Apparent and Intrinsic Evolution of Active Region Upflow using Hinode/EIS

BAKER, D.; JANVIER, M.; DÉMOULIN, P.; MANDRINI, C.H.

Congreso; Hinode 9 International Science Meeting; 2015

We analyze the evolution of Fe XII coronal plasma upflows from the edges of 10 active regions (AR) as they cross the solar disk using Hinode's EUV Imaging Spectrometer (EIS).  Confirming the results of Demoulin et al 2013 (Sol. Phys, 283, 341), we find that for each AR there is an observed long term evolution of the upflows which is largely due to the solar rotation progressively changing the viewpoint of dominantly stationary upflows.  From this projection effect we estimate the unprojected upflow velocity and its inclination to the local vertical.  We find AR upflows typically fan away from the AR core by 10 to 40 degrees both for the following and leading upflows.  On top of this dominant apparent evolution we identify an intrinsic evolution of the upflows due to coronal activity which is AR dependent. Further, line widths are correlated with Doppler velocities only for the few ARs having the largest velocities.  We conclude that the spatial gradient of the upflow velocities must be large enough to imply a line broadening above the thermal line width of Fe XII. Finally, for AR11575, upflow evolution is clearly observed occurring in multiple locations by pairs.  This is important for constraining the upflow driving mechanism as this implies that the mechanism is not a local one occurring over one polarity.  AR upflows originating from reconnections along quasi-separatrix layers (QSLs) between over-pressure AR loops and neighboring under-pressure loops is consistent with upflows occurring in pairs unlike proposed mechanisms such as nano-flares and wave impulse absorption.