Spatial temperature and velocity maps of the time series. Panel a) temporally averaged temperature ⟨ T ⟩ _t vs. optical depth. Panel b) ⟨ T ⟩ _t minus temporally and spatially averaged temperature stratification ⟨ T ⟩ vs. geometrical height. Panel c) temperature at one scan step minus ⟨ T ⟩ vs. geometrical height. The z-axis in the panels b) and c) is stretched by a factor of five relative to the x-axis. The black lines at the lower border of each panel denote the total circular polarisation along the slit in arbitrary units. The blue lines show one flux tube model of SO91. The orange/red/purple contours in panel b) mark temperature excesses of 50, 100 and 150 K, while in panel c) they denote temperature excesses of 100, 200 and 300 K.