Flux Rope Configuration Research Articles

On the magnetic topology of October/November 2003 events

We examine the topology of several magnetic ejecta events during October–November 2003. The Grad‐Shafranov reconstruction results from ACE magnetic and plasma data show magnetic flux rope configurations. Some are large scale, with sizes of tenths of an AU, typical of magnetic clouds. Some are of sizes hundredths of an AU. Their characteristic parameters are reported. Magnetic field data from Wind spacecraft are utilized to compare the prediction from numerical modeling with the actual measurement. Poor to good agreement is achieved. The deviations are discussed, particularly in the context of extremely high‐speed solar wind flows.

Multiple flux rope magnetic ejecta in the solar wind

Four magnetic flux rope events observed by Advanced Composition Explorer (ACE) in the solar wind at 1 AU are examined by the Grad‐Shafranov reconstruction technique. Their 2D cross sections obtained from magnetic field and plasma measurements show configurations of multiple, nonsymmetric, cylindrical flux ropes embedded within their boundaries. Each boundary is defined in consistency with two‐dimensional magnetohydrostatic theory. Among the four events, three have double flux rope configurations, and the fourth is a triplet. Parameters characterizing the events are derived. The orientation of cylindrical axis is obtained, and associated uncertainty is estimated. All events have unidirectional axial magnetic field and axial currents. The total axial magnetic flux is of the order ∼1012 Wb, and the total axial current is of the order ∼108 A. Each flux rope in the doubled flux rope pair and the triplet has the same chirality as its partner(s). Magnetic X points are formed between adjacent flux ropes on the plane perpendicular to the cylindrical axis. One event with abrupt change in magnetic field direction and another related to energetic particles are discussed.

A Three-dimensional Flux Rope Model for Coronal Mass Ejections Based on a Loss of Equilibrium

A series of simulation runs are carried out to investigate the loss of equilibrium of the three-dimensional flux rope configuration of Titov & Demoulin as a suitable mechanism for the initiation of coronal mass ejections. By means of these simulations, we are able to determine the conditions for which stable equilibria no longer exist. Our results imply that it is possible to achieve a loss of equilibrium even though the ends of the flux rope are anchored to the solar surface. However, in order to have the flux rope escape, it is necessary to modify the configuration by eliminating the arcade field.

Turbulence in coronal mass ejections

The magnetic fields measured by the ISEE 3 spacecraft are used to study MHD turbulence within coronal mass ejections (CMEs). The spectral indices of the turbulence inside CMEs are compared with spectral indices found in solar wind undisturbed by CMEs. Irrespective of the CME velocities, the spectra within CMEs are found to differ from those determined for the fast solar wind from coronal holes. Instead, the CME spectra more closely resemble those found in the slow solar wind. Since both CMEs and the plasma sheet are associated with closed magnetic structures in the solar corona, it appears that the turbulence in the solar wind arising from closed coronal regions is fundamentally different from the turbulence in wind from coronal holes. Helical properties of magnetic fields within CMEs at different scales are studied. Preliminary results indicate that, in small scales, helical fields are distributed in a random fashion with alternating signs of twisting structures. In addition however, CMEs have largescale helical structures. In the case of the magnetic cloud of day 302, 1978 this structure is interpreted as a part of the helical structure identified previously by fitting the data to a force‐free flux rope configuration.

ISEE 3 observations of plasmoids with flux rope magnectic topologies

This paper reports new evidence for the existence of plasmoids with force‐free flux rope magnetic topologies. Motivated by the fact that force‐free magnetic flux ropes have intense axial fields at their centers, the ISEE 3 observations have been searched for plasma sheet intervals in which the magnetic field intensity exceeds that in the lobes by ≥10% for a minute or longer. A total of 39 “high field regions” were found which met this simple criterion. Further examination showed that they nearly always correspond to the core regions of plasmoids; i.e, intervals of bipolar Bz with durations of minutes, fast tailward flows and clear substorm associations. A new, more realistic plasmoid magnetic field model which represents the core region as a non‐linear force‐free flux rope was developed and validated using these events. Finally, observations suggesting that plasmoids evolve toward quasi‐force‐free flux rope configurations as they move down the tail are presented.