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Title: Helicity transformation under the collision and merging of two magnetic flux ropes

 [1]; ORCiD logo [1]
  1. Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA
Publication Date:
Sponsoring Org.:
OSTI Identifier:
Grant/Contract Number:
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 7; Related Information: CHORUS Timestamp: 2018-02-15 00:20:47; Journal ID: ISSN 1070-664X
American Institute of Physics
Country of Publication:
United States

Citation Formats

DeHaas, Timothy, and Gekelman, Walter. Helicity transformation under the collision and merging of two magnetic flux ropes. United States: N. p., 2017. Web. doi:10.1063/1.4991413.
DeHaas, Timothy, & Gekelman, Walter. Helicity transformation under the collision and merging of two magnetic flux ropes. United States. doi:10.1063/1.4991413.
DeHaas, Timothy, and Gekelman, Walter. 2017. "Helicity transformation under the collision and merging of two magnetic flux ropes". United States. doi:10.1063/1.4991413.
title = {Helicity transformation under the collision and merging of two magnetic flux ropes},
author = {DeHaas, Timothy and Gekelman, Walter},
abstractNote = {},
doi = {10.1063/1.4991413},
journal = {Physics of Plasmas},
number = 7,
volume = 24,
place = {United States},
year = 2017,
month = 7

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on July 5, 2018
Publisher's Accepted Manuscript

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  • We describe the evolution and the magnetic helicity flux for two active regions (ARs) since their appearance on the solar disk: NOAA 11318 and NOAA 11675. Both ARs hosted the formation and destabilization of magnetic flux ropes. In the former AR, the formation of the flux rope culminated in a flare of C2.3 GOES class and a coronal mass ejection (CME) observed by Large Angle and Spectrometric Coronagraph Experiment. In the latter AR, the region hosting the flux rope was involved in several flares, but only a partial eruption with signatures of a minor plasma outflow was observed. We foundmore » a different behavior in the accumulation of the magnetic helicity flux in the corona, depending on the magnetic configuration and on the location of the flux ropes in the ARs. Our results suggest that the complexity and strength of the photospheric magnetic field is only a partial indicator of the real likelihood of an AR producing the eruption of a flux rope and a subsequent CME.« less
  • Spacecraft observations suggest that flux transfer events and interplanetary magnetic clouds may be associated with magnetic flux ropes which are magnetic flux tubes containing helical magnetic field lines. In the magnetic flux ropes, the azimuthal magnetic field (B{sub {theta}}) is superposed on the axial field (B{sub z}). In this paper the time evolution of a localized magnetic flux rope is studied. A two-dimensional compressible magnetohydrodynamic simulation code with a cylindrical symmetry is developed to study the wave modes associated with the evolution of flux ropes. It is found that in the initial phase both the fast magnetosonic wave and themore » Alfven wave are developed in the flux rope. After this initial phase, the Alfven wave becomes the dominant wave mode for the evolution of the magnetic flux rope and the radial expansion velocity of the flux rope is found to be negligible. Numerical results further show that even for a large initial azimuthal component of the magnetic field (B{sub {theta}} {approx equal} 1-4 B{sub z}) the propagation velocity along the axial direction of the flux rope remains to be the Alfven velocity. Diagnoses show that after the initial phase the transverse kinetic energy equals the transverse magnetic energy, which is characteristic of the Alfven mode. It is also found that the localized magnetic flux rope tends to evolve into two separate magnetic ropes propagating in opposite directions. The simulation results are used to study the evolution of magnetic flux ropes associated with flux transfer events observed at the Earth's dayside magnetopause and magnetic clouds in the interplanetary space.« less
  • At the dayside magnetopause, magnetic flux ropes can form as a result of multiple X line reconnection. In this process the presence of at least two parallel X lines leads to the formation of a magnetic flux rope with each additional X line giving another flux rope. For a finite extent of these X lines the magnetic flux of the flux ropes is connected to the external magnetic field on one or the other side of the current layer. In general, such a flux rope has frayed ends, i.e., magnetic flux enters the rope from the magnetospheric as well asmore » from the magnetosheath side and/or exits the rope to either side of the layer. However, it is shown that for an appropriate extent and location of two neighboring X lines, a simple magnetic topology can be expected, in which the major amount of magnetic flux of the rope is connected at each end to only one side of the current sheet. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnitic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. We discuss this process as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low-latitude boundary layer. 27 refs., 8 figs.« less
  • Using fully kinetic simulations of the island coalescence problem for a range of system sizes greatly exceeding kinetic scales, the phenomenon of flux pileup in the collisionless regime is demonstrated. While small islands on the scale of {lambda} {le} 55 ion inertial length (d{sub i}) coalesce rapidly and do not support significant flux pileup, coalescence of larger islands is characterized by large flux pileup and a weaker time averaged reconnection rate that scales as {radical}d{sub i}/{lambda} while the peak rate remains nearly independent of island size. For the largest islands ({lambda} = 100d{sub i}), reconnection is bursty and nearly shutsmore » off after the first bounce, reconnecting {approx}20% of the available flux.« less
  • We present results from three-dimensional visco-resistive magnetohydrodynamic simulations of the emergence of a convection zone magnetic flux tube into a solar atmosphere containing a pre-existing dipole coronal field, which is orientated to minimize reconnection with the emerging field. We observe that the emergence process is capable of producing a coronal flux rope by the transfer of twist from the convection zone, as found in previous simulations. We find that this flux rope is stable, with no evidence of a fast rise, and that its ultimate height in the corona is determined by the strength of the pre-existing dipole field. Wemore » also find that although the electric currents in the initial convection zone flux tube are almost perfectly neutralized, the resultant coronal flux rope carries a significant net current. These results suggest that flux tube emergence is capable of creating non-current-neutralized stable flux ropes in the corona, tethered by overlying potential fields, a magnetic configuration that is believed to be the source of coronal mass ejections.« less