Comparison of the observed (crosses) and modelled (coloured lines) brightness of four emission features, OI1356 (a), CI1657 and CO4PG (b), Lyman-β and OI1027 (c) and OI1304 (d), during four time periods, during which a CIR was observed at comet 67P, on 4 Aug. 2016 (see Table 4). The observed brightnesses are from three regions of the FUV spectrograph slit (rows 8–11 [red], 13–16 [black] and 18–21 [blue]). Vertical black lines link simultaneous measurements of the brightness.