Top: 171 Å image at August 29, 2017 08:49:45 of the SDO/AIA ROI just before the beginning of the SST dataset. The green and black contour represent, respectively, the regions detected with normalised power above 5σ (extended contour) and 10σ. The white arrow indicates the north direction. Middle: normalised power map at 42.2 μHz (i.e. 6.6 h) for the 171 time series. Bottom: normalised power map at 46.1 μHz (i.e. 6.0 h) for the 171 time series. The scale is saturated to 15σ for both frequency bands.