Chromospheric temperature profiles. a) Different theoretical temperature profiles for the chromosphere above a sunspot: solid line from Maltby et al. (1986), dashed line from Lites & Skumanich (1982), and dotted line from Staude (1981). b) Flat and step chromospheric temperature profiles with the photosphere at 0 and the transition region at 1.8 Mm. This chromospheric profile is shown in relation to the photospheric and coronal temperature profiles in Fig. 1. The step profile is a simplification of the theoretical temperature models shown in Fig. 2a.