Amplitude of the Gaussian fit for the strongest chromospheric emission lines. In case of multiple line components, the strongest narrow fitting component is shown (Hα, Hβ, Ca ii K). The time interval covers the first 2.3 h of observations, including the flare onset at 2:58 UT. For fitting Hα, a PHOENIX spectrum has been subtracted; the change of the green hue indicates that the fit switched to another line component (see text). Colours are indicated in the legend; both Na i D lines are denoted in red.