Panels a and b: y − t intensity images from IRIS SJI 1400 Å and Si IV 1393.77 Å. These images are very similar. We compared IRIS SJI 1400 Å TS (black line) with Si IV 1393.77 Å (two times Si IV) from two different locations (panels c and d) to understand the similarities and differences in the nature of both TS. Panel e: histograms of the correlation coefficients for QS (black) and plage (red). The plage histogram is sharply peaked towards high values.