Title: Apparent and Intrinsic Evolution of Active Region Upflows,
Abstract: We analyze the evolution of Fe XII coronal plasma upflows from the edges of
ten active regions (ARs) as they cross the solar disk using the Hinode Extreme
Ultraviolet 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. AR upflows typically fan away from the AR
core by 40 deg. to near vertical for the following polarity. The span of
inclination angles is more spread for the leading polarity with flows angled
from -29 deg. (inclined towards the AR center) to 28 deg. (directed away from
the AR). In addition to the limb-to-limb 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 for the line widths
to be affected by the solar rotation, the spatial gradient of the upflow
velocities must be large enough such that the line broadening exceeds the
thermal line width of Fe XII. Finally, we find that upflows occurring in pairs
or multiple pairs is a common feature of ARs observed by Hinode/EIS, with up to
four pairs present in AR 11575. This is important for constraining the upflow
driving mechanism as it implies that the mechanism is not a local one occurring
over a single polarity. AR upflows originating from reconnection along
quasi-separatrix layers (QSLs) between over-pressure AR loops and neighboring
under-pressure loops is consistent with upflows occurring in pairs, unlike
other proposed mechanisms acting locally in one polarity.