On the formation height of low-corona and chromospheric channels of the atmospheric imaging assembly (AIA) onboard the solar dynamics observatory (SDO)

The multiwavelength data from the Solar Dynamics Observatory is extensively used in studying the physics of the Sun and its atmosphere. In this study, we estimate the formation heights of low-corona and chromospheric channels of the Atmospheric Imaging Assembly (AIA) over the atmospheres of sunspot umbrae during the quiet condition period within 20 different active regions. The upward propagating slow magnetoacoustic waves of a 3 minute period, which are perpetually present in sunspots, are utilized for this purpose. Employing a cross-correlation technique, the most frequent time lag between different channel pairs is measured. By combining this information with the local sound speed obtained from the characteristic formation temperatures of individual channels, we estimate the respective formation heights. The median values of formation heights obtained across all active regions in our sample are 356, 368, 858, 1180, and 1470 km, respectively, for the AIA 1600, 1700, 304, 131, and 171 Å channels. The corresponding ranges in the formation heights are 247–453, 260–468, 575–1155, 709–1937, and 909–2585 km, respectively. These values are measured with respect to the Helioseismic Magnetic Imager continuum. We find the formation height of UV channels is quite stable (between 250 and 500 km) and displays only a marginal difference between the AIA 1600 and 1700 Å channels during quiet conditions. On the other hand, the formation height of coronal channels is quite variable.