The 3D Geometry of Active Region Upflows Deduced from Their Limb-to-Limb Evolution


We analyze the evolution of coronal plasma upflows from the edges of AR 10978, which has the best limb-to-limb data coverage with Hinode’s EUV Imaging Spectrometer (EIS). We find that the observed evolution is largely due to the solar rotation progressively changing the viewpoint of nearly stationary flows. From the systematic changes in the upflow regions as a function of distance from disc center, we deduce their 3D geometrical properties as inclination and angular spread in three coronal lines (Si vii, Fe xii, and Fe xv). In agreement with magnetic extrapolations, we find that the flows are thin, fan-like structures rooted in quasi separatrix layers (QSLs). The fans are tilted away from the AR center. The highest plasma velocities in these three spectral lines have similar magnitudes and their heights increase with temperature. The spatial location and extent of the upflow regions in the Si vii, Fe xii, and Fe xv lines are different owing to i) temperature stratification and ii) line of sight integration of the spectral profiles with significantly different backgrounds. We conclude that we sample the same flows at different temperatures. Further, we find that the evolution of line widths during the disc passage is compatible with a broad range of velocities in the flows. Everything considered, our results are compatible with the AR upflows originating from reconnections along QSLs between over-pressure AR loops and neighboring under-pressure loops. The flows are driven along magnetic field lines by a pressure gradient in a stratified atmosphere. Our interpretation of the above results is that, at any given time, we observe the superposition of flows created by successive reconnections, leading to a broad velocity distribution.

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The authors thank the referee for helpful comments which improved the clarity of the paper. The research leading to these results has received funding from the European Commission’s Seventh Framework Programme under the grant agreement No. 284461 (eHEROES project). LvDG’s work was supported by the Hungarian Research grant OTKA K-081421. CHM acknowledges financial support from the Argentinean grants PICT 2007-1790 (ANPCyT), UBACyT 20020100100733 and PIP 2009-100766 (CONICET). CHM is a member of the Carrera del Investigador Cientí fico (CONICET). PD and CHM thank ECOS-MINCyT for their cooperative science program A08U01.

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Correspondence to P. Démoulin.

Electronic Supplementary Material

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i_compare_SiFe_10978 (MOV 32.0 MB)

i_evolution_SiFe_10978 (MOV 24.6 MB)

iv_4panels_SiFe_10978 (MOV 74.2 MB)

iv_compare_SiFe_10978 (MOV 46.7 MB)

v_compare_SiFe_10978 (MOV 26.4 MB)

v_evolution_SiFe_10978 (MOV 22.2 MB)

i_compare_SiFe_10978 (MOV 32.0 MB)

i_evolution_SiFe_10978 (MOV 24.6 MB)

iv_4panels_SiFe_10978 (MOV 74.2 MB)

iv_compare_SiFe_10978 (MOV 46.7 MB)

v_compare_SiFe_10978 (MOV 26.4 MB)

v_evolution_SiFe_10978 (MOV 22.2 MB)

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Démoulin, P., Baker, D., Mandrini, C.H. et al. The 3D Geometry of Active Region Upflows Deduced from Their Limb-to-Limb Evolution. Sol Phys 283, 341–367 (2013) doi:10.1007/s11207-013-0234-7

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  • Active regions, magnetic fields
  • Active regions, velocity field
  • Corona, active
  • Spectral line, broadening