Top: time-distance map following the expansion of the bright elongated feature in the SUVI images (the time coordinate starts from 21:17 UT on August 21). The blob presents as the tip of the expanding feature, which can be tracked by the dashed gold line. Bottom: variation in the height of the blob seen in SUVI images (diamonds with a dashed line), which was identified manually. The solid line is a second-order polynomial fit to the variation curve.