Maps of the line depth ratio of a weak SO₂ multiplet around 1345.1 cm⁻¹ to the CO₂ transition at 1345.22 cm⁻¹. Data correspond to the July 12 and 13, 2017. It can be seen for each day that the SO₂ plumes follow the four-day rotation, corresponding to an angle of 15° westward for a time difference of 4 h. In both cases, the intermediate maps taken between the first and last ones reproduce the SO₂ pattern shown in this figure. The subsolar point is shown as a white dot.