Planar magnetic structures in the solar wind

Abstract

A distinctive magnetic structure in which azimuthal and latitudinal angles of field vectors axe closely related to each other has been found in the interplanetary magnetic field data obtained by Sakigake at 0.8-1.0 AU. In this structure, termed a "planar magnetic structure" (PMS), the magnetic field vectors are nearly parallel to a fixed plane. This plane includes the spiral direction but is inclined to the ecliptic plane from 30 ø to 85 ø . The field vectors take almost all directions parallel to this plane. The PMS consists of several segments in which field directions are almost constant, and the segments axe separated by tangential discontinuities where directional changes of the field vector occur abruptly without showing any preferred polaxization. The ion number density, the ion temperature, and the plasma/3 tend to be higher in the PMS than in the surrounding plasma. The PMS events are cleaxly distinct from "magnetic clouds" both in the field configuration and in the plasma conditions. During the 25-month period from July 1985 to July 1987, eight PMS events with durations of several hours have been identified. The PMS events may be associated with newly emerging magnetic structure in the photosphere from which magnetic tongues are extended into interplanetaxy space. 1. netic field quite well [e.g., Behannon, 1978]. According to this model, the lines of force of the interplanetary magnetic field are parallel to an Archimedean spiral, and the north-south component of the field Bz is zero. While Parker's model can represent the average magnetic field of the solar wind, high time resolution data of the interplanetary magnetic field do not always agree with the model. Sometimes deviations of the field direction from the Archimedean spiral direction are as large as 90 ø , and the magnetic field vectors are almost perpendicular to the ecliptic plane. This raises a question about the causes of the deviation of the interplanetary magnetic field from the Archimedean spiral. Compression of the solar wind plasma associated with the steepening of high-speed streams [Rosenberg and Coleman, 1980] and draping of the field lines around a fast-moving plasmoid [Gosling and McComas, 1987; McComas et al., 1988] can generate directional changes of the magnetic field. However, nonspiral magnetic fields are not always associated with fast streams. Nonspiral fields which are not associated with fast streams can be due to transverse waves propagating in the interplanetary magnetic field. Alfv•n waves, which are often observed in interplanetary space, cause directional changes in the magnetic field [e.g., Belcher and Davis, 1971]. However, the deviations in the interplanetary magnetic field directions caused by Alfv•n waves would be limited to a finite angular range which is less than 90 ø with respect to the spiral direction even when the amplitude of the Alfv•n wave is large. Another candidate which can cause significant deviations from the spiral field observed in interplanetary space is the so-called "magnetic cloud" emitted fr...

Coronal mass ejections and their sheath regions in interplanetary space

“…The draping of the IMF is also one of the primary causes creating "planar magnetic structures" (PMSs) (e.g., Nakagawa et al 1989) within ICME sheath regions (e.g., Neugebauer et al 1993). These are periods when the variations of the magnetic field occur parallel to a single plane.…”

Evolution of Coronal Mass Ejection Morphology With Increasing Heliocentric Distance. Ii. In Situ Observations

“…The draping field lines ahead of an ICME into a plane of compression may lead to the formation of a "planar magnetic structure" (PMS). Nakagawa et al (1989) first identified them, and suggested various mechanisms for their formation. In these regions, the field lines, although variable, lie in a common plane.…”

Context and heliographic dependence of heliospheric planar magnetic structures

“…The original suggestion for the cause of PMSs was that they were signatures of the passage of the observing spacecraft through magnetic "tongues" or "islands" [Nakagawa et al, 1989]; it was suggested that these could be formed by solar reentrant loops.…”