Sketch of observing geometry between Solar Dynamics Observatory (SDO) and Solar Orbiter for observations used in the study. The coordinate system is with the Earth and the Sun at fixed positions, as seen from above. While SDO observes the Sun from the Earth’s perspective, on the horizontal black line, the Solar Orbiter varies its view angle between the two red lines, moving from right to left (i.e. approaching the Sun-Earth line). The spacecraft illustrations are provided courtesy of ESA and NASA.