A comparison of the longitudinal distribution of equatorial SO₂ column abundances with various other Io longitudinal datasets. All datasets have been normalized to a peak value of 1. (a) A comparison with two datasets showing the distribution of Io’s volcanic hotspots. (b) A comparison with four datasets showing the distribution of SO₂ surface ice. (c) A comparison with a model that takes into account both eclipses and surface frost variability, with the eclipse effect dominating. See the text for details.