  One of the major discoveries of Hinode's Extreme-ultraviolet Imaging
Spectrometer (EIS) is the presence of upflows at the edges of active regions.
As active regions are magnetically connected to the large-scale field of the
corona, these upflows are a likely contributor to the global mass cycle in the
corona. Here we examine the driving mechanism(s) of the very strong upflows
with velocities in excess of 70 km/s, known as blue-wing asymmetries, observed
during the eruption of a flux rope in AR 10977 (eruptive flare
SOL2007-12-07T04:50). We use Hinode/EIS spectroscopic observations combined
with magnetic-field modeling to investigate the possible link between the
magnetic topology of the active region and the strong upflows. A Potential
Field Source Surface (PFSS) extrapolation of the large-scale field shows a
quadrupolar configuration with a separator lying above the flux rope. Field
lines formed by induced reconnection along the separator before and during the
flux-rope eruption are spatially linked to the strongest blue-wing asymmetries
in the upflow regions. The flows are driven by the pressure gradient created
when the dense and hot arcade loops of the active region reconnect with the
extended and tenuous loops overlying it. In view of the fact that separator
reconnection is a specific form of the more general quasi-separatrix (QSL)
reconnection, we conclude that the mechanism driving the strongest upflows is,
in fact, the same as the one driving the persistent upflows of approx. 10 - 20
km/s observed in all active regions.
