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Title: A plasma β transition within a propagating flux rope

We present a 2.5 dimensional magnetohydrodynamic simulation of a magnetic flux rope (FR) propagating in the heliosphere and investigate the cause of the observed sharp plasma β transition. Specifically, we consider a strong internal magnetic field and an explosive fast start, such that the plasma β is significantly lower in the FR than in the sheath region that is formed ahead. This leads to an unusual FR morphology in the first stage of propagation, while the more traditional view (e.g., from space weather simulations like Enlil) of a pancake-shaped FR is observed as it approaches 1 AU. We investigate how an equipartition line, defined by a magnetic Weber number, surrounding a core region of a propagating FR, can demarcate a boundary layer where there is a sharp transition in the plasma β. The substructure affects the distribution of toroidal flux, with the majority of the flux remaining in a small core region that maintains a quasi-cylindrical structure. We quantitatively investigate a locus of points where the kinetic energy density of the relative inflow field is equal to the energy density of the transverse magnetic field (i.e., effective tension force). The simulation provides compelling evidence that at all heliocentric distances themore » distribution of toroidal magnetic flux away from the FR axis is not linear, with 80% of the toroidal flux occurring within 40% of the distance from the FR axis. Thus, our simulation displays evidence that the competing ideas of a pancaking structure observed remotely can coexist with a quasi-cylindrical magnetic structure seen in situ.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. George Mason University, Faifax, VA (United States)
  2. Space Science Division, Naval Research Laboratory, Washington, DC 20375-5352 (United States)
  3. Computational Astrophysics Laboratory, Advanced Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)
  4. Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya 464-8601 (Japan)
  5. Space Science Center and Department of Physics, University of New Hampshire, Durham, NH 03824 (United States)
  6. Institut de Recherche en Astrophysique et Plantologie, Universit de Toulouse (UPS) (France)
Publication Date:
OSTI Identifier:
22348419
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BOUNDARY LAYERS; COMPUTERIZED SIMULATION; CYLINDRICAL CONFIGURATION; DENSITY; DISTRIBUTION; ENERGY DENSITY; EXPLOSIVES; HELIOSPHERE; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; MASS; SPACE; SUN