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Upflows in funnel-like legs of coronal magnetic loops | | Hui Tian
; Eckart Marsch
; Werner Curdt
; Jiansen He
; | | Date: |
3 Sep 2009 | | Abstract: | The prominent blue shifts of Ne viii associated with the junctions of the
magnetic network in the quiet Sun are still not well understood. By comparing
the coronal magnetic-field structures as obtained by a potential-field
reconstruction with the conspicuous blue-shift patches on the dopplergram of Ne
viii as observed in an equatorial quiet-Sun region, we find that most of the
regions with significant upflow are associated with the funnel-like legs of
magnetic loops and co-spatial with increments of the line width. These
quasi-steady upflows can be regarded as the signatures of mass supply to
coronal loops. By using the square-root of the line intensity as a proxy for
the plasma density, the mass flux of the upflow in each funnel can be
estimated. We find that the mass flux is anti-correlated with the funnel’s
expansion factor as determined from the extrapolated magnetic field. One of the
loop systems is associated with a coronal bright point, which was observed by
several instruments and exhibited various morphologies in different wavelengths
and viewing directions. A remarkable agreement between its magnetic structure
and the associated EUV emission pattern was found, suggesting an almost
potential-field nature of the coronal magnetic field. We also report the direct
detection of a small-scale siphon flow by both STEREO satellites. However, this
transient siphon flow occurred in a weak mixed-polarity-field region, which was
outside the adjacent magnetic funnel, and thus it is perhaps not related to
plasma upflow in the funnel. Based on these observations, we suggest that at
upper-TR temperatures the dominant flows in quiet-Sun coronal loops are
long-lasting upflows rather than siphon flows. We also discuss the implications
for coronal heating and unresolved magnetic structures. | | Source: | arXiv, 0909.0739 | | Services: | Forum | Review | PDF | Favorites | |
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