Top: map of the line depth of the weak CO₂ transition at 955.3069 cm⁻¹, corresponding to the observations from March 28, 2015, shown in Figs. 2 and 3. Bottom: map of the PH₃/CO₂ line depth ratio. The subsolar point is shown as a white dot. The negative values on the map of the CO₂ line depth (top) indicate a different behavior of the temperature profile at the level of the polar collar at high southern latitudes.