Study of 4.22–4.295 μm spectra averaged over latitude bins. A) Pearson correlation coefficient between residual CO₂ DIFF spectra and a synthetic DIFF spectrum which uses a CO₂ fluorescence synthetic spectrum at T = 105 K as input. B) CO₂ line-of-sight column density retrieved from the fit of CO₂ DIFF spectra. C) shift, in fraction of spectel, of the maximum of the cross-correlation function (CCF) between CO₂ DIFF spectra and the synthetic DIFF spectrum; secure detection is indicated when the shift is close to zero. D) S/N of the cross-correlation function at shift = 0. The S/N is obtained by computing the CCF_noise obtained by using as input a simulated noisy spectrum, with the r.m.s deduced from the ERR entry in the Level 3 data cube, and scaled in $\sqrt{n}$, where n is the number of averaged spaxels (S/N = CCF/CCF_noise at shift = 0). In all plots, blue and red symbols correspond to the leading and trailing sides, respectively. The blue (resp. pink) vertical domains show the latitude range of the open-closed field-line boundaries for the leading and trailing sides, respectively, restricted to longitudes of 10–130° W (leading) and 210–330° W (trailing).