Physics
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.8109m&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #81.09; Bulletin of the American Astronomical Society, Vol. 24, p.1253
Physics
Scientific paper
The soft X-ray telescope on the Yohkoh mission enabled us to observe the evolution of emerging flux regions (EFR) in coronal X-rays with high spatial and temporal resolution. Furthermore, we now have enough computing capability to perform three-dimensional MHD simulation of EFRs with sufficient spacial resolution to study details of the flux emergence process. These new tools provide the opportunity to investigate the physics involved in the formation of coronal loops in much more detail. We carried out 3D MHD simulations of emerging magnetic flux regions under various intial conditions; (1) a horizontal magnetic flux sheet, (2) a bundle of horizontal flux tubes, and (3) a flux sheet with sheared magnetic fields. Numerical results show that coronal magnetic loops are formed due to the enhanced buoyancy resulting from gas precipitating along magnetic field lines. The interchange modes help to produce a fine fibrous structure perpendicular to the magnetic field direction in the linear stage, while the undular modes determine the overall loop structure. We observe in 3D simulations that during the ascendance of loops the bundle of flux tubes, or even the flux sheet, developes into dense filaments pinched between magnetic loops. We also find that magnetic field lines are twisted by the vortex motion produced by the horizontal expansion of magnetic loops. Our numerical results may explain the observed signatures such as (1) the spacial relation between soft X-ray loops and Hα arch filaments obtained by coordinated observation between Yohkoh and ground-based observatories (Kawai et al. 1992), (2) the rate of increase in size of soft X-ray loops in EFRs (Ishido et al. 1992), (3) emergence of twisted magnetic loops, and (4) the threshold flux for formation of chromospheric arch filament systems (AFS).
Acton L. L.
Akioka Maki
Ishido Yoshinori
Kaisig Michael
Kawai Goro
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