Model field at 00:04 UT just before the arcade eruption and the flare, derived from the PFSS package of Solarsoft, whose perspective has been rotated to 04:50 UT in order to compare with the extended blueshift region observed by EIS in Figure 3(d). It shows a narrow open-field corridor between two closed-field domains. The open-field corridor extends northward to a coronal hole. The blue dashed box shows the same region as the bottom left corner enclosed by the dashed line in Figure 3.