Evolution of the line profile characteristics of Si IV (1394 Å) along the loop. Panels a and b: total intensity (T_SG) and Doppler shift (v_D) of the single-Gaussian fits to the line core. Panel c: residuals of the intensity in the blue wing (R_blue), the red wing (R_red), and over the whole line (R) as defined in Eqs. (1)–(3). Panel d: red-blue asymmetry (A_r) as defined in Eq. (4). Because we follow a parcel of gas that moves along the loop, the top axis shows the time to indicate the temporal evolution. See Sect. 3.5.