Reproduction of Figure 3 in M. C. Wong & W. H. Smyth (2000), showing modeled vertical TPs at the subsolar point for high-density (T_ss = 120 K) and low-density (T_ss = 113 K) atmospheres. Here T_ss denotes the subsolar surface temperature, which sets the boundary condition for SO₂ sublimation. Panel (a) corresponds to western elongation (Io’s sunlit trailing hemisphere), where plasma heating on the dayside leads to a more extended atmosphere. Panel (b) shows eastern elongation (Io’s sunlit leading hemisphere), where reduced dayside plasma heating results in a cooler, more compact atmosphere.