topology of magnetic clouds: a magnetic flux tube geometry, on the one hand, and a spheromak geometry (including possible higher multiples), on the other. Traditionally, the magnetic structure of magnetic clouds has been modeled by force-free configurations. In a first step, we therefore analyze the ability of static force-free models to account for the asymmetries observed in the magnetic field profiles of magnetic clouds. For a cylindrical flux tube the magnetic field remains symmetric about closest approach to the magnetic axis on all spacecraft orbits intersecting it, whereas in a spheromak geometry one can have asymmetries in the magnetic field signatures along some spacecraft trajectories. The duration of typical magnetic cloud encounters at 1 AU (1 to 2 days) is comparable to their travel time from the Sun to 1 AU and thus magnetic clouds should be treated as strongly nonstationary objects. In a second step, therefore, we abandon the static approach and model magnetic clouds as self-similarly evolving MHD configurations. In our theory, the interaction of the expanding magnetic cloud with the ambient plasma is taken into account by a drag force proportional to the density and the velocity of expansion. Solving rigorously the full set of MHD equations, we demonstrate that the asymmetry in the magnetic signature may arise solely as a result of expansion. Using asymptotic solutions of the MHD equations, we least squares fit both theoretical models to interplanetary data. We find that while the central part of the magnetic cloud is adequately described by both models, the 'edges' of the cloud data are modeled better by the magnetic flux tube. Further comparisons of the two models necessarily involve thermodynamic properties, since real magnetic configurations are never exactly force-free and gas pressure plays an essential role. We consider a polytropic gas. Our theoretical analysis shows that the self-similar expansion of a magnetic flux tube requires the polytropic index gamma to be less than unity. For the spheromak, however, self-similar, radially expanding solutions are known only for gamma equal to 4/3. This difference, therefore, yields a good way of distinguishing between the two geometries. It has been shown recently that the polytropic relationship is applicable to magnetic clouds and that the corresponding polytropic index is approximately 0.5. This observational result is consistent with the self-similar model of the magnetic flux rope but is in conflict with the self-similar spheromak model.read more
Citations
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Journal ArticleDOI
The structure and origin of magnetic clouds in the solar wind
TL;DR: In this paper, the authors investigated the structure of magnetic clouds (MCs) in the inner heliosphere and found that they can best be described as large-scale quasi-cylindrical magnetic flux tubes.
Journal ArticleDOI
Interplanetary origin of geomagnetic storms
TL;DR: In this article, the authors examined the effects of a combination of a long-duration southward sheath magnetic field, followed by a magnetic cloud Bs event, and showed that double, and sometimes triple, IMF Bs events are important causes of such events.
Journal ArticleDOI
CME Theory and Models
Terry G. Forbes,Jon A. Linker,James Chen,Consuelo Cid,József Kóta,M. A. Lee,G. Mann,Zoran Mikic,M. S. Potgieter,J. M. Schmidt,George Siscoe,Rami Vainio,Spiro K. Antiochos,Pete Riley +13 more
TL;DR: In this article, the authors provide an overview of current efforts in the theory and modeling of CMEs, focusing on how energy stored in the coronal magnetic field can be released violently to drive CME driven shocks.
Book ChapterDOI
The Interplanetary Causes of Magnetic Storms: A Review
TL;DR: The dominant interplanetary phenomena causing intense magnetic storms are the remnants of fast coronal mass ejections, high-speed solar ejects as mentioned in this paper, during and a few years after solar maximum.
Journal ArticleDOI
Theory of prominence eruption and propagation: Interplanetary consequences
TL;DR: In this paper, the dynamics of solar magnetic flux ropes are investigated and the subsequent expansion of the flux rope through a model corona and solar wind is analyzed using macroscopic quantities, including the forces, apex speed and height from the Sun, and magnetic field.
References
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Journal ArticleDOI
Magnetic loop behind an interplanetary shock: Voyager, Helios and IMP-8 observations
TL;DR: The flow behind an interplanetary shock was analyzed through the use of magnetic field and plasma data from five spacecraft, with emphasis on the magnetic cloud identified by a characteristic variation of the latitude angle of the magnetic field.
Journal ArticleDOI
Interplanetary magnetic clouds At 1 AU
L. W. Klein,L. F. Burlaga +1 more
TL;DR: The magnetic field geometry in such a magnetic cloud is consistent with that of a magnetic loop, but it cannot be determined uniquely as mentioned in this paper, but it is known that at least one cloud passed the earth every 3 months, and the average expansion speed was estimated to be of the order of half the ambient Alfven speed.
Journal ArticleDOI
Magnetic field structure of interplanetary magnetic clouds at 1 AU
TL;DR: In this article, a least-squares program was developed to fit magnetic field data within a cloud, while estimating such cloud properties as its size, maximum field strength, and axis inclination.
Journal ArticleDOI
Magnetic clouds and force-free fields with constant alpha
TL;DR: In this paper, a cylindrically symmetric, constant alpha force-free magnetic field model was proposed to explain the types of variations of the magnetic field direction that are observed as a magnetic cloud moves past a spacecraft.
Book ChapterDOI
Coronal Mass Ejections and Magnetic Flux Ropes in Interplanetary Space
TL;DR: In this article, it is suggested that interplanetary magnetic flux ropes form as a result of reconnection within rising, previously sheared coronal magnetic loops, indicating closed field structures that are either rooted at both ends in the sun or entirely disconnected from it.