Evolution of CH₄ and NH₃ during the first ~2.3 days (P_Wind/2) after the start of the flare event in the upper atmosphere (1 μbar) of the evening limb. Three simulations are shown that correspond to 2 × 10³³ erg flares of 2 (dashed-dotted), 4 (dashed) and 8 (dotted) hours. The simulation discussed in Sects. 4.1 and 4.2, with a flare of t_col without exponential decay, is shown by the solid line.