Observing the lower solar atmosphere. The x- and y-axis represent the position in pixels. One pixel corresponds to 0.3 Mm. The resolution of the z-axis is one-tenth of the resolution of x- and y-axis. (a) Left is the visualisation of the lower solar atmosphere embracing NOAA AR 11745 (upper left sunspot group) and NOAA AR 11744 (sunspot group in the middle right). The bottom panel is the photospheric magnetogram, the top panels are taken by the sodium MOF with two peaks (600–700 km) and a single peak (800–850 km) at UT20130513T030854. Because the vertical scale is much larger than the horizontal one, the bottom panel is hardly visible. (b) Right is the view from the top.