From left to right: IRIS Mg II h core full-disk mosaic, AIA 171 Å and 193 Å images from April 13, 2019 (top panels) and May 5, 2019 (bottom panels), when the ARs NOAA 12738 and 12740, respectively, were on the disk. These two examples show the appearance of the DHs at the disk center and the solar limb, respectively. DHs are dark areas best seen in TR or low corona lines, such as Fe IX in the AIA 171 Å waveband. In the chromosphere, such as in Mg II h&k line cores, fibrils are often observed right next to the AR cores.