Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh11a0701r&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SH11A-0701
Physics
7509 Corona, 7529 Photosphere, 7549 Ultraviolet Emissions, 7839 Nonlinear Phenomena, 7871 Waves And Instabilities
Scientific paper
A regular pattern having a braided appearance was discovered (Shine, 1999) while sampling ``space-time'' slices in the TRACE Fe IX/X 171 Å and Fe 195 Å data cubes corresponding to spongy EUV coronal emission at temperatures of about 106 ~K. Such emission, associated with some plages could be categorized as the ``moss'' - a low lying (2-4 Mm above the photosphere) hot ``clouds'' with finite thickness and short time-scale variation of brightness (Berger at al., 1999, ApJ, 519, L97). Here we use the time series of the EUV TRACE images (with ~= 40 ~s cadence) co-aligned with the high resolution MDI magnetograms of 270"x166" area containing three sunspots and several plages. We show that spongy EUV emission always exists over and mimics the plage regions that are dominated by one polarity magnetic elements. Space-time slices show coherent braid-like structures with almost constant period for a given area. The braid period varies slightly for different emission regions ranging from 3 min to 10 min and depends mainly on the magnetic filling of the underlying plage (the observation time is over 3 h). We propose a mechanism to explain the observed properties of a ``meandering moss'' based on the idea that a highly dynamic ensemble of magnetic flux tubes is energetically open system with the source of the energy, dispersion and dissipation. The unsteady wave packets generated here are subject of modulation instabilities because of stratification and transverse inhomogeneity of the medium (magnetic filling factor in pages is f ~ 0.3). This leads to nonlinear self-organization of a system in higher layers of atmosphere which manifest itself in periodically spaced regions of enhanced brightening forming braid structures in time. The solution for dynamic coherent structures in the enhanced emission is similar to N-soliton solution of the modified KdV equation, and contains the observable parameters that makes quantitative analysis quite reliable. These structures, once formed, are known to exist as long as the source and a sink of energy remain in place.
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